GME TX3520 cuts out

Hi all, I have  GME TX3520 UHF fitted to my 4x4 lately I have noticed it wont turn on every time. It seems to work randomly and might go for a day with constant starting of the car but then it suddenly cuts out and wont start for a period of time. Once or twice it has actually been on and cut out suddenly and without any interference or adjustments of anything close to it. Any ideas on where to look? Cheers and TIA ;)

Question by AllanW28   |  last reply



Uhf and Vhf Radio Waves

Hi i have a problem i need  device for sending(transmitting and receiving) radio waves with data(binary code or hex code) and receive it. what material i need?and how to send data with this board.could i use raspberry pi? i need to boost this signal for 100 km and more .

Question by HosseinJ4   |  last reply



Auto switching 3.5mm circuit

I currently have my phone connected to my car stereo via 3.5mm audio cable on the aux input for music playback I would also like to connect my UHF radio to the car stereo as the internal speaker is not very loud/clear. I would like it set up so that the music is playing and it auto switches to the UHF when someone is broadcasting. I'm not sure if such a thing is possible (DIY) or if a product existing on the market already. I would appreciate any help on the subject Cheers 

Topic by aparks   |  last reply


RCA converter project

I have an old TV that I want to convert so that it's able to be used as a monitor for my camcorder. The TV however only has an antennae and screws on the back for a circular UHF antenna. It's an old RCA Model EJR 291S black and white tv. If anyone has any ideas let me know.

Topic by mrshow555   |  last reply


Coaxial cable to UHF coat hanger antenna?

Greetings, I need to make a UHF TV antenna.  The TV has a coaxial plug on the back, and I have coaxial cable, but I do not have an adapter. What is inside the adapters that go from coaxial cable to two wires?  Any electronics?  Do the two antenna leads just connect to the pin in the center? Thanks

Topic by NeuroPulse   |  last reply


What radio frequencies will be legal for wireless microphone use in 2012? Answered

Hello, I will be wanting to purchase UHF microphones that comply with the new frequency changes in the UK. I have found many recourses on the internet but none seem to match up? I would be very grateful if someone were to tell me what channels you can operate on (license exept) in 2012. Many Thanks Oscar

Question by oscarthompson   |  last reply


Is there a durable, waterproof UHF HT that will accept AA batteries?

By waterproof, I of course mean "weather-resistant." I'm looking for an UHF HT that will be just fine if it gets dropped into a lake or falls off an ATV. It doesn't need to float; I can attach a floating keychain to it if necessary. It should also have a AA battery tray that is available from the manufacturer, and still be waterproof with the AA tray. Ideally it would have a keypad. Do you have personal experience with a HT that meets these requirements?

Question by JamesRPatrick   |  last reply


Can multiple UHF receivers share antenna's? Answered

I have multiple UHF microphone units. They have two antenna's on the back of them, it picks whatever is the strongest signal for 'true diversity'. My question is, Instead of buying those really expensive antenna distribution units. Would I be able to group each of the antenna connections from the units to one antenna for each side and use two high gain UHF antenna's to receive the signal. I would think that the receiver units would pick out the signal individually as they are set on different channels. All the units are exactly the same with the same antenna's. I could be very wrong with this however! Any feedback is very welcome! Thanks

Question by oscarthompson   |  last reply


TV antenna

Is it possible to make a tv antenna from an old router? I have an old router and a tv antenna. I am trying to do this because my stupid cable provider won't pick up a second CBS. Then my TV tower fell about 5 years ago. Last month I found this station. It's 79.2 miles away. My little indoor TV antenna pick it up at NIGHT, on CLEAR skies only. (Not in the day) and I have to hold the antenna. I know routers would be didgital (if that has anything to do with it). My tv does have the digital tuner. On digital I can't pick it up, but i do somewhat on analog.

Topic by popit   |  last reply


Long Range UHF RFID Integrated Reader

Hi, I am Planning to develop Long Range UHF RFID Integrated Reader which can Read Multiple Tags at a time (range between 8- 15 Meters range) and send information to my web application to store data, so will you plese let me know the components which i need to use along with assembling process. Thankq

Topic by bikhanpersonal   |  last reply


UHF CB radio antennas or scanner antennas anyone?

