[TangerineSDR] Frequencies for FT8 & WSPR

[Phil Erickson]

Hi Bill,

  I think you should be setting the mode to USB and the dial to 7.074 MHz
(example for 40 meters).  The DE, if it is doing true USB, will keep the
upper sideband and reject the lower one.  (There are multiple methods, but
the coherent phasing method is perhaps easiest when you have guaranteed I/Q
that are 90 deg out of phase.). You can play with that yourself by finding
a web SDR and setting it up that way.  See attached screenshot.

73
Phil W1PJE

On Wed, Nov 25, 2020 at 11:50 AM Engelke, Bill via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:

> Hello All:
>
>
>
> A week ago in the TangerineSDR telco, we touched on an issue regarding
> frequencies for FT8 and WSPR. I’m interested to know what folks think about
> what should be done here.
>
>
>
> The question is this:  when setting the Data Engine (i.e., the radio part)
> to a frequency for FT8 or WSPR reception, we have used the term “center
> frequency,” thus suggesting we might set the DE to the center of the
> respective sub-band (see table below). Perhaps that is compatible with IQ
> sampling, where we recognize the frequency of the signal by the phase
> difference between I and Q; so signals below the center would have a
> negative phase shift (“negative frequency”), signals above a positive shift.
>
>
>
> I have a question:
>
>
>
>    - The decoders for both WSPR and FT8 assume the receiver is set to a
>    dial frequency (per the WSPR and FT8 band plans) and receiver is in USB.
>    This produces a baseband signal (that can be collected by a sound card) in
>    the audio range. I am fuzzy on the correct way to convert this signal – do
>    we set the DE’s frequency to the dial frequency and assume that the decoder
>    will ignore everything in the negative frequency area, or do we set the
>    DE’s frequency to the center of the sub-band?
>    - Just as a note, Scotty and Martin, who are planning to do the FPGA
>    programming, voiced some concerns about whether the DE could actually be
>    set to the required frequency (be it “dial frequency” or “center of the
>    sub-band”), due to open questions about the clock’s output (?) – I am fuzzy
>    about the details here, but as recall, the way we left it was that Scotty &
>    Martin are going to have a look at the Pavel Demin FPGA code to see how he
>    accomplished it (which may answer the question above). What I do know is
>    that the Raspberry Pi does not have the capacity to accept a wide-band data
>    feed( (i.e., encompassing all FT8 & WSPR frequencies) and doing the
>    filtering to slice out the sub-bands for the decoder; that would take a
>    high-end desktop.
>
>
>
> If anyone has any thoughts, please post. Below is the table of frequencies:
>
>
>
> *Frequencies for FT8*
>
>
>
> (4000 samples/sec)
>
>
>
>
>
> Dial Freq. in MHz
>
> in Hz
>
> lowest signal
>
> center
>
> top of band
>
> 1.84
>
> 1840000
>
> 1840200
>
> 1841500
>
> 1843000
>
> 3.573
>
> 3573000
>
> 3573200
>
> 3574500
>
> 3576000
>
> 7.074
>
> 7074000
>
> 7074200
>
> 7075500
>
> 7077000
>
> 10.136
>
> 10136000
>
> 10136200
>
> 10137500
>
> 10139000
>
> 10.074
>
> 10074000
>
> 10074200
>
> 10075500
>
> 10077000
>
> 18.1
>
> 18100000
>
> 18100200
>
> 18101500
>
> 18103000
>
> 21.074
>
> 21074000
>
> 21074200
>
> 21075500
>
> 21077000
>
> 24.915
>
> 24915000
>
> 24915200
>
> 24916500
>
> 24918000
>
> 28.074
>
> 28074000
>
> 28074200
>
> 28075500
>
> 28077000
>
> 50.313
>
> 50313000
>
> 50313200
>
> 50314500
>
> 50316000
>
> 50.323
>
> 50323000
>
> 50323200
>
> 50324500
>
> 50326000
>
>
>
>
>
>
>
>
>
>
>
> *Frequencies for WSPR*
>
>
>
> (375 samples/sec)
>
>
>
>
>
> Dial Freq. in MHz
>
> in Hz
>
>
>
> center
>
>
>
> 0.136
>
> 136000
>
>
>
> 137500
>
>
>
> 0.474
>
> 474000
>
>
>
> 475500
>
>
>
> 1.8366
>
> 1836600
>
>
>
> 1838100
>
>
>
> 3.5686
>
> 3568600
>
>
>
> 3570100
>
>
>
> 7.0386
>
> 7038600
>
>
>
> 7040100
>
>
>
> 10.1387
>
> 10138700
>
>
>
> 10140200
>
>
>
> 14.0956
>
> 14095600
>
>
>
> 14097100
>
>
>
> 18.1046
>
> 18104600
>
>
>
> 18106100
>
>
>
> 21.0946
>
> 21094600
>
>
>
> 21096100
>
>
>
> 24.9246
>
> 24924600
>
>
>
> 24926100
>
>
>
> 28.1246
>
> 28124600
>
>
>
> 28126100
>
>
>
> 50.239
>
> 50239000
>
>
>
> 50240500
>
>
>
>
>
>
>
> -73- Bill , AB4EJ
> --
> TangerineSDR mailing list
> TangerineSDR at lists.tapr.org
> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>


-- 
----
Phil Erickson
phil.erickson at gmail.com
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