Re: [Hackrf-dev] Narrowband fm - what is the secret?
On 09/15/2016 08:03 AM, Kevin Reid wrote: > On Sep 14, 2016, at 19:55, Cinaed Simson 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 > HackRF-dev@greatscottgadgets.com > https://pairlist9.pair.net/mailman/listinfo/hackrf-dev > ___ HackRF-dev mailing list HackRF-dev@greatscottgadgets.com https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
Re: [Hackrf-dev] Narrowband fm - what is the secret?
I did make some progress on this, as follows: - temporarily attached rubber-ducky antenna from handheld, onto the hackrf One; got a very faint signal - zoomed in on frequency display and determined that frequency correction of 10 ppm centered the bandwidth on the target frequency Once I found the signal, I tried again with & without the RF amp, I could see all the spectrum move up, but not much difference to the SNR. Per Kevin's suggestion, I will try a different antenna and a better (higher) location in the attic. This is getting a bit off topic, but I will need an omni-directional antenna, with some gain in the 2m band - perhaps a discone? Thanks, Jake From: HackRF-dev on behalf of Kevin Reid Sent: September 15, 2016 9:03 AM To: hackrf-dev@greatscottgadgets.com Subject: Re: [Hackrf-dev] Narrowband fm - what is the secret? * 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: 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. <https://pairlist9.pair.net/mailman/listinfo/hackrf-dev> ___ HackRF-dev mailing list HackRF-dev@greatscottgadgets.com https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
Re: [Hackrf-dev] Narrowband fm - what is the secret?
On Sep 14, 2016, at 19:55, Cinaed Simson 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. 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. > 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: 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 HackRF-dev@greatscottgadgets.com https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
Re: [Hackrf-dev] Narrowband fm - what is the secret?
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. See if SDR has a APRS decoder plugin. Note, gqrx has a APRS decoder. -- Cinaed 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). > > My first guess is that I have missed some RF setting, but I've been > through the menus and can't find anything. > > Once again - any advice is welcome. > > > Jake > > > > ___ > HackRF-dev mailing list > HackRF-dev@greatscottgadgets.com > https://pairlist9.pair.net/mailman/listinfo/hackrf-dev > ___ HackRF-dev mailing list HackRF-dev@greatscottgadgets.com https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
