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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  


Neon-Nightlife-LED-Light-Up-Glasses

I am looking for a flat pattern to make the plexiglass part, I can bend these after engraving and do the LED myself , so does anyone have a pattern for something like these, the way its curved https://www.ebay.com/itm/Neon-Nightlife-LED-Light-...or something similiarThanks

Question by MRX2099    |  last reply


LEDs from ebay? Answered

Is ebay a reliable source of LEDs? I bought a 3 watt LED off there once (http://cgi.ebay.com.au/3-X-POCKET-LUXEON-3-WATT-LED-TORCH-FLASHLIGHT-LIGHT-3W-/320514643442) and it had kinda poor performance...but I don't know whether it was because the torch itself was poor or if the fact that buying it from ebay was what made it bad. Any how, I'm looking for a 1 - 3 watt LED, and a (narrow beam) lens for it, and was wondering where I could get it all for under $10 (AU). WOuld ebay be a reliable choice?

Question by .Unknown.    |  last reply


HOW TO BUILD OR WHERE TO BUY CHEAP & SIMPLE AUDIO HARDWARE?

I am looking to buy the INNER hardware for a small/cheap recording device. I just need the hardware to record 30secs of voice audio. I do not need an outter casing for the hardware as I am making my own case for the hardware. Nothing fancy just cheap & basic. HELP!!!!!!!!! Thanks! Tracey

Question by fire1973    |  last reply


how to bypass a password on an nec lt280 projector?

Hi, have purchased a second hand nec lt280 projector, have tried to use, but is password protected, i asked the people i bought it from, they said they dont have password, asked nec, they wont help. When i turn projector on it asks for password straight away, i cant get any further, can anyone help?  Cheers....

Question by rgr.jenkins    |  last reply


how can i make something crispy in the microwave ?? Answered

See i was trying to make mini egg rolls in my microwave and they came out kind of soggy and didn't taste as good as they do when i fry them or bake them so i wanted any ideas on how to make things made in the microwave crispy?

Question by json12795    |  last reply


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  


How many amps does a 9 volt battery put out?

I am trying to run a portable DVD player off of a nine volt. Is it even possible? Thanks for the help guys...

Question by ElectroFlex    |  last reply


Simple battery charge level indicator? Answered

I need to be able to see the charge level of a 12v rechargeable battery and want it to be as simple as possible. Would this setup work: 3 zener diodes (at different breakdown voltages 10, 11 and 12 volts for example) with cathodes connected to positive so that when the battery was above their breakdown voltage an led could light up. Here is a diagram:

Question by Scytheon3    |  last reply


how to build bluetooth device?

I wanted to turn on/off the LED light from my bluetooth enabled cell phone and building cost can be around $10, not above $10 :) . Is it possible?

Question by chandan45600    |  last reply


Best Method to Attach and or Sew Feathers on to Clothing or Fabric? Several methods are needed.

I am looking for several methods of attaching and sewing feathers to clothing. I want to avoid using glue if at all possible, or perhaps a combo of glue and needle? Examples might be edging of cloaks, collars, cuffs, etc. Anyone have any neat tricks or ideas?

Question    |  last reply


Are you going to ISTE?

Anyone going to ISTE this year in Philadelphia? Is there anything you are excited to see or do there?Instructables will be at the Autodesk booth along with our friends from the Tinkercad and Fusion 360 teams. Come find us and say hello, and learn about some of our new teacher-friendly features. You can also decorate a tote bag and grab some cool swag!

Topic by randofo    |  last reply


i need to make 150$ in two days please help!!!! ?

I need to make 150$ in two days but i am to young to get a job

Question by bobbambusle    |  last reply


How to turn on a 24v solenoid when a 110v unit is shut off? Answered

Ok, so an odd ball scenario. I need to open a 24v solenoid(lawn sprinkler valve NC) for 5 minutes after main power(110v) has been shut off to a device. I have the ability to piggy back on all the power terminals, so it could have constant and switched power. I feel like this kind of thing will exist somewhere, I just can't find it at a Home Depot, and can't seem to google the right key words. Thanks to anyone who can point me in the right direction!

