RTL SDR AS AN ANALYSER?

sinus trouble · Post by **sinus trouble** » Fri Oct 09, 2015 11:35 pm

Greetings Neckies!!

Ive had one of these dongle things for a while now and it seems to work fine?
Although id love to splash out on a spectrum analyser for my toolkit, they are still very pricey
in the 21st century!
il upload some pics to show the signal from one of my rigs!
if youve used one of these? or have any comments? please share! however harsh lol!

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sinus trouble · Post by **sinus trouble** » Fri Oct 09, 2015 11:49 pm

Just to add, the dongle has a basic antenna included which is very small? likely to be tuned for UHF reception!
Maybe i can knock up a sampler to plug direct into the dongle? risky but worth a go lol

Post by **sde-1104** » Sat Oct 10, 2015 8:33 am

I have one. The standard aerial is rubbish but they can be replaced with better ones. I have used one as an analyser when doing some testing but I can't be certain on how accurate they are. Hope this helps.

yellowbeard · Post by **yellowbeard** » Sat Oct 10, 2015 10:17 pm

I got a couple of those, €7 Euro including post from Hong Kong it'd be rude not to. sde-1104 is right about the aerial and the accuracy, but what I would like to know is what is the software you are using in the pictures? I got HDSDR for it, the waterfall display is good lookin' AND trippy.

sinus trouble · Post by **sinus trouble** » Sun Oct 11, 2015 12:14 am

Lol id have to agree! mine was given to me by a contact in radio! and I believe it cost around 10 quid? and through experience? something that cheap has a catch? lol I pickup the usual London stations, band 1 and sometimes local microwave links!
As shown my pro rigs seem pretty clean with the odd spike close to the carrier when the gain of the dongle is set high? I also tested a pantek copy which had spuri and spikes up and down the band lol
The software im using is SDR Sharp www.rtl-sdr.com they have a tutorial on installing and many of the other millions of apps for this device! I cant remember exactly the installation process? but I had to use a patch called "zadig" to get it running/ but its all explained in the tutorial!

the trippy waterfall is also on sdrsharp I just chose to display the IF and audio response instead lol

pjeva · Post by **pjeva** » Sun Oct 11, 2015 9:35 am

For basic testing this is ok device. When you want to measure more precise, turn off its gain completely (both device and software gain). Antenna is not good for any band. You could cut it off and solder some rf connector and use normal antenna or connect it to directional coupler.
This is cheap enough to have it anyways. Also, for testing purposes, you can build your own spectrum analyser which can measure up to 500MHz fairly easy with AD8307, and use cheap analog oscilloscope with like (10MHz bandwidth. Same setup can be used for network analyser...

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shuffy · Post by **shuffy** » Sun Oct 11, 2015 10:09 am

sinus trouble wrote:Although id love to splash out on a spectrum analyser for my toolkit, they are still very pricey

http://radionecks.co.uk/viewtopic.php?f ... 4373#p4367

shuffy · Post by **shuffy** » Sun Oct 11, 2015 10:10 am

sinus trouble wrote:Maybe i can knock up a sampler to plug direct into the dongle? risky but worth a go lol

What sort of a sampler?

sinus trouble · Post by **sinus trouble** » Sun Oct 11, 2015 9:26 pm

Thankyou SDE, Pjeva and shuffy! I guess the conclusion is that the SDR is a nice novelty item but no substitute for a proper analyser!
The sampler would probably be just a couple of resistors and a cap to nick a little signal off the RF feed from the TX to go direct into the dongle? lol but pointless now as all your comments have summed up!

Also thanks again mr Pjeva for AD8307 info! I happen to have a 25mhz spectrum analyser, so definately worth looking into!

thewisepranker · Post by **thewisepranker** » Mon Oct 12, 2015 9:15 am

sinus trouble wrote: I happen to have a 25mhz spectrum analyser

Do you mean oscilloscope?

sinus trouble · Post by **sinus trouble** » Mon Oct 12, 2015 9:20 pm

Lol yes mr pranker, oscilloscope is what i ment! forgive my utterr incompetence!
im not exactly sure how the AD8307 works either lol i need to have a good read of the datasheet, try get my head round it!

pjeva · Post by **pjeva** » Tue Oct 13, 2015 1:00 am

I will do some basic drawing tomorow so you can get an idea Mr. Sinus

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Shedbuilt · Post by **Shedbuilt** » Mon Oct 19, 2015 2:43 pm

sinus trouble wrote:Lol yes mr pranker, oscilloscope is what i ment! forgive my utterr incompetence!
im not exactly sure how the AD8307 works either lol i need to have a good read of the datasheet, try get my head round it!

