[Skimmertalk] Attn: Red Pitaya 16-bit users decoding FT8

[Björn Ekelund]

I have seen this several times also with "normal" receivers so I believe it
is generated at the transmit side.
But never this strong. The cases I have seen the "ghosts" have been 15-20dB
below the "main" signal.

If the signal is inadvertently modulated by 50Hz hum leaking into the audio
path, it would give exactly this effect.

Björn SM7IUN

Den ons 31 juli 2019 kl 14:21 skrev John Ackermann. N8UR <jra at febo.com>:

> I've seen that a few times with WSJT-X 2.1.0 using an IC-7300 as the
> radio, so it may not be related to the RPi.
> On Jul 30, 2019, at 5:33 PM, N4ZR <n4zr at comcast.net> wrote:
>>
>> I'm noticing a strange phenomenon using WSJT-X to decode FT8 messages.
>> Fairly often, I see multiple spots of the same station in the same
>> transmission period.  Invariably, the highest-frequency spot is the loudest
>> (and always quite strong, typically over 0 dB), and at 100-Hz intervals
>> below it progressively weaker spots of the same station appear.  Here's an
>> example:
>>
>> My setup:  Carolina windom to Clifton Labs 11 dB preamp to AM and FM
>> broadcast band filters, then to an RP-16.  Software-wise I'm running
>> Demin's SDR receiver to CWSL_Tee to CWSL_SSBWave.exe to WSJT-X.
>>
>> I'd like to know if anyone else is noticing this.  I've only seen it
>> since I started using the RP-16.
>>
>> --
>>
>> 73, Pete N4ZR
>> Check out the Reverse Beacon Network
>> at <http://reversebeacon.net> <http://reversebeacon.net>, now
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
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