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SDR radio

I plan to buy SDR radio hackrf one, l like this radio on the foto, is portable not need a computer to work, operative range up to 6Ghz. I want to ask is there a device which to increase the operative range at least with 10Ghz? (or can tell me from where to buy SDR radio hackrf one, capable of transmitting with high operative range on low price)

Question by Viktor Karadzhov  


SDR antenna - 50 or 75Ohm cable?

Once you get going with your new SDR dongle you soon realise that it is little fun with the supplied antenna - if it came with one...Local stations, police (unencrypted) and so on is all fine with the short antennas.But if you want to get weaker stations or even track some satellites you are as lost as trying to get anything in the 160m band on your screen.Obvious way out is to get an external antenna.Depending on your needs and layout at home you might be lucky to find a ready to go option at some cost.In most cases though you will need more than the 3-5m that come with the usual antennas for car use.And not all base station antennas come with enough cable - keep in mind that hieght above ground and no obstructions close by count...With RG58 cable already being quite expensive a lot people consider the cheap 75Ohm TV cable as an alternative...Can we use 75Ohm antenna cable for our SDR needs?Of course we can!We only need to make sure that at the antenna end AND the receiver end the cable acts and appears like a 50Ohm cable.Especially if you need a really long cable in range of over 20m the TV cable shines with less loss that can't be ignored.Let me try to explain it the simple way first:You TV needs 75Ohm but the good old dipole antenna provides 300Ohm.The so called BALUN that connects the actual antenna with cable matches the antenna to the required 75Ohm impedance for the cable and TV.Like the TV, we don't transmit anything, so we don't have to care about what happens if power would go to the antenna - it is not a radio in the common sense, we just listen ;)There are many options available to match any impedance to any other but in our case a lenght of coax pairs is all that is needed.1/12 of the wavelength for the 75 and 50Ohm cable and we have a match.But.....You are right this simple option does not really work if you want to listen to a lot of different frequencies.What works fine for the TV also works fine on both ends!I assume you use an antenna for the common 50Ohm system and a standard 50Ohm SDR module or receiver.Two simple transformers will do the trick just fine and allow us to use cheap 75Ohm TV cable.The one on the antenna end provides 50Ohm for the antenna and 75Ohm for the cable.For the receiver the transformer is the same type but connected in reverse.You can look up how to make one with a simple ferrite torioid core and wire or coax but also order them from your favourite Chinese seller in the usual online markets.Add an antenna switch and you can use multiple antennas optimised for the frequency in question with dirt cheap TV cable.Just make sure to put the balun in a metal enclosure that is connected to the braid of the coax on both ends.

Topic by Downunder35m  


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  


Decoding and understanding what your SDR scanner is receiving!?

For some reason, every time I upgrade my antenna I get more signals on my screen that I fail to decode or even understand.When I started this hobby it was mostly about voice transmissions and trying to get radio stations from overseas.Now I am starting to wonder what is behind these endless amounts of transmissions that my software fails to decode or recognise.Some things like TV, pure data or trunked system like the P25 are usually not a problem to identify.An awful lot though is not recognised at all.Also found quite a few signals that produce sound that just isn't right.No matter what type of audio is selected thest I describe these sounds is like weird space sounds with a lot of echo in them.Like a base tone that goes up and down in frequency and is overlapped by blips and beeps.I am not good at all with Linux.You could say Linux and I are like a cat and a dog locked in the same room ;)So I only used the common programs available for SDR decoding use that work with Windows.I guess my question would be:Is there a software out there that can identify the received signal automatically?You know, if doubt be routing the audio to it and getting something back like "Encrypted P25, LoRa data, DVB-T,....".And for whatever is not recognised directly at least something to help identifying the signal.A lot can be done by just researching the frequency allocations.At least down here they are quite strict and that means if you find some info that a certain frequency is reserved for data transmission on short range you can tick them off.The ideal thing of course would be something that works automatically as a complete packet.But I guess that will be a few more years till we get that pleasure :(