AD8307 is a Logarithmic Amplifier chip, which can work up to about 500MHz.
The link which follows, shows an idea for a 2.4G spectrum analyser adapter (to work with X and Y inputs of a 'scope). It's narrow band - only sweeps from 2.4G to 2.5G, and uses the AD8307 as a Log Amp, for a 500MHz I.F. If you substituted the VCO, for one which can sweep 500MHz to 1GHz, and changed the front end accordingly (Broadband amplifier, followed by a 500MHz Low Pass filter in place of the 2.4G bandpass filter etc), you'd have a spectrum analyser which could sweep from 0 - 500MHz. By using a single I.F at 500MHz, however, the problem would be bandwidth. A bandpass filter at 500MHz, will be much too wideband. The principle of operation is effectively a superhet receiver, so it has the same set of compromises (high I.F makes image rejection easier, but gives low selectivity; low I.F makes it easier to get the selectivity, but makes image rejection difficult). Like a superhet receiver, to achieve narrow bandwidth, I think it would need multiple stages of I.F - where the final I.F would need to be low; to achieve the response shape you need to see the close-in stuff. http://www.qsl.net/va3iul/2.4GHz_Spectr ... alyzer.htm

alfaeire · Post by **alfaeire** » Mon Oct 19, 2015 3:42 pm

Ive been looking into these as well, theres a second version with a better chip.. loads of mods can be done..

check out https://www.facebook.com/groups/rtlsdrdongle/?fref=nf

sinus trouble · Post by **sinus trouble** » Mon Oct 19, 2015 9:39 pm

Many thanks Mr Shed for the schematic and your knowledge!

Im gonna try source some for experimenting, hopefully they aint too expensive lol

Shedbuilt · Post by **Shedbuilt** » Wed Oct 21, 2015 5:30 pm

If you're just looking for something to experiment with, and see the principles, then this is a simple way to start, but set your expectations accordingly. I "think", if you go with a single IF at 500MHz, even with a fairly sharp bandpass filter, you'll be looking at passband in the tens of MHz, so, for example, if you view a signal on 98MHz, it will appear to spread across most of Band II. With a really sharp filter, you could probably get the bandwidth down to a few MHz. If you want something with a useful purpose at the end of it, I think you really would need to go with a multiple conversion approach. Going for a 10.7MHz final I.F (for the sake of a standard frequency, with available filters etc), for example, with crystal I.F filters, could get that down to a few KHz, but with a bit more complexity. You'd probably want an interim I.F as well, and you could take it further. There are a number of home brew analyser projects on the internet. More complicated than the one I pasted before, but broken down into manageable modules. I'll paste some more links if you like.

sinus trouble · Post by **sinus trouble** » Wed Oct 21, 2015 10:39 pm

Mr Shed, your knowledge is priceless! it seems that by what you are saying? to get a working accurate design, id need a top quality, calibrated spectrum analyser in the first place to evaluate its integrity? lol maybe i should stop being a tight ass and invest in a decent analyser! there is some excellent PC based units for around a 1000 quid!

thewisepranker · Post by **thewisepranker** » Thu Oct 22, 2015 9:07 am

sinus trouble wrote:there is some excellent PC based units for around a 1000 quid!

New or used? Got a link?

teckniqs · Post by **teckniqs** » Thu Oct 22, 2015 10:11 am

I think I saw those PC based devices for around £100-200 the last time someone posted up a link on one of the previous forums.....

pjeva · Post by **pjeva** » Thu Oct 22, 2015 3:28 pm

Check this link:

http://www.qsl.net/va3iul/Homebrew_RF_C ... _Ideas.htm

Some not so easy to build projects, but you can get idea how spectrum analyser and other rf gear work.