For a while now I am back to experimenting with various antenna designs for my UHF radio.Started as something entirely different but who cares LOLAnyways, we usually have either a standard whip antenna or a vertical dipole design for mobile use, like on your car.This is a very good design for both types of antennas, mostly due to the short wavelenght compared to the "old" 2m or 27mHz CB radios.Fun fact for at least AU in this regard is that back in the day everyone jumped onto UHF to get away from the overfilled chatter on 27MHz, now the old 2m band is basically dead except for marine use.One thing I really miss on UHF though is distance!Line of sight communication sounds fine at first but then you really have to realise the limits once out and about.As a result we often have to choose between a high gain antenna or a stubby for going into the mountains or being in a convoy.Only way out seems to be the golden middle by opting for one of the 4.5 - 6-5DBI antennas.Neither solution really satisfies me though :(To get around the limitations and have some fun again when sitting high on a mountain I compared various commercial antennas I had.You know, pick someone with a weak signal coming in and hope he hears you and has some time for a chat.Turned out there is not really that much difference in terms of receiving a signal.Quite huge differences though when it comes to the other side being able to hear you!So I jumped onto a basic SWR meter and actually checked my so called factory tuned antennas - all but one were way off the charts here.At least if you are like me and like optimised instead of compromised antenna systems.A Standing Wave Reflection ratio of 1:2 or even 1:2.5 is seen as very acceptable thing on UHF for some weird reason.Back in my glory days no one I knew would have accepted anything above 1:1.3 for his 27MHz system, be it mobil or a station at home.Sure enough, repeating my long distance tests a few days later with tuned antennas resulted in far better results.An antenna for long distance calls or emergencies?!The easiest way to get more distance on UHF is obviously getting the antenna as high as possible.From a nice mountain top you have it way easier than in any urban areas for example.Explains why so many of the long and sturdy antennas are just simple dipoles on a long pole.If you ever checked the feedback for these double quad TV antennas you realise they are literally in the same frequency range.Similar story for all the Yagi antennas for our TV sets that you find on so many roofs these days.Only problem with them is that they usually don't give a damn about transmitting qualities.And of course that they are usually providing around 300Ohm instead of the 50Ohm our radio expects.A TV needs 75Ohm and a balun is used to provide a isolation as well as a matching for the TV.Needless to say I could not accept this ;)My first design was made from aluminium foil glued onto some printed and stiched pages for a double quad.1MHz bandwidth is quite narrow, so the basic square design with about 13.8cm for the sides of the squares was easy.To my surprise by just adding standard RG58 cable this design was very close to 50Ohm already, I had around 60.A few glue sessions later I was able to match it to 52Ohm - close enough for test.Did not want to risk anything with my expensive Icom so I used my cheap Baofeng handheld for the initial tests.Indoor mind you...To me disappointment I seemed to be unable to pick up anything.So let the sanner run and waited...After being bored enough I decided to pick, starting with the antenna and when I moved it the handheld suddenly had a clear signal.Desperate as I was I grabbed the radio and waited for the chat to continue - nothing again...Then it finally hit me: The double quad is quite directional....Sure enough by just turning it slowly I was able to pick up chatter on various channels.Once brave enough to risk it I even got confirmation that people about 10km away could hear me just fine.Time to scale it up a notch...Next design already had the directional problem included as a design feature.I added a director in the front and a reflector in the back.The endless hours of glueing and cutting were replaced by using 12mm wide copper tape and sturdier cardboard.A test with my car on a little "mountain" and the antenna on 2m pole mounted to roof rack gave me, for the first time ever, conversations with people that were over 30km away.I am currently trying to make the entire thing omnidirectional.The omni quad....If you take two double quad antennas and mount them at a 90° angle you end up with very nice 2-lobe pattern, 4 lobes if you don't use a reflector.Problem here though is that these designs really mess with your antenna matching.Not to mention that using it while driving only works at quite low speeds.One day I will do the final design in stainless steel wire though...Anyways, using the directional properties to get an omnidirection radiation pattern meant using 4 seperate antennas with a reflector for each of them.Still left a few dark spots at short range but otherwise really nice for long distance if you don't want to constantly turn your antenna.Getting 4 antennas down to 50Ohm on the connection to the cable was painful to say the least.The problem of taking care of distances to be in the sweet spot for the 477MHz range also meant the design ended up to be quite bulky.One of my lightbulb moments providing good ideas caused me to use one reflector with a double quad either side.Worked almost fine but again provided totally different values to somehow match if it ever should transmit a signal without damaging the transmitter.Obvious conclusion was to buy a new roll of copper tape and to try to get four single antennas into one "housing" without stacking them.Bad idea here was to cross the antennas :(Better idea was to make 4 pyramids out of carboard and aluminium foil.Sadly this resulted in a failure because the 4 sides of the pyramid reflect the signal not flat bt at their corresponding angles.Had to make it really big and use 90° angles, resulting in the signal being reflected like light in these cat-eye reflectors on your bike.After wasting a few days to create the real thing it turned out to not really work properly for the reception already.Even close range signals came in really distorted.I guess the double reflection meant the phase is shifting and cancelling out what the antenna gets.My last desing idea for testing will be with a different approach.Instead of 1/4 Lambda elements I will use small 1/64 Lambda elements.Only about 2cm long means that matching is pain in the behind but if the purpose is just receiving it should be fine.The reflector will be four flat sides like a box with antennas in front of the sides and the cables joined in the center.If you like to fiddle with antennas and don't mind trying a weird looking base antenna on your roof I might be willing to write up a short Instructable based on my designs - let me know in the comments....By the way: it is quite easy to desing this for the common 2.4GHz Wifi bands ;)

Topic by Downunder35m   |  last reply


crc9 and uhf does it 3g and couple other questions?

First whats stronger rg-58 or rg-174 when going long length say 5 meters for 3g crc9 3g dongles? (mainly huawei dongle e160e) crc9 to uhf antenna work for 3g dongles? crc9 socket has two soldered tabs on back what is that about, is it when the crc9 is plugged in the middle crc9 male pin crosses these somehow?  oh and 1 more question what is the crc9 socket on the huawei pcb called? cant find replacement socket due to no-knowledge

Question by bubbadamage 


CB radio antenna question(s)....

I have a UHF CB radio in the car that is now quite outdated.Waiting for a 80CH replacement to arrive so the old one can be used as a fixed station in the house.Recently I made a new straight whip for the car as the fibreglass one snapped off.Now the problem I am facing is a total between reality and computer simulation.Here is what I did:Started with a straight steel wire on the elevated mounting - this spring mount is supposed to provide a ground plane as it was originally for a ground independent antenna.Simple math tells that a 1/2 Lambda whip should be around 33cm long, so I started with 40 and used my truted SWR meter.As it turned out my antenna was too short !?Tried again with a longer wire and got a good SWR reading of 1.09 with a total whip lenght of 49cm.As the elevated mount basically turns the entire antenna assembly into a vertical dipol I decided to simulate the thing in Mmangal.Should be straight forward, diameter and length of the ground rod, wire length and diameter for the actual whip.But with the same dimensions I have working fine on the car Mmangal tell me my antenna is totally out of whack.Calculated SWR is well over the 15 and the antenna is not anywhere near resonant in the 470MHz band.Mmangal is mainly for lower frequencies but shouldn't it work for the 70cm band as well?If I design the antenna as a classic ground plane with 3 or 4 radiating elements sloped at 42° I still get nowhere with my whip length.Since my SWR meter is correct and the antenna working really well I am wondering where my problem with Mmangal might be?Anyone here using it for 470MHz or with some insight on how to get the correct values for a vertical dipol antenna with a rod for ground and wire for the whip?

