[Hackrf-dev] Static/warbling non reception issue

[Dominic Spill]

On 30 April 2016 at 00:32, David Goldstein
<davidmarkusgoldstein at gmail.com> wrote:
> Hi, here's a screenshot of the settings that I can change, plus the spectrum analysis shot.  The audio I get is heavily distorted on the strong local FM stations.

The station at 101.5MHz looks like an excellent signal.

> So, I have no idea what's wrong, except that it could be the sound driver or on-board sound.

Are you demodulating the signal at the centre frequency?  Or at an
offset?  The spike in the middle is the DC offset, so if you're
demodulating there you're going to see bad data.  It's explained in
more detail here:
https://github.com/mossmann/hackrf/wiki/FAQ#what-is-this-big-spike-in-the-center-of-my-received-spectrum

Thanks,
  Dominic

> -----Original Message-----
> From: Dominic Spill [mailto:dominicgs at gmail.com]
> Sent: Friday, April 29, 2016 5:40 PM
> To: davidmarkusgoldstein at gmail.com
> Cc: hackrf-dev
> Subject: Re: [Hackrf-dev] Static/warbling non reception issue
>
> On 29 April 2016 at 17:31, davidmarkusgoldstein at gmail.com <davidmarkusgoldstein at gmail.com> wrote:
>> Hi, how can I test the hackrf to see if it's damaged?  I have sound
>> card issues, it seems, on my i7-2600 win7 64 bit system, so I tried it
>> on a Vista laptop and experienced the same: static and choppiness and
>> some distorted voice on local fm.  So perhaps the radio is damaged.
>
> This doesn't necessarily mean that the radio is damaged, although we can help to test whether it is, but it may be something not quite right in your settings.  Telling us which settings you are using for sample rate, gain, filter, etc would really help us to diagnose the problem.
>
> Thanks,
>   Dominic
>
>> -------- Original message --------
>> From: Dominic Spill
>> Date:04/28/2016 7:31 PM (GMT-05:00)
>> To: davidmarkusgoldstein at gmail.com
>> Cc: hackrf-dev
>> Subject: Re: [Hackrf-dev] Static/warbling non reception issue
>>
>> On 28 April 2016 at 20:28, davidmarkusgoldstein at gmail.com
>> <davidmarkusgoldstein at gmail.com> wrote:
>>>
>>> Hi, this might not be a tech support list but I don't know what to do
>>
>> Hi David,
>>
>> We're happy to provide tech support through this mailing list; I'm
>> sure we'll be able to help you.
>>
>>> ...everything seems set up properly but I get static and broken up
>>> voice broadcast on local fm.  I think it's the alc889 Realtek sound
>>> card doing this...I had this issue with a winradio g 315 because I'm
>>> running win 7 64bit.
>>
>> Are you using SDR# on your Win7 install?  Could you give us some
>> examples of the settings you are using?  If it's easier, you can
>> attach a screenshot of the setting panel in SDR# (or whichever tool
>> you're using).  You could also attach a screenshot of the tool so that
>> we can see how strong the signal is compared to the background noise.
>>
>>>  They tweaked a driver for me and I got the winradio running but I
>>> don't know what to do now with the hackrf I have, if it is the sound
>>> card at all.  Any tips?
>>
>> One option would be to try not using realtime processing.  Capture ~20
>> seconds FM station to a file, then demodulate it from the file
>> afterwards.  Finally, you should be able to play back the file as
>> audio.  If it's a problem with the quality of the signal being
>> received, the output will still be choppy, but if the output is smooth
>> we can look at where else things may be going wrong.
>>
>> It certainly looks like you have enough CPU power and RAM to support
>> the task that you're trying to do, so we'll have to narrow down where
>> the problem could be.
>>
>> Thanks,
>>   Dominic