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$20 Spectrum Analyzer for Testing FPV Systems


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#1 Mr.RC-Cam

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Posted 22 December 2012 - 11:08 PM

SDR (Software Defined Radio) technology is sweeping the ham radio community. Until recently the radio hardware was expensive. However, a bright fellow discovered that the PC-USB based DVB-T TV dongles could be turned into a very sophisticated SDR type communications receiver and the ham radio community created software to do just that. Keep in mind that these TV dongles sell for about $20 from a variety of retailers. To learn more about SDR, just google SDR DVB-T and enjoy a week's worth of reading.

So maybe you aren't interested in a affordable SDR ham radio, but don't go away just yet. I think that eventually every FPV'er wishes for some affordable test equipment that can check their transmitter's frequency, measure the relative performance of their DiY antennas, or check other RF characteristics of their video system. And they don't have $10K for a good working used spectrum analyzer. But how about $20? No doubt you are interested now!

Here's a desktop video I made that introduces the DVB-T hardware and SDR# software as a spectrum analyzer for FPV hobby use:
Click For Demo Video
If the above link is not working then try this one from YouTube

 

sdr#.jpg

But there's some limitations. The DVB-T TV dongles support a wide 64MHz to 1.7GHz RF range. So if you are using a 900Mhz to 1.3GHz Video link then you are in luck. Unfortunately the 2.4GHz and 5.8GHz video system can't be tested with the $20 SDR.

So if you are interested in "building" a $20 RF spectrum analyzer then begin your adventures by visiting this site and review the list of compatible DVB-T USB dongles:
http://sdr.osmocom.o...ac/wiki/rtl-sdr

For the record, this is the DVB-T hardware I bought and I am very happy with it:
http://cgi.ebay.com/...em=150808426646

dvbt1.jpg

You will need the SDR# (pronounced SDR Sharp) software, which is a FREE download. SDR# is available here:
http://sdrsharp.com/...x.php/downloads
FWIW, I'm using SDR# Stable, revision 1000.

Installation instructions: http://www.atouk.com...id=MS5ob3RsaW5r
Towards the end of the document is the installation instructions. READ THEM TWICE, then read them again. The installation requires downloading additional files:
http://sdr.osmocom.o...WithDebInfo.zip
sdrsharp.com/downloads/sdr-nightly-rtlsdr.zip

I recommend using zadig to install the required USB driver:
http://sourceforge.n...160.7z/download

You may become a bit confused about getting it installed and working. Go back and read the instructions again, since all the required installation information is documented in them. When you get it working you can start learning to use SDR#'s features and eventually begin using it for test/evaluate your FPV transmitters and antennas.

Here's a link to the quickstart instruction manual:
http://www.atouk.com...QuickStart.html

If you are using a SDR DVB-T for testing your RF gear them share your test setups here. No doubt your tips will help the FPV community.


Edited by Mr.RC-Cam, 27 April 2013 - 05:22 PM.
added youtube link

- Thomas

#2 Mr.RC-Cam

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Posted 23 December 2012 - 06:59 PM

I should point out that the DVB-T dongle does NOT need any hardware modifications. The only nuisance is that its antenna connector is the European PAL type. I had planned to order a SMA-PAL adapter from eBay. But since I had no use for the magnetic base TV antenna that was included with the dongle, I cut its coax cable and re-terminated it with a SMA connector.

dvbt2.jpg
- Thomas

#3 Terry

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Posted 24 December 2012 - 12:28 AM

Has anyone made a converter for the higher frequencies? I guess it would need to be very wide band!


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#4 Mr.RC-Cam

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Posted 24 December 2012 - 08:55 AM

There are indeed some SDR solutions for 5.8GHz, but I haven't spent any time checking them out. I did a quick search and within seconds found this:



Maybe the details there will help you devise a 5.8GHz SDR using the DVB-T (or similar) hardware, otherwise dig in and start searching. Be sure to share what you learn!
- Thomas

#5 Devonian

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Posted 02 January 2013 - 01:30 PM

Well, you got my interest!

I found what I believe to be a suitable USB stick on eBay UK and ordered it earlier today.

 

Googlin' around, I found that the RTL2832u & E4000 tuner stick is now an 'old' product, superceded by a RTL2832u & R820T tuner.