Question by Downunder35m 


"Secrets" about CB/UHF antennas on your car

Despite more and cellphone and internet coverage mobile radios are still a favourite of people in remote areas or just loving to explore by 4WD.And for most the complex task of starting with this great hobby ends by buying a radio and antenna.Of course the raio goes it fits best and that is fine but what about that antenna and while at it what type of antenna do you need?Let's start with the great myth that so called rugged or heavy duty antennas are really worth their money.Durability and stiffness is their main selling point or better was.At highway speeds they won't bend and flex around like your whip antenna.In the bush they won't swing all the way down onto the painted parts of your car either.But then again, a more solid steel whip on a spring base would do the same - but won't look as cool or proffessional...Inside those plastic or fibreglass rods is a dipole antenna, in rare case you get a 5/8 configuration or even a normal steel whip with a pipe around it...Means in terms of reception or transmission quality they are not a tiny better or worse than any other antenna out there.Come down to well it is tuned and where the radiating part is located.Location...There are often obvious choices to put an antenna, like that nice mount or your nudge- or bull-bar.Or the good old boot clamp in the back.I have even see 4WD's with the antenna mounted onto the rear bumper :(Why is it so important to place the antenna correctly?Place on the front corner of your car it is not only quite low but also partially covered by the metal parts of your car - limiting where the antenna can properly radiate.If you ever got some half decent training on a tiny handheld UHF radio then you remember to seek higher ground if you can't get anyone to hear you.The same is true for the antenna on your car.You want nothing obstructing it.People with a long spring base often think of it as just an elevated foot.Most of these however are "ground idependent", which means they actually form a dipole with the antenna you screw on the top.Having this "pole" below bonnet hight is quite bad for your reach and reception quality already.Mounting just a normal whip on a direct foot here means you might have better luck with a handhelp from inside the car...The best would be right in the center of your roof, the highest and most centered point.This provides not only the optimum radiation pattern but also give you that little edge in terms of higher ground.How much gain do I need and how long should my antenna be?Gain is quite relative if you ask me as it far more important to mount the antenna in the best possible place.A 3DB antenna on the roof will often provide better reception and range than a 9DB mounted on the bullbar.Assuming you have the best feasable location than to simplify it:The further you can see the higher DB you want if reaching far is the main objective.For general use a 4.5 - 6DB antenna is always good.In hilly terrain range does not matter that much, here you want the outgoing signal to be as strong as possible and with a shape that allows better coverage by being more like a sphere.For extreme cases it can mean on a 9DB antenna your friend that is just over that little bump ahead is not visible and with that can't hear you.On a 3DB antenna however the signal is strong enough to reach that blindspot at a short distance.The overall length of an antenna can be deceiving for UHF frequencies.What matters is where the antenna is radiating from.In most cases it will be the top 15 to 30 cm of your antenna.For a dipole or ground independent antenna you often need to include the entrire base mount.Antenna tuning....For the good old 27MHz bands we always had our SWR meter at hand and tried to get the best tuning.Since the big jump to UHF the commercial antennas come pre-tuned and are claimed to be good to go.That means that are within acceptable performance to fit almost all installation locations.In terms of SWR reading it means that 1 over 3 is still perfectly fine.Would have been an outcry on 27Mhz though in my times.What is true though that there is not that much real difference to notice between a near perfect 1 over 1.1 to 1 over 3.If you would bother to a distance test it might be less than 200m you gain on the near perfect antenna.For the reception it does not even matter all, so why bother anyway?On the much lower frequencies a really good SWR does not only mean you can get your signal much further out there but also that your transmitter is happy.Modern ones are now all digital and have ways to protect and compensate for bad antennas or cables.Together it means we could just forget about these few extra meters and move on.The stress on the transmitter in your UHF radio however is still there ;)The reflective energy from a badly tuned antenna has to go somewhere and that is usually back into the transmitter.The bit that lost directly to your antenna, as said, does not matter too much with the overall limited range of the UHF frequencies.I did quite a lot of experimenting with my own and commercail UHF antennas, so a network analyser and SWR meter was a requirement anyway.In terms of output power a good SWR reading means you get what your transmitter is capable of and set for.With an SRW reading between 2.5 and 3 however a 4W radio might only actually transmit 3-3.5W.With a bad mounting and an not so optimal cable it might go below 3W!Distance is not so much affected by this as we now know, but the loss in power on 3DB antenna in hilly terrain can make the difference between being heard and your signal getting lost in static on the other end.Repairing a blown transmitter often costs more than a simple SWR meter for UHF, so why not add it to the Xmas wish list? ;)Two antennas...In some case you want two antennas.Be it for two different DB ratings on the same radio or for totally different frequencies.High and centered is still best here but you should keep the antennas as far apart as possible, preferable at different heights as well.On a single radio it does not matter too much but right next to each other the unused anteanna is like these beams on your TV antenna on the roof.Unlike the directional and watned features in a Yagi antenna the unused element means we change the radiation pattern.In the worst case creating a blindspot from which direction we won't get any signals.As a rule of thumb let them be apart at least twisc as far as the wavelenght, so for UHF over 65cm.

Topic by Downunder35m 


homemade signal booster? Answered

I was trying to figure out how to boast my signal coverage in my area, and a got an idea: to use a UHF amplifier, to pick up the towers signal and rebroadcast it. of coarse since things like WiFi, Bluetooth, and cellular 2G/3G/4G networks use two way radio, the signal can go back to the reviving end of the UHF amp, and get broadcasting to hit whatever tower. my phone should better recognize the tower, as if i just magically made a tower 2 feet away. however this might also amplify stay noise. if this idea doesn't work, why not? i think i am going to need at least a 20dB increase in power, but as of now i  need to do more research. but if i can buy a product that does a similar thing for less than $40, i would. http://en.wikipedia.org/wiki/Dead_zone_(cell_phone)#Dead_zones  http://en.wikipedia.org/wiki/Repeater http://en.wikipedia.org/wiki/Wireless_spectrum (cellphones use UHF spectrum) http://en.wikipedia.org/wiki/Signal_booster

Question by -max-   |  last reply


Motorcycle communication without expensive BT headsets!

When it comes to communicating with the person on your back seat then often there is no need for a fancy BT headset.Unless of course you are constaly driving on freeways at high speed and love to talk ;)The most annoying thing though is when you want to go for a long ride with a lot of your mates.Some might already have some BT headset, most might not have anything to communicate.Even with just 8 or 10 riders in your group, loosing one is easy.The most advanced headsets now offer functions for automatic pairing when the connection was lost - they come at a price though.Around here there is two problems to face when going for long rides.a) communication range for the riders in the group.b) cellphone coverage is usually non existing when you actually need it.So why not go with something totally different and much cheaper than BT headsets?At highway speeds the range of BT headsets suffers not just from the required safety distance between riders but also from the spped itself.Cheap headsets just crap out all the time, expensive one tend to loose the connections quite often.Wouldn't it be great to have more than the average 800 meters of good sound quality without dropouts?And if you ever tried to have a decent converstation with another at high speeds you already know that even the best BT headsets struggle with the wind noise unless you have a really optimised helmet (and paid a lot for it).The alternative, if we trust all the hype and advertsiements would be to go for the latest generation of headsets out there....Baofeng UV-5 series....This type of UHF/VHF handheld radio has ben around for years.It is not only quite cheap but also able to put a full 4W out.So called battery eliminators to power them directly from a 12V socket (in your car) are cheap as well, but a good battery should last for a few hours.The benefit of these cheap radios however is not that they are so cheap.It is that you can actually program whatever frequency you like for your needs.Of course you should stick to the frequencies and channels that are free and legal to use in your area.The since is about what a pack of smokes is, so no problem to mount it descreetly on your dash or handlebars either.Being a radio there is no need for pairing or making sure you stick to the correct order when doing things.If you want to be "alone" on a channel you can even use celectcall and other option to make sure only those radios with the right callsigns wil open your squelch.Quite nice if you suddenly get into an area where your channel is used by ther people.Ok, a handheld radio might work, but what about the antenna?The UV5 series usually ships with two antennas.A short stubby that is good for about 1-2km - line of sight.And a small external antenna with a magnetic base.On a bigger bike it is often no problem to add a 15x15cm plate behind the seat that the antenna can pop on to.Should only be required if your require a bigger distance though.And why would a UHF radio be any better with the background or wind noise?Biggest problem with these expensive BT headsets is that you need to get really creative if you want to change the speakers or microphone.And options are quite limited here again - either a flexible microphone or a glue on one.Neither is really good once the wind gets too much.For the UV5 series you get so called throat microphones for under 10 bucks.Often advertised as tacticle headsets but for the price nowhere near the quality of a military grade combination.They plug straight into the handheld and come with an external push button that can be used to start a manual transmission.But of course you can automate this on the UV5 as well by selecting the voice activation mode in the menu.Set the level so high that you need a slightly rised voice to start the transmission.(That way not everyone needs to hear you swearing about other drivers if you keep it quite ;) )All up a solution like this will cost you well under $100, with all required extras.For a bit more you can also get UHF radios for helmet use.Basically the same like the handheld option, but smaller, a bit more convient to use and set up but also very limited in range and battery life.