Question by Downunder35m  


Cloning the famous ARA-2000 antenna for SDR use

Several years ago the company behind the original ARA-2000 antenna, Dressler Hochfrequenztechnik, closed.The ARA series of antennas, like many other products by this company never got a patent, instead it was trusted that no one would bother to replicate it.A bit like the Swiss Army knife, many tried to copy it, none really managed to match the original quality.There is quite a bit of hacking still going on for this antenna, most projects though seem to be abandoned at the time of writing this.I am currently trying to figure out how to create an entire clone that everyone who knows how to properly use a soldering iron can build.There is a lot to consider here...The active element is of quite unusual shape and needs to be wound around a cylinder of a pretty accurate diameter.My initial tests showed that for example aluminium foil with some unavoidable wrinkles already has a negative effect.And a change in diameter of just 2mm means the entire antenna only performs badly for the entire band.This part is thankfully already solved to my satisfaction using thin copper sheets and some stiff plastic sheet.Quite a pain though is the MMIC part - the amplifier that makes the antenna active.There is a ton of MMIC blobs available, either solo or as a ready to go amplifier.Downside is that without really knowing any characteristics of the original is comes down to guesswork.And as most of the cheap SDR dongles won't provide a BIAS TEE I will opt for an external power supply for the amp.I might provide the option for a inline use a bit later though.Why clone the ARA-2000 antenna?For starters you need to forget the mythical stories you might have heard about this antenna."Picks up even the weakest signals!", "Totally linear over the entire bandwidth" and so on...Without the amplifier the antenna is actually not even average in therms of reception performance.My initial tests with a network analyser showed that the anteanna actually is behaving really weird (without the amp!).Although this first bit needs further testing, it seems that most, if not all of the work in the 1.5-2GHz range is done by just the straight connecting strup going from the amp, or in my test case the coax, to the wrapped antenna part.For anything in the more interesting frequency bands it seems that the antenna is not using anything like a discone, whip or ground plane antenna.Instead the 3rd harmonics of a given frequency provide the max power output from the antenna but it arrives at the cable at the right frequency.Especially in the lower frequencies, below 200MHz there is also quite some phase shifting happening.As a passive antenna it seems to be almost impossible to find a frequency to transmit on without using some matching trickery first.But when it comes to size or looks, the ARA outperforms everything you can think of unless you want to constantly adjust the length of your whip antenna.And if you check what is available in real (user) data in terms of noise and signal quality than most other antenna types are far worse.The design provides a wide frequency range with very little noise, almost like a build in filter.Considering that mostly harmonic frequencies are used not that surprising.Getting hooked on SDR means you start little and then you want more and more.Unless you really need the low frequency HAM bands below 50MHz the ARA is a good choice that just makes sense.What is quite surprising in the original is the total lack of protection for strong signals.Sure, we might never need a lightning arrestor because all is enclosed in plastic and has little attraction lightning, but someone hittiing the transmit button close by....I will have to do some more checks to determine whether or not more protection is required.What is the problem with amplifier?For starters, no one really knows what was used in the original - they all just guess based on how well the real design matches some datasheet.Means whatever was used might as well be a custom made solution.I checked a few datasheets for MMIC amps but could not find any useful reference to the handling of things like negative gain, phase shift or a constantly changing impedance.Some however state that a 50 or 75Ohm signal is provided at the output.If I interpret that correctly than those MMIC's not only amplify but also do some matching.In most cases you won't need an amp that works outside what the antenna can provide.Problem is that I don't like regretting things later on ;)So IMHO it would be best to use a wideband MMIC covering all from about 1MHz to a few GHz.Additional filters can then cut off what is not required or where the antenna starts to fail.What is clear by the original design is that the cable shield acts as a ground and most likely also has a balancing function.It would make sense to add a ferrite trap close the the receiver to filter out what the cable might otherwise mess up.Can the frequency range be lowered to get even the low HAM bands?The answer is YES and NO.It is not a big problem to extend the cone shape and then hope to come much lower.Issue with this is the helical, long periodic design.As basically only the 3rd harmonics are used for all interesting frequencies any ARA type antenna going much lower would end to be really long.You can't just make it longer!One thing is to have a full and even number of turns.The original only had two, three turns is bad, four means the entire antenna is slightly longer than your average downpipe for your roof gutters....Other, seemingly logical alternative would be to stick to two turns and to increase the diameter.Apart from the size problem here we would also change the shape of the foil quite a bit and I have not done enough tests with that to provide a conclusion.Are there alternative design options?As it turns out copper pipe is available in 80mm diameters for the use in chimneys as well as downpipes.With a proper machine it would be pretty straight forward to remove what is not used as the active element.Milling a pipe or rod is these days a common thing in many good workshops.But on a hobby level and low budget....One of the best options for cheap test antennas of this design is to use tinting foil - the cheapest you can find ;)Just read the lable and make sure it does not use a metalised film.If it has no UV protection and no tinit at all it is best but hard to find.A little less stiff is the stuff to cover school books or cupboards.Vinyl is bad though!If you look for copper foil in the cheap online places you mostly find the suff used for shielding in rolls of 200x1000mm.Unless you have a really sharp knife or really suitable sissors this stuff is a pain to cut as the glue tends to stick very good to whatever you use to cut through.Don't ever try one of these blade type cutters for paper and pictures unless you put a slight oil film on all cutting surfaces first....In some hobby shops you can get copper foil without any glue in different thicknesses - this stuff is the prefered option.Not only cheaper than the China rolls with glue but you invest a bit more and get a thickness that does not wrinkle right away when working with it ;)Cheap, steel downpipe and cutters or nibblers?I though about and I tried - and I failed LOLUnless you use a pin type nibbler and custom made rig the result is quite bad - at least mine was.What works though is to use thin aluminium sheets, cut them and then bend them around a suitable template.But I ran out of old laminated sings to salvage and the duble sided ones I have left are too much work.What comes next?Well, I have a few rolls of copper sheets coming next month, the cheap glue covered type.This time however I will leave the plastic cover on and use tape to secure the foil to the pipe.A two-stage amp with external power supply is coming too so I can do some more tests in this area.For the time being I will opt for some 3D printed end caps but with a bit of luck can find something easier next time I have time to waste in the hardware store.Excluding cable and a cheap USB or 12V power supply, the current costs of building the anteanna are around $40US.About half of that if you don't cennectors and attach the coax directly.Another experiement I am working on is to use copper tape, 12mm wide, to create the antenna in a semi-fractal style.I am hoping this will provide a high enough gain so the antenna is usable without an amplifier.Right now the biggest issue is to find a really SDR suitable way to deal with strong signal close by.I will keep you update here when I start with the new antenna and upload some pics along the was of building it.

