RF Analyzer, SDRTouch, and RTL-SDR

[caspar347]

I just happened across a couple of apps on the Play store that look like they could potentially be used as low-fi basic barebones spectrum analyzers for looking at spectrum utilization. Both apps advertise the ability to scan the full range possible with an RTL-SDR stick (nicer ones with an Elonics E4000 tuner can apparently pick up 55mhz through 2200mhz with a small gap somewhere around 1200mhz) but as far as I can tell (without an actual stick and USB-C OTG cable to test with) you can't view more than 120khz at a time with SDRTouch. However (again without actual hardware to test with) it looks like you can set custom scan sizes with RF Analyzer as long as you aren't trying to demodulate.

 

SDRTouch:

https://play.google.com/store/apps/details?id=marto.androsdr2

 

RF Analyzer:

https://play.google.com/store/apps/details?id=com.mantz_it.rfanalyzer

 

I'm totally unfamiliar with a lot of the terminology involved, but it looks like RF Analyzer should in theory let me look at frequency use/carrier size if I bought a dongle? Anyone have any experience with any of this stuff? The involved hardware isn't too expensive ($35 for a "guaranteed genuine Elonics E4000+RTL2832U"; apparently there are a lot of shady generic dongles out there, and $1 for a powered OTG cable) so I'm considering going ahead and picking this stuff up and trying it.

[kineticman]

I have a little USB SDR that I picked up for $35. I run it for a ADS-B receiver (airplane traffic). Never tried it for what you are thinking but it should work just fine.

 

The most important thing on those is the proper antenna for the frequency you are looking for.

[caspar347]

I have a little USB SDR that I picked up for $35. I run it for a ADS-B receiver (airplane traffic). Never tried it for what you are thinking but it should work just fine.

 

The most important thing on those is the proper antenna for the frequency you are looking for.

Awesome! I just ordered the SDR that I linked.

[caspar347]

The stick is here! And it kinda works. As far as I can tell, it gets too hot anywhere above FM frequencies to be useful (i.e. it can't see anything over what I assume is internally generated noise) while mobile. The weird part is the chips themselves don't get hot. It's the antenna connector. I opened it up to verify.

 

But in the freezer and connected to a laptop with a USB extension cable, I can see this:

 

 

The way the waves keep bumping I can see three distinct sections which must be CDMA carriers on channels 325, 350, and 375. I'm using a program I found through 10 seconds of googling and I'm open to suggestions on better programs. Can anyone think of a way to get the stick close enough to a tower to see active carriers on that tower without bringing a mini-fridge?

[caspar347]

Tuning to the UL frequencies gives three distinct spikes.

 

[caspar347]

And a wider sweep shows what I expected if I'm interpreting this right.

 

 

Nearby carriers at 325 and 375 plus a distant one at 350. Nothing in the 200s as I believe that range is usually reserved for high capacity setups in my market.

[kineticman]

The stick is here!

 

Can anyone think of a way to get the stick close enough to a tower to see active carriers on that tower without bringing a mini-fridge?

Never heard of receiver getting hot? You could stick in a can of oil.

 

http://rtlsdr4everyone.blogspot.com/p/cooling.html?m=1

[caspar347]

Never heard of receiver getting hot? You could stick in a can of oil.

 

http://rtlsdr4everyone.blogspot.com/p/cooling.html?m=1

I'm totally new to this whole thing, so I'll probably have some more weird questions. 

The stick actually works temperamentally at the frequencies I need without cooling but it definitely works consistently when cooled. I'll have to try that out.

 

I'll have more time to play with it tomorrow but it looks like I was lucky enough to get a tuner with AWS inside of its operational range!

[caspar347]

Well I was only kinda lucky. I haven't successfully gotten it to tune above 2152ish. So I can see all of AWS-1 minus part of the F block. But the part I can see is enough to tell me T-Mobile's running a 15x15 LTE carrier in it. So it doesn't matter a whole lot.

 

I also found some better software. http://eartoearoak.com/software/rtlsdr-scanner

It took a good half hour of fiddling with the dependencies (the whole package works better on 32-bit systems for whatever reason  ) but I eventually got it working.

 

I can save outputs like this:

 

 

Really cool stuff.

[kineticman]

Not bad for $35 huh

[caspar347]

Not bad for $35 huh

Beats a $1000 pro analyzer for sure. I'm surprised nobody's tried to do this before.

[WiWavelength]

Beats a $1000 pro analyzer for sure. I'm surprised nobody's tried to do this before.

 

On price, yes.  But on capabilities, a resounding no, says my relatively inexpensive $1500 pro spectrum analyzer.

 

AJ

[caspar347]

On price, yes.  But on capabilities, a resounding no, says my relatively inexpensive $1500 pro spectrum analyzer.

 

AJ

Oh for sure. All I can really do is see whether a given block is in use and maybe guess what's in the block based on the guard band sizes. Comparing this to a real analyzer on capability is like comparing a bike to a car. Totally different functional leagues.

