Using Gqrx to Determine Cell Signal Strength

[Jericca Cleland]

I am new to using Gprx, and am running it on a Macbook Pro with Mavericks, using the NoOElec R820TSDR & DVB-T NESDR Mini.  I have a little cabin out in the country and am trying to use this device to figure out where the cell signals are strongest for setting up a wi-fi Hub.  I have the software running and set to 850MHx, which appears to be the shared radio frequency for cell carriers here (BC, Canada).  I do see a spike in the signal graph right at that frequency, so this appears to be working.

However, I don't understand how to zoom in on the frequency so that I can see more subtle changes in the signal-- right now, it appears to be exactly the same strength everywhere, which I know by looking at my cell phone to not be true.  Is there a way to attune the sensitivity to see more subtle changes?  Also, is there any kind of output value that I can see or graph (other than the visual output I get on the main screen?

I'm not really sure which menu settings to choose for best results; currently they are set to:

Filter: Normal
Mode: Narrow FM
AGC: Fast

I don't really know what those various options mean.  Any suggestions/advice/clarification would be greatly appreciated!

[Alexandru Csete]

On Sat, Nov 29, 2014 at 9:42 PM, Jericca Cleland <jeri...@gmail.com> wrote:
> I am new to using Gprx, and am running it on a Macbook Pro with Mavericks,
> using the NoOElec R820TSDR & DVB-T NESDR Mini. I have a little cabin out in
> the country and am trying to use this device to figure out where the cell
> signals are strongest for setting up a wi-fi Hub. I have the software
> running and set to 850MHx, which appears to be the shared radio frequency
> for cell carriers here (BC, Canada). I do see a spike in the signal graph
> right at that frequency, so this appears to be working.

Be careful, narrow spikes are often spurs (artifacts generated inside
the dongle or interference from some external electronic devices)

> However, I don't understand how to zoom in on the frequency so that I can
> see more subtle changes in the signal-- right now, it appears to be exactly
> the same strength everywhere, which I know by looking at my cell phone to
> not be true.

Normally, you can zoom in by using the mouse scroll wheel on the
frequency bar, but as I recall that functionality is broken on OS X
(or may require an external mouse with wcroll wheel).

Is there a way to attune the sensitivity to see more subtle
> changes? Also, is there any kind of output value that I can see or graph
> (other than the visual output I get on the main screen?
>
> I'm not really sure which menu settings to choose for best results;
> currently they are set to:
>
> Filter: Normal
> Mode: Narrow FM
> AGC: Fast
>
> I don't really know what those various options mean. Any
> suggestions/advice/clarification would be greatly appreciated!

These settings only matter if you want to demodulate radio
transmissions. If you only want to observe the signal on the spectrum
plot you can set the mode to "Demod Off". That wil lalso save you some
CPU. Try to play with the gain seetings on the "Inpout Device" tab.

Alex

[grege...@gmail.com]

Using an SDR will show you all signals in a band, but you won't be able to tell which ones are from your cellphone service provider.  I just came across a free Android app called Network Signal Info, available on the Google Play store for Android, from kaibits-software.com.  If you are using an Android smartphone or have access to one that uses your network, this app gives a detailed signal strength display and also tower identification.  There is also a paid version with more features, but you probably won't need that.