Topic by Downunder35m   |  last reply


Can I substitute a vertical antenna for a dipole? (Also, how do I protect it from lightning?)

I have a project that requires a 87 foot long dipole antenna. Would it be possible to use a 44 foot long quarter-wave vertical antenna in place of it, to save space? And is there any DIY way to protect the antenna from lightning? How well do they work compared to store-bought lightning arrests?

Question by ElectricUmbrella   |  last reply


Challenge - RFID reader + Wifi Module Low Cost.

Hi Guys,I'm an Oracle Architect and I have one customer that want to monitor water dispenser, he wants to know if water bottle was changed. I have a software to control it, but actually the people need to input this data manually and I would like one solution to do it automatically. I'm thinking to use RFID Reader on water dispenser and paste passive tag on water bottle and with this I'll receive the information and this data must to be send using wifi, I can't have cable in this solution (data and power cable is not possible). In my investigation, I just find rfid reader (UHF) able read a passive tag in 1 meters distance, the issue is, the UHF module is very expensive, I saw UHF module for 40 USD and I need something more cheaper. Is there another way to do it? I need suggestions and help to developer it.If need more info, send me email.Regards, Haysar Lelis

Topic by HaysarL   |  last reply



Heavy duty UHF CB radio antennas and why cheap can be much better....

