[hfsig] Sidebands on Raspberry Pi WSPR carrier

Zoltan Doczi zoltan.doczi at gmail.com
Sun Sep 4 04:06:05 CDT 2016


Hi Ron,

Just to clarify: you seen the +/- 120 Hz spurious in the audio base band,
not in the RF spectrum around 14 MHz if I'm right? The RF spectrum has some
modulation side bands +/- 1.1kHz (as every transmitter has) but it's almost
60dBc so pretty clean.

Can you share us a screenshot?

Also if you looking at your own signal take care to use decent attenuation
as a strong signal may overload your receiver and cause distortion which
can mislead the measurement.

73,
HA7DCD
Zoltan

On Sun, Sep 4, 2016 at 9:17 AM, Orrin Winton <orrin.winton at gmail.com> wrote:

> I may be experiencing that too. I say *may* because i haven't looked at it
> with another radio + waterfall like fldigi.
>
> But i *hear* with my ear a lot of grunge on my transmitted signal,
> listening with another radio 20 feet away.
>
> If i disconnect the antenna from the 2nd radio, i hear just the pure tone.
> Which is what you'd expect if the grunge was quite a few dB down from the
> main signal.
>
> I may try some other 5V power source and see if there is any change.
>
> Orrin WN1Z in CN90
>
> On Sep 4, 2016 00:05, "Ron Ott" <ronott at sbcglobal.net> wrote:
>
>> This is my first post to the group, my apology if I'm not following the
>> correct protocol.
>>
>> I just got a Raspberry Pi 3 working on 20m WSPR using the TAPR kit. I
>> quickly discovered that there are sidebands 120Hz above and below the
>> carrier frequency and these sidebands are modulated like the carrier and
>> are only 15dB or so below it in amplitude.
>>
>> In the last few days I read some chatter about others seeing such
>> sidebands on received WSPR signals, but there was no mention of a Raspberry
>> Pi (normally the listener wouldn't know what the sender is using).
>>
>> I'd be surprised if no one else has discovered this issue, which is
>> serious since the sidebands are pretty strong.  I suspected modulation by
>> the main USB power source, but tried other supplies including a well
>> regulated HP with no change.
>>
>> What's the solution?
>>
>> Thanks, Ron / W6XY
>>
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>>
>>
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