Topic by Downunder35m    |  last reply


How to change a 433.92 MHz signal in to a 434 MHz signal?

Hi,I have these remote controlled wall outlets (Brennenstuhl Funkschalt-Set RCS 2044 N Comfort). And I'm trying to make an arduino circuit with an RF transmitter so I can switch them on and off without the remote.I sniffed the signal from the remote with an RTL-SDR and found out that the signal frequency is 434 MHz. So I went online and ordered an 434 MHz transmitter (from sparkfun).After I hooked the transmitter to my arduino and wrote the code with the exact same signals as the remote had send out. I tested the circuit and saw that it didn't work.So to see where it went wrong I also sniffed my signal from the RF transmitter, to see if it's the same as the one from the remote. And I found out that the frequency of my 434 MHz transmitter is actually 433.92 MHz.But this turned out that it wasn't a mistake. But the chip in the datasheet even says that it is 433.92 MHz. And when I went online to find a real 434 MHz transmitter I couldn't find one, because all the 434 MHz transmitters that I found were also actually 433.92 MHz.So then I tought how the hell has my remote a 434 MHz transmitter if I can't find one? And I screwed it open and saw in the casing that even the transmitter of the remote is 433.92 MHz. But for some reason it sends out a 434 MHz signal. So it must have some kind of circuit inside that modifies the 433.92 MHz to 434 MHz.And now my question to you is: How can I do that? How can I modify a 433.92 MHz signal to a 434 MHz signal?Thanks in advance!(I uploaded some pictures of the remote, the wall outlet, the RTL-SDR, the RTL-SDR captures on my laptop, The (simple) arduino circuit and the transmitter module)

Question by piet_lu    |  last reply


Can I use a security cam dvr to record my tv shows?

I found a working(turns on) digital video recorder with a hard drive in it. Can this be used to record tv shows off my smarttv? It's a Samsung SDR-B74303n, it does not have a remote. Any advice appreciated. Thanks.

Topic by LoriR76    |  last reply


Decode Custom RF ASK Signal with Arduino & RadioHead

I have a remote that sends out a preamble, a pause and then a long code where a 0 is encoded as 100 and 1 is encoded as 110. I used an RTL-SDR to decoded the aforementioned ASK signal. I know the code is correct because I can simulate the signal using an Arduino and FS1000A. I simply connected the FS1000A's data pin to a digital pin and then I send out the signal. What I want to do is actually receiving the signal on the Arduino, i.e. which button was pressed on which remote (there are multiple remotes). For that I am using an XY-MK-5V and the Radiohead library. I used the RH_ASK driver sample code. However, it doesn't receive anything at all, meaning nothing is printed to the serial monitor.I think there are a couple of issues, i.e. it seem the Radiohead library expects a different preamble then what my remote sends and it also expects a checksum which my remote also doesn't seem to send. I haven't found a way to configure Radiohead so it can deal with my remote code. Is such a configuration possible. If not, what are the alternatives?

Topic by muludu