If you not a fan of normal road cars then you might get some 4WD and go off road every now and then.There are even those doing trips to remote locations that take a few weeks.An essential piece of equippment these days is a UHF radio.In a convoy you might get away with a handheld one if the cars are not too far apart and the terrain suitable.Most peole however opt for a permanent installation in the dash or roof console.After that decision comes the hardest and often costly part: What antenna to use....If you trust certain online reviews and manufacturer claims then one thing becomes quickly obvious.If you need a sturdy and powerful antenna then you have to pay top dollar.Some come with heavy spring bases claiming to protect the heavy fibreglass rod if you hit a bush or trees branch.There is always a compromise between weight and stability.And trust me, on the right corrugations you prefer not to look at your antenna....So how are these expensive antennas made?As I don't have any own pictures and don't want to steal them from the net: Please search for the terms used if you don't know them already.To answer this let me go to the other types of antennas you can get for your UHF radio.There is the famous rubber ducky - a stubby antenna best suited for short range on difficult terrian.Then we have the fibreglass whip antennas that have more or less coils integrated or even consist of one single coil with different spacings in sections.Good for normal road use, not so much off road as they won't tolerate too much vibration, they often snap off the base screw.Most people now just ignore the short whip antennas of 15 to 30cm length as they usually only come with a gain of around 4.5-6db.I will explain later why that might be a misconception.The last ones are those steel whips with one or two "loading" coils.These coils electrically shorten the antenna.They also provide a matching to the 50 Ohm required for most transmitters and antenna cables.Usually they are designed to be 5/8 Lambda antennas.A good antenna for just receiving, like when using a scanner is not critical in length.Transmitting however means you need a proper Standing Wave Reflection or SWR ratio.For this the antenna needs to be tuned.To be of any good use your antenna needs to match the transmitting frequency.This works best if the antenna length is at 1/2, 1/4 or 5/8 of the corresponging frequencies wavelength.Also called Lambda if you look for antennas.In the good old 27-MHz days we were used to quite long antennas in our backyard, for the car we then opted for 1/4 of this - usually around 2m in length.For UHF however 1/4 wavelength already means you are down to about 16cm...Going for 1/2 is a good thing here as it is still quite short at about 34cm.Real difference when it comes to these Lambda factors is the radion angle produced.You can imagine a 1/4 to look like a huge donut with no hole, about 25° for the radiation angle.At 1/2 this will be flattened out to around 20°.A 5/8 Lambda ntenna can get as low as 16°.Imagine it like a flashligh that has adjustable focus.The light source is of fixed output as your transmitter.The lens does the job of the antenna.If you make the beam more narrow then the light intensity of a certain areas at a certain distance will increase.Means for the radio you get a longer distance your signal can travel with enough energy.This however comes at a price!Imagine you are at the bottom of quite stepp mountain and your mate is up on the top about 2km above you.A high gain antenna with a narrow radion pattern might not even reach up there, while a short stubbie with just 3db still has a chance due to the more spherical radiation.Also explain why low gain and with that short antennas work best in hilly terrain...Back to the thick ones...As you can see you can basically hide any type of whip antenna into a fibreglass rod.But most of the are as said "ground independent", means unlike your normal whip they don't need the spring or foot to be of low resistance to your car's body.How does that work?Well, exactly like these ground independent whip antennas with a spring base or metal pole base work.You know the earliest antenna was a dipol - look it up on Wiki ;)For our CB radios that means you have a metal rod or spring that is about 1/4 or in some cases 1/4 of the wavelenght long.This is connected to the shielding of the coax cable and provides the required ground for the mounted antenna.The big difference is that only too often a dirt cheap dipol is hiding in your expensive fibreglass rod ;)The complete antenna might bring over 2kg on a scale, but the actual thing allowing you to receive and transmit is a few grams of coax cable...HOLD ON A MINUTE!! Some will say now...My whip is 70cm long and my expensive heavy duty one with 9db is 2m long - how does that work with your wavelength theory??Well, it is not my theory, just a fact ;)Imagine a 1/4 Lambda dipol, then it would be all up around 35cm long.And funny enough, that is about the length of a $180 heavy duty stubby if you just tak the rod itself.Go 1/2 of Lambda and you get an overall length of the dipol of around 65cm - add the metal rod making the crew that holds the fibreglass rod and you have the common 70-75cm heavy duty antenna...Anything above this length usually is either just a long rod with noting above the 75cm mark or simple has the 75cm long dipol made from the coax cable at the top with the antenna cable going down the otherwise empty rod.Ok, I got it, either 1/2 of the wavelength or 1/4, so about 35 or 16cm long.Ground independent we add either 1/4 for the spring base and rod or 1/2 for the longer ones.And how again does it work with the gain of an antenna?If you trust Wiki then it comes down to the radiation pattern.These heavy duty antennas usually come with around 6 or 9db, the short ones with 3-4.5db.These values might give you an indication about the theoretically possible distance you can transmit but nothing about the terrain it is suited for.Common rules of thumb created by those selling antennas and radios is that you a high gain antenna on flat terrain and a low gain antenna in a hilly area.Around 4.5-6db seems to be the golden ratio here as these anteannas are equally bad for both extremes in terms of terrain options.What you really would need to know is the actual radiation patterns in a three dimensional plane.A straight whip or dipol as a more or less donut shapead radiation pattern.However, location affects this!Mounted in the middle of the roof it is closest to perfect, while at the corner of your bumper bar you will distord the donut and also block parts out with the body of your car.This is why for this type of mounting elevated antennas are prefered.Makes no sense to have a 16cm long stubbie mounted so the top is still lower than your bonnet...Any antenna with a loading coil (or several) or top load will have a distinctively different pattern.We speak of so called "lobes".If you see it in 2D then for example a 1/2 lambda straight whip will look a bit like the infinity symbol.A 1/4 Lambda of the same style looks more like two ping pong bats joined without the handles.Those with loading coils or linear arrays made from coax cable however can produce multiple, prefered lobes.Usually they are in the 4-6db range and claim to be "universal" or as "allrounder".Here you get a quite narrow main lobe of 12-16° with one or more but much shorter lobes going upwards at about 10-30° depending on the configuration.At short range, like in hilly terrain both lobes overlap while you get a dead area at greater distances.You can sometimes notice that when you are on a low level talking to someone up high.There are cases when with a bit more difference in angle to each other (in terms of height and distance) the signal jumps up a few numbers.You just went from the dead zone into the lobe ;)With just a db value for the anteanna but no details about the actual design, heavy duty antennas can fool you badly.In mayn cases a 1/2 Lambda straight whip on the roof will outperform a costly, heavy duty antenna mounted to your bullbar.This is the reason why the expensive ones are the biggest cheat - they just elevate a quite small antenna above your roof line.And since it is heavy it needs a big spring and you hope it will not break if you hit something on a narrow track.All while the thin stainless stell whip with the cheap magnetic base just flexes under all obstacles with no damage at all.Plus, if you really get into the thick jungle you can just take the magnet off until you are through LOLWhy is a SWR and power meter still an important tool to invest into?Those remembering or still using 27-MHz radios only know too well why you need a proper SWR and power meter.With the lenght of the antenna at these low frequencies and affecting factors new the antenna proper tuning is a must.The bandwidth of the channels also means you have to tune the lowest and highest channel so the are basically even, anything else and the old guys would scream "UNACCEPTABLE!" ;)Especially it you want to get the last out of your system without going illegal.For some reason we accepted the claims that an SWR reading of around 1:2 is fine and acceptable.Most of the radios lower the power output to protect the transmitter if the SWR goes to far out.Allows for simple mass production of antennas with fixed cable lengths that are usually well overpriced.The most expensive bit is the cable itself here...I had no time to build an analog SWR and pwoer meter that works properly on 27 and 470MHz, so I ordered cheap SW30 from China.With that I first checked my little collection of antennas then those of some of my friends.This includes everything from short rubber duckies over loaded and straight whips to heavy duty models.One thing that was obvious right away: most are far away from an SWR readin anyone with a 27MHz groundplane antenna on a long mast would accept.And only one heavy duty antenna had a SWR readin of below 1:1.6 for channel 1 AND channel 40!That one was relatively cheap noname brand.With that sorted I decided to tune at least my steel whip antennas.To my utter disappointment they were all just a tiny bit too short - a thing that would have caused a proper 27MHz antenna manufacturer to to keep a large stockpile of his antennas...I had one though that was longer than needed.And before you ask: Yes, I tested them on both my elevated bullbar mount AND a direct mount on the roof rack.Did not change much for the bad ones so I ignored the mounting position for the tuning.I checked the power once for both channels on my prefered antenna and got 4.4W.Mind you that one has a SWR reading of 1:2.2 and will no longer be used as I can't be bothered to make it longer.For some reason I thought I check the SWR and power everytime I cut a bit off the antenna instead of just watching the SWR reading.At original length I had a SWR of 1:1.9 on ch40 and 1:1.75 on ch1 with 4.6W.I kept trimming down by about 2mm increments until I got an even readin of 1:1.07 on both channels.And with every trim the power went up a little bit.I have a friend that is or better, was just at the brink of being unable to reach from my driveway when he is parked in front of his house.A radio check after the tuning revealed that instead of coming with a lot of static noise and sometimes cut out I got a solid reading of 2 on his end with a much more acceptable level of noise.However, I still struggles as badly to hear him...Funny thing is that test was with just a plain and straight whip of 1/2 Lambda, in my case the tuning resulted in a length of 38cm from the base of antenna screw to the tip.My fancy 9db high gain antenna that is just over 70cm long did not even reach him while I could hear him slightly better than on my tuned one.Changing the mounting to the roof rack gave me a clear reception and a signal strength of 4 at my friends end with no noise.Elevation and nothing around the antenna does matter...After all this, would I still bother to buy a ready to go antenna for 470MHz?Only if I had to.Getting some RG58 cable or re-using it from on old antenna is cheap enough.A standard screw mount with a grub screw to hold a steel whip sets you back less than 10 bucks, from China even cheaper.And most will find a soldered on connector on the other end of an old antenna to be salvaged if required.If you don't have any sring steel wire of about 40cm length then think out of the box ;)The packing of pillows and such often come with a sring steel wire to make the plasitc floil keep its shape, some old suitaces have thicker wire doing the same.And if you ask nicely you might get a bristle or two for free from a street sweeping machine at your councils depot ;)After all we only need a maximum of 40cm to have enough left to trim and tune down.What is left to do?Of course some distance tests to check how well such a simple antenna really really works in comparison to commercial models.I only have one 9db antenna and will check it first to see if on flat terrain there is much difference in distance for transmitting.Unless this difference is well above one kilometer I will not bother with a high gain antenna like this anymore and instead opt for a longer mast and 1/2 Lambda.Another thing on the to do list to try a ground plane antenna with topload to squeeze the radion lobe down to under 15°.The resulting antenna would be quite short here and using an elevated mast is a must have to get over roof level with at leat a few wavelengths of distance to the roof.I guesstimate that an optimised antenna of this style should result in a distance increase of about 10-15km of flat terrain while being utterly useless in a hilly areas.Plus, such a design is not really suited for a vehicle going fast on a freeway, so it will go on my house instead.

Topic by Downunder35m 


Different antennas on one mast

I have a standard vhf/uhf/fm antenna on my roof. I live about 45 miles + from the towers. I also would like to get in HD Radio and decent fm stations. Therefore, I bought an Antennacraft FM6 yagi antenna for the roof. Can I place this antenna on the same mast as the tv antenna? If placed too close would this cause interference for either? Any advice would be appreciated. Thanks!