Youtube has several examples of the difference, mostly in favour of the R820T tuner.

We'll see what turns up at my doorstep.

 

I have an immediate use for it as a Spec-An for testing OpenLRS/HK OrangeLRS tweaked for 459MHz.

 

Failing that, it might be useful as a scanning tool at our clubs next 50MHz contest with a pair of 9 ele Yagis strapped to it?!

 

Nigel 

 

 

 



#6 Mr.RC-Cam

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Posted 02 January 2013 - 02:09 PM

Well, you got my interest!

 

Good! I think it will be a useful tool, especially given the very small investment.
 

 

I have an immediate use for it as a Spec-An for testing OpenLRS/HK OrangeLRS tweaked for 459MHz.

 

Frequency hopping systems can be a challenge to measure (because they hop too fast). So it will be interesting to hear if you have good results testing your LRS R/C system.

 

 

Googlin' around, I found that the RTL2832u & E4000 tuner stick is now an 'old' product, superceded by a RTL2832u & R820T tuner.
Youtube has several examples of the difference, mostly in favour of the R820T tuner.
We'll see what turns up at my doorstep.


I have the E4000. It would be interesting to know if the R820T works better for our FPV test tool application.

 

 

Failing that, it might be useful as a scanning tool at our clubs next 50MHz contest with a pair of 9 ele Yagis strapped to it?!

The R820T chip reportedly can go down to 22Mhz, so that is nice for your 50MHz application. But some SDR's won't go down to 50Mhz, so success will depend on what chip set is in your TV dongle.

An old notebook PC / SDR combo would be a cheap portable tool to scan the airwaves to see what frequencies are active at the flying field. But in the wrong hands it could just cause unnecessary confusion/worries. But the intent of this thread is to get other FPV'ers to try it out and then share any useful tips they learned. :)


- Thomas

#7 Devonian

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Posted 03 January 2013 - 11:30 AM

Mine is on it's way through eBay, but although it says it's located in the UK, that may not be true as I've had similar and it's come from Hong Kong!

 

For anyone in the UK or Europe, I found a site that seems to sell a variety of these USB sticks - wish I'd found it earlier.

 

https://www.cosycave...?id_category=56

 

If you look through the different types, they also sell adapter cables or a stick with vaious connectors.

 

I'll see what mine is and then maybe order one of the other types for testing.

 

Nigel.



#8 Mr.RC-Cam

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Posted 03 January 2013 - 12:10 PM

For anyone in the UK or Europe, I found a site that seems to sell a variety of these USB sticks - wish I'd found it earlier.

 

Thanks for the link. Prices are good.

 

 

Has anyone made a converter for the higher frequencies? I guess it would need to be very wide band!

 

Follow-up: I came across a "hobby" priced SDR based spectrum analyzer & tracking generator combo that will go up to 12GHz.

http://www.signalhound.com/

 

As you can see, the cost is about $2500 USD, which is the right direction ("real" commercial tools are priced higher than your favorite luxury sedan). So all we have to do is wait for a DiY version that meets our meager hobby budgets. I'd be thrilled to find something easy to use that could work up to 6GHz and cost under $500. It may even be out there already.

 

I'm fortunate in that I already have commercial RF spectrum analyzers in the lab. My Tektronix is rated at 18GHz and the HP is 6.5GHz. But these things are expensive and out of reach for hobbyists, even if they are purchased used on eBay. So an inexpensive no-frills hobby version that can reliably test 900MHz - 5.8GHz FPV RF gear is certainly something to wish for.


- Thomas

#9 Devonian

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Posted 03 January 2013 - 01:25 PM

I've used this free software for 2.4GHz wifi - it also does 5.8Ghz but I've never tried 5.8GHz.

Can you get 5.8GHz wifi 'dongles' ?

 

http://www.metageek....ducts/inssider/

 

Never thought to try it on my 2.4GHz FPV VTx.

No chance at present either as all my gear is in cold storage after a recent house move and the new 'man-cave' is being built (during the wettest period since records began).

 

Can any SDR software use these wifi dongles and will it 'tune' to 5.8GHz?

 

Nigel.



#10 Mr.RC-Cam

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Posted 03 January 2013 - 01:48 PM

Can any SDR software use these wifi dongles and will it 'tune' to 5.8GHz?

