On 09/15/2016 08:03 AM, Kevin Reid wrote:
> On Sep 14, 2016, at 19:55, Cinaed Simson <cinaed.sim...@gmail.com> 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# v184.108.40.2063 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
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
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
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