Topic by stacym456   |  last reply


SDR - Software Defined Radio, are you hooked?

Using a cheap USB dongle and an antenna everyone can listen to broadcasts.This includes HAM radio, VHF, UHF, DAB, data servives, satellite communications and even the ISS.Pagers can be listed too if you still find someone using them but getting the latest weather might be nice as well.What are you listening to, what data do you decode?What is you best story in regards to your SDR experience?Prefered programs?

Question by Downunder35m 


RFID - Metal blocking receiver issues?

Please can anyone advise? So we've built a prototype that detects when a bottle is opened And triggers a software response. We need to build the real thing next. The prototype: We've used a small passive UHF RFID tag mounted on the lid of the bottle, hidden under foil. When the bottle is opened this tag pops out and can be sensed. We have a long range RFID scanner that recognised the appearance of the tag and send the signal onwards. This currently works ok at a Distance of around two meters. Problems with the prototype: The action of revealing the tag is not very reliable. Currently we've just experimented with various pieces of tape and foil attached to the tag and bottle. We need to develop something reliable that could be applied to a couple of hundred bottles. The range is a bit shorter than we'd hoped as well - ideally we need the range to be over 5 meters. Our reader has the option of adding multiple aerials though which may help. And perhaps we could have a set of readers linked It's not necessary to use RFID if some other way of detecting when the bottle has been opened could be used instead. The reason we chose RFID is that the bottle doesn't need anything very large added to it. We are trying to sell these things after all. We really could do with someone who can help make this system more reliable Both by helping us with improving the mechanism for revealing the tag and increasing the RFID sensing range

Question by hanspan   |  last reply


MPF102 replacment for a Ghost Detector? Answered

I was gonna build a simple one LED device that can detect a static charge (which in Theory ghosts give off a static charge making the LED to go dim) using this MPF102 FET Transistor, but Radioshack doesn't sell these anymore, is there another different FET that works as the MPF102 FET one? I was gonna try this one http://www.radioshack.com/nte2902-j-fet-n-channel-vhf-uhf-amp-25v/55052700.html#q=FET&start;=3 - but not sure if this would be a great replacement for detecting a static charge like in video saying I need this MPF102 one. Here's the Video Explaining this - http://www.youtube.com/watch?v=ckFAs1i_41Q

Question by SuperScourge   |  last reply


Radio Mod?

I would like to mod a handheld radio (or even a analogue tv but radio would be better) to get to listen to higher frequencies than normally available. I'd Like to hit the 1420Mhz mark approximately but with little electrical engineering or architecture experience, I'm not certain how? Which might make a TV easier to get there as UHF covers that right? (still safer to play with a battery powered radio than a 240V powered one) I figured there is someone out there with the ability to figure out what components need changing? The variable resistor that tunes it perhaps? If you'd rather post an instructable I'll follow that or just tell me what needs replacing with what? Any Ideas?? Thanks

Question by Mr E Man   |  last reply


Mast head amplifier on FPV? Sounds crazy right! Answered

Hi i have been looking at buying this > http://www.hobbyking.com/hobbyking/store/__16457__900MHZ_1500mW_Tx_Rx_1_3_inch_CCD_Camera_PAL_520TVL.html but i thought it might not be very good signal if not i was also thinking of buying something like this http://www.ebay.co.uk/itm/Vision-27dB-VHF-UHF-Masthead-Amplifier-Booster-TV-/220918608294?pt=LH_DefaultDomain_3&hash;=item336fc671a6 It is 900 mhz so i think it is just crazy enough to work i also happen to have an old mast head amp power supply just laying around gathering dust. I'm not bothered about spending 6 quid just to try it out but what i was worried about was feedback from the PSU to the reviver I mean I don't want to blow it on day one how could i stop this and would it be a problem in the first place?

Question by Daniel Deacon   |  last reply


S-Video to RF creates 5" B&W Monitor?

Does anyone know how I could use the RF MODEM which I removed from an old VCR to convert S-Video out (PC) to RF in on an old black and white 5" portable TV?I'd like to use a 5" tube as a small monitor which will hook-up to my PC without lacing it through VCRs cables adapters etc. And if I find my A4 Fresnel lens I want that worked-in too.The pins on the MODEM are labeled (left to right) as follows:(1-7) BB+ AUD SDA MB+ SCL VID VT+(8-13) (none) (none) AS SCL SDA B+ (14-16) TU (none) (none) (17-20) A/O S/O AFT V/ORF in at the top, RF out at the bottom(I also have a large colour TV with UHF SCART & composite inputs, but I think there's a fault with the HT supply to the tube. I have a large CRT colour monitor, but I'm not too sure I want to take that apart.)L