 

That's the $20 question. :)  As far as I know the consumer WiFi accessories are not SDR based. Instead they tend to use purpose-designed chip sets that are specific to their Wi-Fi application.

 

Since the SDR TV dongles cannot tune high enough, one possible workaround for 5.8GHz would be to use a RF down-converter with the TV SDR. That's the kind of trick being used in the video seen in post #4. But it's not very elegant and so I'd rather wait for a better DiY solution. If it's not out there now then I suspect it will be soon; So keep your eyes open for the magic stuff the ham gurus are constantly creating.


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#11 Devonian

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Posted 05 January 2013 - 04:58 AM

I ordered 2 sticks from the cozycave site and got them next day!

I ordered an E400 tuner and a 820T tuner to observe the differences.

Will try to get some time to check them out properly, but they both work fine.

 

My ebay one turned up as well and it's useless for SDR as it has the IT9135FN chipset.

 

Here is another interesting lower frequency add-on/upconverter

http://www.nooelec.c...ined-radio.html

 

I've ordered one as I sold all my radio gear when I moved house and this will be an interesting side project.

 

Haven't seen any kind of GHz converter, but I guess it will only be a matter of time.

 

Nigel.



#12 Mr.RC-Cam

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Posted 05 January 2013 - 11:13 AM

I ordered 2 sticks from the cozycave site and got them next day!

I ordered an E400 tuner and a 820T tuner to observe the differences.

Will try to get some time to check them out properly, but they both work fine.

 

That would be great if you posted a review on the two SDR's.


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#13 Devonian

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Posted 06 January 2013 - 05:10 AM

OK, tested both and although not very scientific, so far I prefer the E400 based one over the 820T one, but both will have their uses I suspect.

 

I set both up using the supplied antenna, gain set to zero and tuned to a broadcast FM radio station around 89MHz.

The E400 was fully quieting on a weakish signal (no background 'hiss').

Changed to the 820T one and it was not fully quieting with some detectable background hiss.

 

Changed to 434MHz and listened for my wireless weather staion transmissions.

Again, the E400 appeared better with what 'sounded' like a better signal.

 

Set my R/C Tx on 35MHz and the E400 could not detect the signal, but the 820T did see the signal, no problem.

 

I have no means to test any signals higher than 434MHz at the moment.

 

The 820T one has an MCX connector with adapter cables for Belling Lee and SMA.

The Belling Lee adapter cable may be an issue because I can get rid of some spikes on the Spectral display by wrapping my hand around the antenna to adapter cable joiner.

 

I may mod my E400 one to get rid of the Belling Lee connector on the PCB.

I think an SMA chassis socket may fit in there quite nicely? - that is, when I can find my stock in cold store somewhere.

 

Nigel.



#14 Mr.RC-Cam

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Posted 06 January 2013 - 09:26 AM

OK, tested both and although not very scientific, ...

Thanks for the report.

 

 

I think an SMA chassis socket may fit in there quite nicely? - that is, when I can find my stock in cold store somewhere.

 

I was going to install a edge mount style SMA too, but the ones I have were too short. What I mean is, with the SDR's plastic case installed it would have been difficult to attach the test device's plug. I could have eliminated the case or ordered a long barrel SMA, but crimping a SMA on the hacked antenna cable worked out nicely for me instead.


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#15 Mr.RC-Cam

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Posted 06 January 2013 - 07:01 PM

Nigel, it would be helpful if you ran the rtl_test program on both of your dongles and posted the results. Here's mine:

 

rtl_test.jpg

 

To run the test program you will need to use the -t option. In other words, at the command prompt it would be:

rtl_test.exe -t


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#16 Devonian

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Posted 07 January 2013 - 01:28 AM

Here's the result of both

 

Tuners_zpsaa5fa4a3.jpg

 

 

The 820T isn't recognised correctly.

 

Nigel.



#17 Mr.RC-Cam

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Posted 07 January 2013 - 08:29 AM

Thanks for posting the results. The -t option was intended to benchmark the E4000, so from your test results it seems to ignore the R820T. That is too bad.


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#18 Mr.RC-Cam

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Posted 07 January 2013 - 04:01 PM

When using my E4000 TV dongle I noticed some unusual spectrum display activity. Here's a desktop video that shows what to watch out for.

 

http://www.screencas.../t/zUVePNnk3rdq


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