Re: [wsjt-devel] Dial calibration errors

[Edson W. R. P. <ewp...@gm...>]

Hi Joe,

Would it add too much complexity to have the frequency error correction in
the audio base band of the decoders? This would prevent having to re-tune
the rig and would also allow crystal controlled transceivers to also have
frequency error correction.

73, Edson PY2SDR

---
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On Wed, May 13, 2015 at 11:48 AM, Joe Taylor <jo...@pr...> wrote:

> Hi all,
>
> One of the fun things about WSPR is the frequency accuracies that
> are involved.  Having WSPR mode in WSJT-X motivates some serious thought
> about how best to handle frequency calibration errors in transceivers.
>
> Typical dial readout errors in modern radios are a few parts per million
> -- for example, a 20 Hz error at 14 MHz.  For JT65 or JT9 such
> discrepancies are not very important.  But the WSPR sub-bands in
> conventional use since 2008 are only 200 Hz wide, and we'd like to use
> all of that range effectively.  If my transceiver's dial reads 20 Hz
> low, and yours reads 20 Hz high, and we both set our dials to the
> conventional 14.0956 MHz for 20 meters, after setting our WSPR Tx
> frequencies at random within the 200 Hz sub-band there's something like
> a 20% chance that we won't decode one another.
>
> Earlier production versions of WSPR have handled these issues in a
> rather sophisticated way.  The User's Guide includes detailed
> instructions for determining calibration constants for your transceiver
> using over-the-air signals (see Appendix C of
> http://physics.princeton.edu/pulsar/K1JT/WSPR_3.0_User.pdf ).  The
> resulting accuracies can be better than 1 Hz.
>
> If CAT control is in use and  "Enable frequency correction" is ticked on
> WSPR's "Advanced Setup" window, frequencies sent to the radio are
> adjusted so as to compensate for the dial errors.  For example, if
> 14.0956 MHz has been requested, the command for 14095620 Hz may be sent
> to the radio.
>
> I picture this being implemented in WSJT-X in a similar way.  In this
> example, the radio dial would read 14.096520.  I'm suggesting that the
> frequency readout on the WSJT-X screen would read 14.095600, the
> supposedly "true" frequency.
>
> Comments and suggestions would be welcome.
>
>         -- 73, Joe, K1JT
>
>
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