Topic by lemonie   |  last reply


TV antennas and what is possible indoors

Back in my young years a TV antenna was on the roof, quite big and only required to get 3 or 4 channels at best.The basic design of these Yagi antennas has not really changed since then.Same for the antennas required to get UHF and VHF channels at the same time.They either comes as two seperate antennas with a mixer or as a UHF antenna with some added loops for UHF.To talk some basics:For UHF you can get away with quite small dimensions for your antenna bits.After all a quarter wavelengths here is only around 15cm long.With VHF though we get already 30 to 40cm here depending on the channels.So called bradband antennas claim to be able to get a wide range of frequencies.That however is only true for their dedicated frequency band.If you take a normal whip style antenna then this becomes obvious - just compare the lenghts required and you realise "going the middle way" will mean neither UHF nor VHF would get any usable reception.For a long time now there is the option of so called "fractal antennas" to get better TV reception....Fractal antenna? What the heck is that?The theories behind them are about as old as fractal antenna designs that were not even considered to be fractals.Let me explain with the example of a standard FM radio antenna.For them we use frequencies from about 88 to 108MHz.And of course, for our cars they are always on the roof or mounted somewhere around the wheel arches.Some cars however does not seem to have any antenna depsite having a working radio.In this special case rest ensured they do have one, usually behind the plastic bumper bar ;)I like to go off road every now and then and lost count how many times I had to replace my antenna after getting to close to some bushes and trees.As a solution I used some thin wire to create a L-style anteanna on the inside of my windscreen.And funny enough it picks up more stations than a "proper" antenna outside.Really old design and if you think about it then an antenna with a kink that looks like L is ""self similar" - the definition of a fractal ;)More complex shapes like the Sierpinski models do exactly the same just in one more dimension.Cell phones use them as well as you WiFi router that has no external antenna anymore.Their designs and looks are so different that it is next to impossible to list the currently used shapes here.What it comes down to, when you just take a very basic flat or wire shape is that the straight single segment of the active antenna is split into one or many shorter segments that change the angle.They all have similar relations to the wavelenght still.Means really long segments might be half of a wavelength while the shortest bits are just 1/64 of a wavelength.Think of it (far too simple of course) like amny matched antennas combined into a single one.With that often comes a destinct radiation pattern, usually with a quite narrow beam angle that provides a quite high gain.Are fractal antennas any better than for example a proper Yagi antenna?You can ask 100 people and you get 100 different opinions for this one.This is mostly due to some simple facts like:Not caring about actual comparisons.Not being accurate enough when building the fractal antenna.Using just very basic equippment to compare results.For example when you have a 30 year old and quite small TV antenna on your roof and struggle with digital TV reception than you might want to just replace it all.In some case even the old rabbit ears on your TV set will work better.But take modern Yagi antenna with 12 or more segments and even station that are 100 miles away have a good chance.Comes down to possible gain, frequency match and of course how well the antenna is aimed at the transmitter.Then why is it that some fractal antennas still seem to perform so much better?The big antenna scam....If you paid attention during the intial DVB-T rollout in your country then noticed two things.a) You were told you need a TV or set top box capable of receiving DVB-T signals.b) You need a suitable antenna.Well, A is obvious but for B a lot of people got scammed badly.You see, in almost all cases the frequencies allocated for TV signal did not change at all.And an antenna really does not care if the incoming signal is analog or digital - it only cares about the frequency.But more and more local stations often meant that the trnsmit power is limited.After all it makes no sense to have a 500kW transmitter if the area to cover is only about 20 square km big.So people were told they need new antennas once the noticed digital TV is more like playing Tetris, blocks everywhere....You analog TV had no problem with a slightly weak signal, you did not really notice it unless the weather was really bad as well.All the benefits of digital TV however only work with a proper signal strength.If your areas still has both analog and digital TV channels then have a look on how your local transmitter provides the signals ;)Part of the big scam was hiding a very simple fact:All analog TV is transmitted in a horizontal orientation while almost all digital TV is transmitted in a VERTICAL orientation.Ok, we already gain and ignored it but why would the orientation be important?Your radio antenna is vertical because the FM signal is transmitted the same way - the "waves" if you like go up and down like a sine wave.You still get reception if you turn the antenna 90° to make it a horizontal one but you will realise that weak station are no longer available.The same happened with digital TV.And if there is only digital TV left in your area then simple turning your antenna 90 on the mast to have the single elements vertical instead of horizontal gives you top reception again ;)If you struggle to get all station then just try it out before buying a new antenna ;)Modern fractal TV antennas come paper thin and often with rediculous claims in terms of gain and range.On Fleabuy you can even find models claiming to get stations from over 2000 miles away LOLSome even come with the fake claim of being omnidirectional, meaning it does not matter where you place them or how you orient them.A fractal antenna can't change basic phsyics though...High gain mean highly directional or at least with a very flat radiation pattern instead of being more like a sphere.A high bandwidth means you compromise on the gain and/or the phsical dimensions.For example a thin whip antenna is quite limited in the optimum bandwidth while a piece of tubing provides amuch higher bandwidth but at the expense of gain (and some other problems).A fractal antenna can compromise between the two worlds much better than anything straight.And you would even need to make the traces on the plastic extremely wide because you can simply add different lengths for different frequencies.Means a wideband fractal antenna for FM, VHF and UHF basically is three different antennas combined into a single one.It also means that there is usually always more than just one single element of the antenna that is receiving a signal.If you experimented with WiFi antennas for your router or modem than you certainly found the famous Pringles can antenna - highly directional and with an insane amount of gain.Works exactly like a simple directional microphone.And you could, at least in theory do the same with a TV antenna - if there wouldn't be the problem of the wavelenght.A pringles can works for WiFi because the wavelenght only requires an antenna of about 3cm in lenght.You might not want a row of steel drums with a diameter of around 80cm on your roof just to watch the news though...Ok, if I need a new antenna anyway then should I get a fractal antenna or not?I try to make it simple:Roof option not possible or too costly AND your transmitter is not too far away then try one of the cheap paper thin antennas you find online.If you already have an antenna on the roof that is suitable for the frequencies you need then check it to know if it is still any good.With age and weather comes corrosion and some antennas are connected badly in this regard.Sometimes you are lucky and all it takes is to cut off a few cm of cable to get back to clean copper and to give the terminals on the antenna a good fine sanding or a wire brush treatment.In other cases you might find an amplifier under the roof that has faulty power supply ;)And well, certain animals love to chew through your cable...If all is goo from antenna to TV then as said try to flip the antenna 90° to get it vertical.No, I did not mean to point it up to the sky..... ;)I mean rotate it around the x-axis if X is pointing in the direction of the transmitter...

Topic by Downunder35m 


Wireless FM microphone real time voice/play transmitter

Hello I am looking to buy/build a small FM wireless transmitter with built in microphone (similar to karaoke but not exactly ) to transfer voice or sound  from playing  musical instrument  to earphone. It is meant only for practice purpose so does not need  high power, the distance between the microphone (the transmitter ) to earphone  is like from mouth to ear a few centimeters say about  50 cm. I am electronic junior engineer and have knowledge and experience in electronics mechanics and wave buy. Before trying to develop a new product  I was looking for a readymade shelf product. The first way I have searched the internet and reached manufacturer of Bluetooth solutions because of the plenty of Bluetooth earphone that are on the market, but quit a short time after I got some answers from the the Techs engineers  of the manufacturers that Bluetooth will not be my solution because It was not originally designed for true real time transmitting. The main problem is the latency time because there is a delay between the voice or play start until I hear it in the earphone there is improved in Bluetooth 4.1 and 4.2 that is 38 MS and may be not enough while fast playing, So as I was advised I started looking in the RF FM area. FM transmitters are long time in the market of stages and performers, there are high power grate quality transmitters that cost hundreds of dollars. Here is the summary of what I need :        I will need the smallest device (PCB) can be like FM spy bug transmitter. built in microphone (on the PCB ) , built in battery compartment (on the PCB ),built in antenna a copper loop on the PCB (no wire) Since there may be some problems like saturation of microphone or other problems with band width or  sound and sensitivity, sensitivity and control for the Microphone is important. Easy calibration of  tuning and stability , may be digital tuning is better. One option is to use the standard of radio FM 88-108 , but it possible that I can use FM VHF or UHF system that have both transmitter and receiver . If there are no ready made products thatn I can easy build a kit , or from schematic diagrams I will be thank full if you have any ideas. Nevat Ben Haim Recomp Computers