Question by Hack/Slash    |  last reply


Website-BUG: Login-Cookie-Handling over multiple PCs with feed

I had this problem in the past sporadically but never saw a pattern till recently:I come to instructables.com, i am already logged in and click on "feed" at the top.After a while an error pops up telling me a Rerouting-error happened. (Umleitungsfehler in German).I noticed, this always happens after the following action-pattern:- I visit instructables.com and log in on computer A and i DONT log out there but only close the browse.- I visit instructables.com on computer B. I am seemingly already signed in from the last visit here on Computer B at instructables.com. - If i now click feed (On Computer B), the error happens.- If i logout and log back in on Computer B, the error is gone on this computer B, even over Firefox-restartsAs far as i undestand, as soon as i log in on computer A, a new login-cookie is created on Computer A and the cookie on Computer B will no longer be valid next time.Now, if i come to instructables with computer B, the cookie somehow still is interpreted valid and logs me in (I appear to be logged in with my avatar visible at the top right). However, if i want to go to my feed, it seems Instructables checks again the cookie and figures out that i have a no longer valid login-cookie on this Computer B due to my login on Computer A and refuses to redirect me to my feed. This gets sorted with Re-Log on Computer B, creating a NEW login-cookie on Computer B and all is well again on Computer B. Now i can play the same game on Computer A with re-log. :)I hope, this error-report helps you guys in pinpointing and fixing an issue with a Login-bug as it seemsAnd Why to hell do i have to define in which channel this belongs and you dont have a channel "website of Instructables"?!? I hope this is not lost in "Circuits" - "Software" which was the closest i could find to a website-problem... Geez...

Topic by Orngrimm    |  last reply


Wind turbine to charge batteries

I have a solar electric system with a battery back up for power outages.(it is also grid tie) I would like to add a wind turbine to charge the batteries in extended outages with no sun and hopefully wind ( we normally have low wind but storm outages have lots of wind). The batteries are 12 volt connected in series to produce 48 volt. Can I, should I, get a 48 volt turbine and connect direct to the batteries or some other voltage and go through the inverter like the solar panels do and if so how and what voltage turbine?.. Chris

Question by papabear911    |  last reply


Box light from broken monitor

Hi, this is my first DIY project! I'm trying to convert a broken monitor into a panel light. I've successfully taken it apart, removed the LCD portion and retained only the backlight (with diffuser), which works fine. However, I have no idea how to keep the backlight on without a signal on the DVI/VGA ports, which the monitor's circuits clearly expect. When I press the power button, the backlight switches on, stays on for about 30 seconds and then switches off, presumably because there's no signal from the VGA/DVI ports.Model: T215HVN01.0Data sheet: https://datasheetspdf.com/pdf-file/789046/AUO/T21...What do I need to do to keep the backlight on as soon as the power is on? I have all the necessary tools (wires, breadboard, assorted resistors and capacitors, soldering iron, etc.). Do I need to have all the circuit boards that came with the monitor, or can I somehow make do with just the yellow board which takes care of the current and voltage to the backlight LEDs?I'm putting some pictures of the circuits here for reference... If I need to zoom in/focus on any specific part of the circuit boards, please let me know. Hoping someone can guide this electronics noob. :)

Question by MisterFrostee    |  last reply


33cc Gas GS Moon Scooter Help? Answered

Ok, I already posted a question about this. The problem was a mislabeled sticker. Now I have more problems. The problem this time is my dad just randomly came out and started adjusting the idle screws for high speed and idling. It will now not run. I am not sure if he adjusted anything else but I need a bit of help. The engine model number is 1E36F 2-stroke 33cc engine and this is a GS Moon scooter. It has a full tank of gas/oil mixture which is correctly mixed yesterday.

Question by Electric Spectre1    |  last reply


Power lamp or LED by POE

Dear all,I have an HP POE switch. I can power up a Camera, CISCO phone & AVAYA IP phone.I am wondering if there is a way to Power UP a bulb or small LED via this POE switch please.

Question by samerrustom    |  last reply


Pop rivet stem removal? Answered

I need to use the pop riveter today, but there is a leftover 'stem' thingy stuck in it. I've removed the nozzle (?) and squeezed the handle a few times. but it's still stuck. I've tried pulling on it with pliers with no success.  

Question by mole1    |  last reply


Connect several DIY Bluetooth speakers

Hi peeps, I'm looking for Bluetooth (BT) amplifiers that can sync with a connected music device, for example an phone, so the music played from the phone will be sendt to all speakers. Hope my question are understood, and would greatly appreciate your feedback :)

Question by KayOeS    |  last reply


Change yarn colors ?

How do I change yarn colors in crochet With pictures?

Topic by Godloveus1962    |  last reply


Pathway?

I want to make a short walk way from the crappy patio, which I would like to change for decking, to the shed. As you can see I have pallets and I can get many more for free. So would like to utilize them How would you go about it?

Question by CarlH78  


PS2= multimedia server with windows?

Hello Everyone,My questions is as follows. My friend has an old PS2 collecting dust, dying to be cleaned and given new life. Sadly, i'm not much of a gamer and this console is out-of-date as of this writing. I read on some other websites that you could turn it into a multimedia server. There were two versions: the Windows one and the Linux one. The Win one disappeared from the web for whatever reason, and i'm not tech-savyy enough to play with Linux -- i'm an initiate as advanced pc user but nothing more. So my question to you is: do you think/know of a way to breathe new life into this console and unleash its multimedia center potential? Sound off in the comments!!

Question by Mad_Dog77  


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  


Fun with firecrackers?

