Page 1 of 1

need help... nothing but noise

Posted: Sat Nov 29, 2014 10:26 pm
by greenpin
I've installed rtl-sdr, gqrx, gnuradio, and all the dependencies (on Linux Mint 17), and using a new NooElec NESDR Mini 2 dongle. I've got the antenna connected and fully extended. No matter what frequency I tune to in gqrx, I'm just receiving noise (blue waterfall mostly) -- even for local FM radio stations.

Am I doing something wrong?

rtl_test -t shows:

Code: Select all

Found 1 device(s):
  0:  Generic, RTL2832U, SN: 77771111153705700

Using device 0: Generic RTL2832U
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6 
Sampling at 2048000 S/s.
No E4000 tuner found, aborting.


Re: need help... nothing but noise

Posted: Mon Dec 01, 2014 1:50 am
by rtlsdrblog
Have you been adjusting the RF gain? I believe that control is under the Input Controls tab in GQRX.

Re: need help... nothing but noise

Posted: Mon Dec 01, 2014 2:32 am
by greenpin
I have played with the LNA Gain option, as well as the Audio Gain option. If I increase the LNA Gain to near max (49.6 dB), and set the Audio Gain to somewhere between 1.6 and 12 dB, then I am able to faintly hear some of the stronger sources in the area. I live in the Dallas metro -- would think there would be a lot of strong sources, but only finding a few. I have discovered that I can receive some ADSB (using dump1090), so that's something.

I am beginning to think the problem is really with the small telescoping antenna that came with the dongle. I've ordered an MCX to F and SMX pigtails so I can try other antennas. Figured I would build one of those DIY coaxial collinear antennas for 1090 MHz. I will try moving the antenna outdoors, too (my house has a radiant barrier roof and rmax rigid side wall insulation (lots of aluminium foil).

I'm a total noob to RF... when should one suspect the dongle is defective?

Re: need help... nothing but noise

Posted: Mon Dec 01, 2014 3:09 am
by rtlsdrblog
I can see weak FM stations on your waterfall image. But it just sounds like you just have weak broadcast FM reception at your location. If your inside surrounded by walls and buildings you can expect poor reception, especially with a small antenna like the one provided which is not tuned to broadcast FM frequencies. Try place the magnetic mount on a metallic object like a coffee tin lid or cookie can lid and take it outdoors and put it up as high as you can.

For ADS-B use the telescopic antenna collapsed, its tuned better for 1090 MHz that way.

It's hard to tell if one dongle is defective without a reference radio connected to the same antenna if you have no experience. But generally if you've put your antenna outside up high and unobstructed and adjusted the LNA gain and you still can't get broadcast FM, then its probably faulty.

Re: need help... nothing but noise

Posted: Mon Dec 01, 2014 3:14 am
by greenpin
rtlsdrblog, thanks for your responses. I will reply once I'm able to test with a better antenna and outdoors.