 

But that's pretty much all I need it for. I don't need to actually do a whole lot of proper "analysis". 

 

I'm just mildly surprised nobody else on the forum has ever stumbled upon this, especially back when we cared more about which/how many live CDMA carriers were on a site. Because this is basically the only cheap way to do that. Unless of course you already have a real analyzer or live near someone who does.

[belusnecropolis]

Well, WiMAX is still there. 

[belusnecropolis]

Oh for sure. All I can really do is see whether a given block is in use and maybe guess what's in the block based on the guard band sizes. Comparing this to a real analyzer on capability is like comparing a bike to a car. Totally different functional leagues.

 

But that's pretty much all I need it for. I don't need to actually do a whole lot of proper "analysis". 

 

I'm just mildly surprised nobody else on the forum has ever stumbled upon this, especially back when we cared more about which/how many live CDMA carriers were on a site. Because this is basically the only cheap way to do that. Unless of course you already have a real analyzer or live near someone who does.

Good work getting that together, thanks for keeping updates on the results.

 

The price is phenomenal, and plugs into the phone, I never could find a phone module, also great find.The best scanner one can have is the one they have on themselves at the time. Please keep us updated. I just scooped up an explorer a couple months ago.

[caspar347]

 

Well, WiMAX is still there. 

From Clear gear? Shouldn't that all have been disabled a long time ago?

 

And that's another thing, my stick maxes out at 2150 (and I'm pretty sure the tuner was designed for sub-1ghz OTA TV so certainly no optimization for the frequencies I'm after) whereas the pro analyzers that cover PCS usually at least cover up to 2.4 ISM. I'm actually a little bummed out that I can't see AWS-3 since the stick I got is advertised as working up to 2.2 Ghz. Chip fabrication is hard I guess. How high does yours go?

[belusnecropolis]

From Clear gear? Shouldn't that all have been disabled a long time ago?

 

And that's another thing, my stick maxes out at 2150 (and I'm pretty sure the tuner was designed for sub-1ghz OTA TV so certainly no optimization for the frequencies I'm after) whereas the pro analyzers that cover PCS usually at least cover up to 2.4 ISM. I'm actually a little bummed out that I can't see AWS-3 since the stick I got is advertised as working up to 2.2 Ghz. Chip fabrication is hard I guess. How high does yours go?

Yeah we have the protection sites still. I check every now and then if they are still on, this replaced the Photon's last jerb.

 

High end is 2700, which is precisely why I grabbed one. Works nicely so far, and I have not tore it down yet to see what I can't break; in the software or the module. I suppose it (can)logs and I intend to explore this when I am able as well.

 

Cool addition to the power block when we travel so far. I let it operate for about 45 minutes or so on a good stretch of 501 and it held up great. Had it tethered on the laptop looking for activity on our last trip. I am working on a side project to get this thing some better signal when our season slows down a notch or 11. 

 

I will definitely grab a model like AJ's if I manage to score moAr in depth RF training, or some work I suppose.

 

In the meantime this has helped my search by identifying the second carrier on our 41 cow and a couple other spots around the house with WiFi. Thank you for starting this thread. 

[WiWavelength]

Oh for sure. All I can really do is see whether a given block is in use and maybe guess what's in the block based on the guard band sizes. Comparing this to a real analyzer on capability is like comparing a bike to a car. Totally different functional leagues.

 

But that's pretty much all I need it for. I don't need to actually do a whole lot of proper "analysis". 

 

The issues with rigging a spectrum analyzer out of a digital TV tuner stick are threefold:  RF electronics, antenna, and software.  The weaknesses seem to be in the latter two.

 

The antenna is omnidirectional.  That proves problematic -- unless you can get really close proximity to the sector under measurement.  Otherwise, signal from other sectors is polluting your measurement.

 

Then, the RF analysis software is amateur freeware.  For basic frequency domain graphs, it looks decent.  But other analysis as well as fine adjustments may be outside of its scope.

 

AJ

[belusnecropolis]

In my experience recently I found quite a few affordable, yet larger directional mounted antennae for my latest project while digging around the internets. Some with, some without a mount, they have lots of models that cover up to BRS areas. Without a pre-amp you may expect a few decibels in your favor over the omni of course, yet it may take a little bit longer to get the signal you want. I started with a couple devices in areas that were terrible, say -115> on the aircard and N5s. Got tall and mounted one temporarily after some searching. It was fun for sure. Try out one to see if you can maybe get a bit more specific to a beam. That may depend on your software of course but imagine that should be available.

Dependent upon your rf conditions, size of your experiment area, localization, compulsion to see if a better signal is over here, and naturally cable length. 

The model I use has two omni's that have their uses for sure. A nice low band one, and a decent wider setup. It is great so far for driving and sniffing the air when we go on long drives. When navigating, it is handy to have a good software interface when using this as a peripheral. Works great to read while being aware of new surroundings. Will be golden if I get up to date on capabilities, which I assume will require some moAr forums. AJ nailed it per what he does. Get to know those warez I suppose. Hope this helps or does not distract too much.