Does anyone know how to have a lot of fun with firecrackers, in a weird way kinda, other than putting them in bottles and throwing them?check out my youtube

Topic by halzep    |  last reply


Unfollow

How do you unfollow members? I accidently pushed someone's follow button and I don't want to follow them.

Topic by MissSongbird    |  last reply


Electromagnet Help! How to Make a Small but very Strong Electromagnet???

I need you help smart people of Instructables!I need to make a small Electromagnet, that uses minimum power (by that I mean the battery), but still has to be very powerful. I have a couple of questions that I need you to help me answer:Does the number of coils that is wound to the metal bar effect the strenght of the electromagnet?Does the wire gauge (20,24,28,30,34,36 wire gauge) make a difference is the strenght of the magnet?Does the voltage I supply to the coil effect the Electromagnet?What type of battery is best for an Electromagnet (AA, AAA, C, D), and what voltage (1,5V, 3V, 4,5V, 6V, 9V) ???Here is the thing, I need to make the Electromagnet super strong but taking up the minimum of energy, for example, just 1,5V. The things that are not important to me (doesn't play a factor in my device) is the number of wire winds to the metal rod and the wire gauge! So is it better to just make 1 or more (3,4,5,6...) layers of wire winds???Is it better to use thinner (36 gauge) or thicker wire (24 gauge)???Thank you a lot!Stanislav

Question by comodore    |  last reply


What Is The Best Pranks For Summer Camp?

I am going to summer camp for 10 days and I need the best pranks in the world. Give me them all.

Question by Thelonelysandwitch    |  last reply


Is there a web site for mini mill engraver users?

Is there a web community out there that will have answers to some of the obvious questions that are going to arise when someone gets one of these machines? It has been a real dog fight to find any info on fine tuning these machines. Some of them are confusing to say the least. I am not talking about G or M code, I am talking about machine specs. Setting micro steps for better resolution. Fixing known problems with various machines, that kind of thing. There sure needs to be one somewhere.

Question by dannybush04  


Condensed soup or not?

Im making a vegetarian version of the recipe below.Its a casserole - type dish and calls for 2 10 oz cans of cream of mushroom soup to be added to the rest of the ingredients.It does not make any mention of using condensed soup, just says 2 10oz cans of cream of mushroom soup.Just curious for those have made this type of dish to confirm one way or the other as to what to add.

Question by jamesbowers    |  last reply


ausome inernet games?

Im looking for some ausome internet games

Question by knexsuperbuilderfreak    |  last reply


how do i bypass onstar to pair up my bluetooth with my car. my car is not bluetooth campatible according to onstar.

I have been told that there is a way around onstar, even if my car isn't bluetooth compatible. if this is true, can someone tell me how to go bypass onstar?

Question by jlm7197    |  last reply


Makey Makey Community Hub

We are stoked to be part of this new teacher community! Thank you, Instructables! We are going to have our own community hub soon, and are hoping you'll want to be a part of it! Do you have a Makey Makey guide that you've created for your classroom? We'd love to see it and share it on our hub! Share a link in this topic to show us what you've made.

Topic by MakeyMakey    |  last reply


whats the best way to open a laptop's ac adapter?

I have a Compaq v2000 laptop with a faulty lead inside the AC adapter's strain relief. I want to cut the cable and resolder it inside the adapter, but I need to get it open... it appears to be heat sealed (no visible screws, but a recessed plastic seam) what is the best way to open it up? btw, I'm quite comfortable working with large capacitors, before you ask. help?

Topic by gschoppe    |  last reply


What's another name for a rotary pneumatic indexing valve?

I am trying to find or create an air indexing or selection valve that has one line going in and several (6 to 12) coming out. I can imagine how to create such a thing: A valve disk that rotates in a body with 6 to 12 outlet fittings on the valve housing. The disk has one hole cut radially and one cut axially intersecting it at the center. Install in the valve body, spin it around with the valve stem, and there you go. Agitate away!The thing is, I'll bet these already exist if I could find them. Can anyone tell me what this thing-a-ma-bob is called? Or who might make them?

Question by cmblocker95    |  last reply


DIY Scuba Tank (breath underwater)

I need some advice. I have a great idea that would be amazing if it worked. I want a small scuba/air tank whatever you want to call it (like a scuba secondary tank or a paintball co2 tank) that i can use to mess around with in a pool. I dont want to be constantly breathing, just enough to take a deep breath, go underwater and hold it for a minute, release air from the tank-take a breath, hold it, take another breath from the tank, hold it, and so on. Just enough to get a few breaths and be under water to last me for 5 or 10 minutes. The only thing is i dont want to have to fill it at a dive shop or from a tank that has to be filled at a dive shop like scuba secondary tanks. i want to rig it to fit a bike pump (which probably will not have enough psi to get the amount of air i want) or my air compressor. So i would like advice and also would i need an air regulator since im not constantly breathing? what could i use as a regulator if i need one at all? 

