On 09/15/2016 08:03 AM, Kevin Reid wrote: > On Sep 14, 2016, at 19:55, Cinaed Simson <[email protected]> wrote: >> Hi - neither APRS or AFSK are FM modulated. >> >> AFSK is digital and uses 2 frequencies - FM is analog and uses a wide >> range of frequencies. >> >> APRS is packet based and you need to decode it - which is what your >> handset is doing. > > This is not correct. > > “A”FSK (as opposed to FSK) refers to FSK whose two frequencies are in the > audio range, and in this context specifically placed into the audio > input/output of an FM transmitter/receiver.
2 audio frequencies are 2 frequencies. > > APRS consists of digital data on a specific AFSK modulation. Gavin Jacobs is > talking about _listening_ for that audible AFSK signal -- it has an easily > recognizable sound and should not resemble silence with a narrow-band FM > demodulator. From everything I read, they are doing everything right. You can demod the APRS signal as AM, FM, LSB, USB, CW-L or CW-U - they will all make sounds when the APRS signal is present. > >> On 09/14/2016 09:03 AM, Gavin Jacobs wrote: >>> Yesterday (thanks to help here on this mail list) I got my hackrf One >>> working as an FM receiver. I have SDR# v1.0.0.1483 running on Windows >>> 10. So, today I want to move on to narrowband fm. I picked APRS channel >>> because there is steady traffic. I tuned SDR# to 144.39 MHz, NFM, >>> bandwidth 8k, LNA gain 32, VGA gain 24, amp off (also tried on), squelch >>> off, antenna adjusted to 52 cm. >>> >>> If I key my handheld, I see a big spike on the frequency; and if I zoom >>> in, it appears centered on 144.39. Meanwhile, on my handheld, I can >>> hear the AFSK tones, so I know there are signals coming in, but the >>> hackrf/SDR# doesn't change (neither frequency nor audio). > > If I read your description correctly, then you're saying that > * you can hear APRS packets on your handheld, and > * you can see a signal from your handheld on your HackRF One, but > * you cannot see or hear APRS packets using the HackRF One. > > This suggests that the signal is sufficiently weak that it is below the > HackRF One's receive noise floor, but not for your handheld. Then, some > possibilities: But he indicated there was a "big spike" in the frequency - by big I presume it was well above the noise floor. In fact, it was probably well above the HackRF's DC offset. It's unlikely it's an antenna problem - which doesn't mean it can't be improved. Also, is turning off the squelch equivalent to setting it to 0 dB? Try a little squelch and see what happens. If that doesn't work, try the same FM station as before again and see if you can hear anything. And as a last resort, given it's a Windows 10 machine, try rebooting it. > > 1. Your HackRF One does not have a good enough antenna (for the frequency) > attached to it. > > 1a. Your handheld is more sensitive/more selective/... and so you will need a > _better_ antenna to get the same performance. > > 2. Your gain settings are too low (signals below inherent noise) _or_ too > high (overload creates more noise). Find some other signal in the band (e.g. > a repeater) and adjust for maximum SNR (vertical distance between the signal > peak and the noise floor). > > 3. Your HackRF One is damaged. Damage can be caused by overly-strong nearby > signals such as transmitting with your handheld, but IIRC the most likely > failure is the 14dB amplifier and that can be bypassed, so that's not the > problem here given that you have the amp off. But as a general principle, > don't do that unless you have an attenuator or dummy load on one or the other > device. > > > _______________________________________________ > HackRF-dev mailing list > [email protected] > https://pairlist9.pair.net/mailman/listinfo/hackrf-dev > _______________________________________________ HackRF-dev mailing list [email protected] https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
