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

[Björn Ekelund]

If US stations display a 100Hz offset it is obviously not from mains hum so
you may be on to something.

73,

Björn SM7IUN


Den ons 31 juli 2019 kl 16:08 skrev Alex Ranaldi <alexranaldi at gmail.com>:

> I am suspicious of the exact 100hz offset.  The FT8 freq deviation is
> 6.25Hz.  100/6.25 = 16, or 2^4.  Almost seems like some sort of digital
> thing, perhaps on the transmit or receive side.
>
>
>
>
> On Wed, Jul 31, 2019 at 10:03 AM Björn Ekelund, SM7IUN <bjorn at ekelund.nu>
> wrote:
>
>> 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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