Topic by wdemarche    |  last reply


What would be the easiest way to hand-make an enclosure for a neon sign with a complex shape?

I want to make a rather small (less than 1 ft/sq) neon sign with a screen-printed plexiglass front, in the style used on the outside of stores (see attached image). Initially I'd considered just making a simple wood box, but for what I'm going for I need to make some more complex shapes, such as starbursts or clouds. Would I just get a strip of aluminum and bend it into shape, then seal the ends together, then just glue in the laser-cut piece of plexiglass? Thanks!!

Question by tim_finnegan    |  last reply


How do you cut open a jack fruit

I bought a jack fruit that has been cut in half, how do I cuy it up ?

Question by anthelzy55    |  last reply


how do i set a booby trap to find out if someone has been in my house?

I gave my neibors my keys and i think they made coppies and have been coming in my house while im not here. things have gone missing, i want to know how i can set a trap that will enable me to be certain that they have been in the house, and that its not really just me loosing things. i want the traps to be set up in a way that i will know for a fact someone has been in my house, i have one idea already i have ties a lot of my hairs together and tapes them accross the hallway and i will see if when i get back home it is busted. please help me with this, i dont want to go to the owner of the building, or to the athoriteis with out knowing for a fact, and i am unable to get a video camera to record while i am gone.

Question    |  last reply


Premium Code

I received a code for a premium Teacher membership.  I have entered the code and logged in, but when I go to download it says I need to upgrade to premium.  Help!

Topic by Zilhaver01    |  last reply


Q: how to ´mute´ the video on a tv-set? (most simple solution)

Hi, i have very little power up here in the cabin and have to watch pretty much any watt. i also watch a bit tv (small set). but most of the time i´d like to use it as a ´radio´ (sound only). is there a quick and dirty way to add the option/function to turn off the video (like i can mute the audio)? a way to configure the remote?, to re-programm a button?, to phyically insert a small switch in the tv-housing?, etc etc?feedback and any idea, no matter how wild, welcome.bowing.

Question by la xerra    |  last reply


Q: input/output-wattage of poe adapter

Hi, i found an ubiquiti poe adapter 100-240v .3a input. here the q: the output is 24v .5 amps >> shouldnt the input/output-wattage be about the same (not considering losses due to conversion, heat etc)? i am confused (but then: i´m usually always, haha)bow.

Question by la xerra    |  last reply


Q: flower-pot mounted in plastic bottle partially filled with water

Hi, i have major water-issues here in the garden (steep southern slope in the mountains; little earth:; hot in the summer). so i always play around and look for solutions. latest play: i cut off a bottle, filled it with an inch of water, and then, a couple inches above inserted a flower-pot that tightly fits. q: is there a chance that the roots will eventually feed of the ´tank´ at the bottom of the bottle so that no waterinbg of the flower(pot) is needed (sort of a self-contained system)?bowing (flower, too)

Question by la xerra    |  last reply


How can I modify a PIR so triggers faster, and then fades out?

I want to make a motion-activated light that turns on immediately when someone walks by for about a second, then fades out for about one second. Most PIRs seem to stay on for a minimum of 5 seconds, then just cut off. I'm looking for a quick burst, quick fade. I'm very new to working with electronics, but my guess would be that instead of modifying the PIR itself, the PIR would be triggering something else that would be doing the timing/fading.

Question by tim_finnegan    |  last reply


solar light to laser beam ?

Hello, would it be possible to concentrate solar light so to form a laser beam ? In other words would it be possible to apply laser light principles to basic solar light with the help of optics of some sort ?

Topic by gabdab    |  last reply


Drafts

I've been struggling with Drafts since the update. I have lost all my drafts, although it still shows them as there, and every time I click on my drafts, it takes me to the homepage. (www.instructables.com)Does anyone else get this? or have a fix? I've cleared instructables cookies, and it makes no difference where I try to access my drafts from.

Question by memestra    |  last reply


Is it possible to connect an led in parallel with a lock mechanism?

I am working on a project. I have a keypad panel that unlocks a door and I want to add in the circuit an led indicator(when the lock is released I want the led to turn on. When connecting the lock with the led in parallel the keypad does not work properly. The lock uses 1amp and the led needs less than 350ma. Would a resistor on the led solve the problem? If yes, what resistor should I use? (it's obvious I don't know much about electronics but I wish to learn...). Any ideas or ideas or advice is most welcome! Thanks community!

Topic by DimiLa    |  last reply


Hi any body know arduino compatible soil ph sensor and salinity sensor?

Hi any body know arduino compatible soil ph sensor and salinity sensor?i'm looking to developed a soil ph meter and soil salinity meter. please help me friends.

Question by Rangam3    |  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