SDR# - can't receive on NFM only

eorange · Jan 26, 2015

I just installed the latest version of SDR# and the ZADIG drivers on a new Windows 8.1 PC. For some reason I cannot open the squelch in NFM, and also couldn't hear the local NOAA tower. It doesn't matter if I have the squelch checkbox set or not. NFM is basically silent.

Every other mode produces squelch noise and receives. In fact, I can sort of hear the NOAA tower through WFM, as well as local FM radio stations.

What am I missing here?

Voyager · Jan 26, 2015

Did you reset the gain in the configuration?

How low did you set the squelch?

eorange · Jan 26, 2015

Was a dumb mistake I didn't catch...my filter bandwidth was way too low (like by 20000). Working excellent now.

Voyager · Jan 26, 2015

20,000 too low? As NFM is between 4,000 and 16,000, how is that possible?

eorange · Jan 26, 2015

Well, "1000" was the number in the field, for however that happened. At 16000, it's still a little scratchy. 22000, for better or worse, results in crystal clear NOAA NFM audio.

My RTLSDR doesn't have RTL AGC or Tuner AGC checked, and RF Gain is 22.9 dB, fyi.

It's entirely possible I'm not set up optimally.

WQPW689 · Jan 28, 2015

SDR#

I have Tuner AGC checked on in the Configuration Box (Offset Tuning also, forget why!). This gives me 8000 bandwidth filter and it sounds great on NOAA 162.550. When I check Use AGC on the front panel the volume rises perceptibly, and shows a default threshold of -50dB.

Squelch to taste.

Good luck.

Voyager · Jan 28, 2015

eorange said:
Well, "1000" was the number in the field, for however that happened. At 16000, it's still a little scratchy. 22000, for better or worse, results in crystal clear NOAA NFM audio.

That sure does sound like it's not properly calibrated. Check your calibration against the NOAA transmitter. The carrier should be right on the red line. If it's not, adjust the ppm until it is and 16000 should sound perfect.

Also note this value for future reference.

eorange · Jan 29, 2015

That makes sense - an extra-wide filter to accomodate an off-frequency signal. Will calibrate tonight.

On my former computer...I had to calibrate the RTLSDR when using the 100 MHz downconverter when listening to 75M. Now that I think of it, I never considered calibration for VHF and UHF signals, maybe because I had already done it. The off signal was way more noticeable when listening to LSB signals.

eorange · Jan 29, 2015

Voyager said:
adjust the ppm until it is and 16000 should sound perfect.

Thanks, that was it. Perfectly calibrated now; signal is crystal clear with a filter range anywhere from 10000 to 16000.

mikepdx · Jan 29, 2015

eorange said:
... crystal clear NOAA NFM audio.

162.xxx NOAA broadcasts are NOT narrow band FM.
Am I missing something?

BM82557 · Jan 29, 2015

mikepdx said:
162.xxx NOAA broadcasts are NOT narrow band FM.
Am I missing something?

NOAA says -

Voyager · Jan 30, 2015

mikepdx said:
162.xxx NOAA broadcasts are NOT narrow band FM.
Am I missing something?

Yes - you're missing the fact that NBFM is what they have always been - just like all other transmitters from the 60s to around the 90s, and most until a couple years ago with the FCC's SNFM mandate for Land Mobile between 136 and 470 MHz.

You're also missing the fact that SDR# does not have a NBFM/SNFM distinction, so anything that is not WFM (broadcast) is NFM (FM, NBFM, and SNFM).

As he said, the bandwidth of 16,000 (which is NBFM) is working fine.

SDR# - can't receive on NFM only

eorange

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