Topic by Nevat   |  last reply


Remotely controlled starship

Hi,I hope this question is appropriate to this forum, I'm new here, but I'm about to start building a PolarLights 1/350th scale Enterprise. If you're unfamiliar with the kit, it's styrene, large and very cool. Get one to express your innner geek.Anyway, I want to hang it using steel wires, painted flat black and it will be displayed against a black background, with the illusion, I hope of it floating in space. I plan to run power to the model via the wires, like those little track bar lights you might find in a coffee shop.All the electronics for the ship will be inside (it's a big kit) and I have the schematics to make the lights blink and the photon torpedos fire. But I don't want the torpedoes to constantly fire. I'd like to be able to push a button and have them fire. But with only three wires going to the model, I can't control the navigation lights, strobes, impulse engines, spotlights, etc.I could install DIP switches in some inconspicuous spot, but how much cooler and geekier to trigger the effects from an infrared remote control shaped like a tricorder?I have found a company that sells a remote (I'll have to hack it into a tricorder), a sensor and a PIC preprogrammed chip to decipher the remote codes (http://kitsrus.com/pdf/k92.pdf), but the schematic shows that all the outputs are high. Pressing a button on the remote sets the appropriate output low.So, can anyone suggest what I can do to trigger the effects? They sell a more expensive and I'm sure much heavier kit with relays (http://kitsrus.com/pdf/k142.pdf) that actually reverses the outputs -- pushing a button sets an output to high -- using inverters. (They also sell a kit with four relays, using a UHF transmitter -- a car remote.)But I'd like to do this without a relay. I know very little about electronics -- just enough to follow a schematic and wire it, hoping there are no mistakes in the schematic. But I thought a transistor, like an SCR thyristor, could be used as a switch. Could I take the first kit I mentioned, add the inverter to switch the output to high when a button is pressed, and use the thyristor to basically be a solid state switch? Essentially doing the work of the DIP switches?I fear the 5V outputs of the PIC module would be too high for the thyristor and maybe that's why the relays are necessary.I appreciate any help and advice.JenniferPS All the kits I mentioned are at http://kitsrus.com/kits.html

Topic by virtualight   |  last reply


Tesla coil antenna?

With the cold and bad weather out there I started again to tinker with my old UHF radio.Trying to build a nice antenna to put on the roof of the hous and such things...While looking up on the various antenna designs I could not help it and followed a few links with antenna designs and specs for all sorts of frequencies.There are things like horizontal or vertical transmission waves or even circular ones.But also some of the basics can be quite different, like whip antennas, dipoles or coiled ones.The later we often see in these keyfob transmitters and receivers for door bells and similar low range, low cost options.Some really old ham radio links got me to the topic or electrically shortening and lenghtening antennas.Things like coils in a whip or added capacitors to match the antenna to frequency and transmitter.A tesla coil usually produces a lot of RF interference, not just on the main frequency it operates on.And from research and physics we learned that for really great distances you need really low frequencies.Like for example the very low bands used for submarine communication around the globe.Here antennas on land can be several km long...The inventor had a few ideas in terms of wireless electricity and communication but I wonder if there is more to it...Despite the broadband EMF a tesla coil produces it is also a really narrow beam antenna.Basically the radiation cone is orientated straight up instead of the usual horizontal patterns we use for communication.The topload again provides a spherical radiation pattern.I am wondering about how a tesla coil would operate as a directional antenna if the topload is replaced with a whip style antenna of a lenght that matches the wavelength...The hip would again provide a more or less spherical beam but the coil underneath would "puch" a directional from underneath.In the classic design the topload is meant to prevent arcing while providing a capacitor so the whole thing is resonant.At lower power arcing is no problem anyways, but what effect in terms of capacitance would a whip style antenna have?Classic pherical or donut style toploads provide little to no gain in terms of antenna properties.If you would use a sphere as an antenna for your CB radio then it would be perfect for very short distance but utterly useless for open range communication.We all know the fun of placing a flourescent light near a tesla coil to show "wireless electricity".Sadly this is more an effect caused by the high frequencies be able to produce the glow in the gas filling.Trying to make an incandescent lighbulb glow is far trickier.Several experiments show that two properly tuned tesla coils can work as transmitter and receiver.But to my knowledge no one ever tried this type of experiment with an antenna on the tesla coil...

Topic by Downunder35m 


12v solar panel/battery setup project- NOT lead/acid

Hi, I have a project that I'm trying to design/build and could use some help/advice with some of the electrical theory. I feel like this should be really simple but I'm having a lot of issues. I have done a lot of googling but can't seem to find applicable answers so I started my own thread. Any help will be greatly appreciated! If I can solve this, I will be happy to write up a detailed instructable so that others can use this information as well.  The short version: Trying to build a lightweight solar panel>battery pack>UHF radio charging setup. Nominal voltage is all 12v. I'm having difficulty regulating amperage between the units. The long version: My friend is in charge of a campsite which needs to have a 2-way radio on at all times. They need to be able to charge these radios on-premise because they are out there for a little over a week at a time. A solar panel seems ideal for this application. The whole charging setup needs to be lightweight since it is a >10 mile hike into the campsite. Ideally, I would like to use an array of NiMH AA batteries because they are small, relatively cheap, and can be replaced easily if there is an issue. I am also under the impression that they handle repetitive charge/discharge cycles well. I am not married to that though so if there is a compelling reason to use lipo or something else, I am open to that. The radio: is a Motorola Radius CP200. The wall charger that comes with it outputs 14v at 1.5 amps. The battery in the radio (according to the sticker on it) is 7.4v 16.21Wh lithium ion. Setup 1 that I've been trying: I have a 12v solar panel charging a pack of AA NiMH batteries. I started with an 8-pack holder but moved up to a 10-pack to increase voltage and total mAH a little. I've been using little voltage regulators in between the solar panel and the batteries as well as between the batteries and the radio. These function as diodes and help me get the correct charging voltage. My problem is that I can't regulate the amperage. The battery pack will pull as much as it can from the solar panel, and the radio will pull as much as it can from the battery pack. What ends up happening is when I first plug the radio into the battery pack, it works fine. But after a couple minutes, the amperage skyrockets to like 3 or 4 or more amps. The voltage regulator hits some sort of thermal protection limit and the whole thing shuts down. I tried throwing this amperage regulator in there as well to keep it below 1.5 amps, naively thinking that it would just affect the amperage and not the voltage. But what happens is when it's in constant amps mode, it just cuts the voltage to compensate and keeps the total power the same. Setup 2 that I've been trying: I thought maybe since I was having issues with the 'smarts' of these batteries charging and discharging, I would switch over to USB battery packs since they have a lot of built-in protection circuitry. I got this solar charger, an older version of this battery pack, and used the same voltage regulators to step up the voltage from 5v to 14v to charge the radio. I get the same issue of high-amperage discharging of the battery pack. I tried using this step-up converter between the battery pack and the radio but it doesn't seem to work or maybe I'm not using it correctly (I can't seem to get the adjustment pots to actually do anything...). It seems like I'm thinking about current wrong or something. Any suggestions or insight into what's wrong with my approaches would be super helpful. If anyone has any suggestions for radically changing my approach, I'm open to those as well. Thanks for reading!

Topic by Cking0987   |  last reply