Locked Re: Frequency shifting on #WSJTX_config #windows11 #Windows10

Martin G0HDB <marting0hdb@...>

On Wed, Apr 27, 2022 at 11:13 PM, goroberts56 wrote:

That was it. I had fake it turned on and when I turned it off it went back to
what I considered normal. I noticed that when I turn it on with my Flex, it
shifts even more. My understanding is that the software will take advantage of
the audio properties of the given radio so this is not a problem but a
feature. Now that I know this, I can sleep at night again. Thanks everybody
for their comments.

The advantage of using the 'split' mode with either 'Rig' or 'Fake It' selected is that the software ensures that the audio signal that's fed to the Tx is maintained within the 'sweet spot' range of 1500 to 2000Hz thus ensuring that any harmonics of the audio are (probably) outside the audio passband of the transmitter.

Here's a worked example:

If you have the Tx cursor on your waterfall positioned within the range 1500 to 2000Hz then the software won't adjust the rig's VFO frequency during transmissions. However...

If you set your Tx cursor to say 1200Hz, ie. outside the 'sweet spot' range, then at the start of a transmission the software will shift the rig's VFO down by 500Hz but will also shift the audio output signal up by 500Hz to 1700Hz, ie. back into the 'sweet spot' range, thus ensuring that the actual RF output frequency is still at the desired 1200Hz above the dial frequency of 14074kHz or whatever.

Similarly, if you position your Tx cursor at 2200Hz the VFO will be QSYed up by 500Hz and the audio will be shifted down by 500Hz, ie. back into the 'sweet spot' range, and again the actual RF output frequency will be the desired 2200Hz above the dial frequency.

If you position your Tx cursor even higher or lower on the waterfall then the software will again adjust the rig's VFO frequency up or down, in increments of 500Hz, and will again generate the audio signal within the 'sweet spot' range of 1500 to 2000Hz.

If you don't use one of the split modes, either 'Rig' or 'Fake It', then you run the risk of possibly allowing harmonics of the audio signal to be transmitted because they fall within the passband of the Tx filtering, coupled with the likelihood of audio at or near either the lower or upper corner frequencies of the Tx filtering being heavily attenuated and thus reducing the RF output power level.

IMO it's very much better to use whichever split mode works best for you - I've always used 'Fake It' with the various Icom rigs I've owned over the years.


Martin G0HDB

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