Adjusting the RX frequency, independent of the TX frequency

OK1TE
Posts: 58
Joined: Tue Sep 29, 2020 7:58 am

Adjusting the RX frequency, independent of the TX frequency

Post by OK1TE » Sat Dec 12, 2020 8:30 am

Hello,
the documentation says:
"If different TX and RX frequencies are set, and the currently selected input is set to RX, changing the RX frequency will also change the TX frequency, and the difference between the RX and TX frequency will be maintained if possible."

Please, is there any way to lock also the TX frequency while tuning RX? It's a recommended way to work some cross-band satellites and the ISS repeater, as the Doppler shift on TX (on lower band) is not so serious as in the RX (higher band) case which is worth to adjust.

VK3KYY
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Location: Melbourne, Australia

Re: Adjusting the RX frequency, independent of the TX frequency

Post by VK3KYY » Mon Dec 14, 2020 8:57 pm

No.

I'm afraid there is currently no ability in the firmware to lock the Tx while changing the Rx.

That function could be added, but there would need to be a User Interface to control the locking mode between Rx and Tx.

I guess this would need to be added to the Options menu, perhaps "T/R F Lock:On" or "T/R F Lock:Off"

Often the most complex thing when implementing new features if the settings user interface, because the total screen width is 16 characters, and options need to be translated into 13 languages.
Also there needs to be a voice prompt for all settings.


Please can you explain the use of this for satellite operation.

N1KY
Posts: 84
Joined: Sun May 24, 2020 10:46 pm

Re: Adjusting the RX frequency, independent of the TX frequency

Post by N1KY » Mon Dec 14, 2020 11:22 pm

Doppler shift is proportional to frequency. When working a station via a satellite VHF/UHF cross band repeater the amount of doppler shift compensation needed is different for the uplink frequency than the downlink frequency.

During a satellite pass it would be extremely useful to be able to quickly bump the RX frequency as needed without it also changing the TX frequency.
Last edited by N1KY on Tue Dec 15, 2020 4:17 am, edited 1 time in total.

G4EML
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Re: Adjusting the RX frequency, independent of the TX frequency

Post by G4EML » Tue Dec 15, 2020 12:13 am

Coupling the RX and TX frequencies is really there to cope with repeater offsets in the same band so you can tune between repeaters without needing to reset the transmit frequency.

It is probably less useful (or maybe not needed at all) if the RX and TX are on different bands.

So the logic could probably be changed to only track the RX and TX frequencies if they are in the same band. That would allow cross-band satellite use as described.

Colin.

VK3KYY
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Location: Melbourne, Australia

Re: Adjusting the RX frequency, independent of the TX frequency

Post by VK3KYY » Tue Dec 15, 2020 7:10 am

Thanks everyone

I think it would better to have this as an option, rather than turning off the locking if the Tx and Rx are not in the same band.
As hiding the functionality differences is when operating cross band is likely to cause confusion.

I think the default would need to be the same as it is at at the moment, where Tx and Rx are locked together, as this is valid for both simplex and repeater operation.

OK1TE
Posts: 58
Joined: Tue Sep 29, 2020 7:58 am

Re: Adjusting the RX frequency, independent of the TX frequency

Post by OK1TE » Tue Dec 15, 2020 3:10 pm

VK3KYY wrote:
Mon Dec 14, 2020 8:57 pm
That function could be added, but there would need to be a User Interface to control the locking mode between Rx and Tx.

I guess this would need to be added to the Options menu, perhaps "T/R F Lock:On" or "T/R F Lock:Off"
Thank you. Before I asked here, my first intuitive try was to press SK2+Up, as SK2+Down "locks" the Rx freq. Wouldn't this be an intuitive way how to implement the feature?

VK3KYY
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Location: Melbourne, Australia

Re: Adjusting the RX frequency, independent of the TX frequency

Post by VK3KYY » Tue Dec 15, 2020 8:31 pm

OK1TE wrote:
Tue Dec 15, 2020 3:10 pm
Thank you. Before I asked here, my first intuitive try was to press SK2+Up, as SK2+Down "locks" the Rx freq. Wouldn't this be an intuitive way how to implement the feature?
That won't work.

SK2 + Up and Down, are already assigned. That key combination changes active input field between Tx and Rx when you are entering the value manually.

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: Adjusting the RX frequency, independent of the TX frequency

Post by VK3KYY » Tue Dec 15, 2020 8:38 pm

Before I consider implementing this function...

For satellite operation, is there any benefit to step the Tx and Rx frequencies in opposite directions.

e.g. Pressing the Up arrow would increase the Rx frequency, but decrease the Tx frequency.

This would need to be an addition part of this Rx/Tx freq control mode, i.e the settings for "Tx/Rx F lock" could be

"On" (default)
"Off" (Tx and Rx are independant)
"Sat" (Satellite operation where Tx and Rx frequency steps are opposite).
Also in Satellite mode, I could reduce the step size by perhaps a factor of 10, so that the steps would be

250Hz,500Hz,625Hz,1kHz,1.25Khz,2.5Khz,3Khz,5Khz

Note.
I can't add more steps because of the codeplug format does not allow it. But I could scale the steps.

N1KY
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Re: Adjusting the RX frequency, independent of the TX frequency

Post by N1KY » Wed Dec 16, 2020 3:59 pm

VK3KYY wrote:
Tue Dec 15, 2020 8:38 pm
For satellite operation, is there any benefit to step the Tx and Rx frequencies in opposite directions.
No benefit than I'm aware of.

VK3KYY
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Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: Adjusting the RX frequency, independent of the TX frequency

Post by VK3KYY » Wed Dec 16, 2020 10:05 pm

N1KY wrote:
Wed Dec 16, 2020 3:59 pm
VK3KYY wrote:
Tue Dec 15, 2020 8:38 pm
For satellite operation, is there any benefit to step the Tx and Rx frequencies in opposite directions.
No benefit than I'm aware of.
Thanks

That's roughly the same information that I received from other people.

Technically the Doppler shift does need to be applied to the Tx freq, but the Doppler effect on VHF is much less than on UHF, so the change would need to be 1/3 of the change on the UHF freq

So this won't be implemented.


I have been told however, that smaller step sizes (than 2.5kHz) may possibly be beneficial.

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