Pistar RX offset etc.

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F6GVE
Posts: 84
Joined: Sat Nov 16, 2019 8:52 am

Pistar RX offset etc.

Post by F6GVE » Sat Jul 18, 2020 1:18 pm

I've been able to fine-tune the transmission frequency in FM mode of my 2 old GD77's and my new DM-1801
With the frequency meter drived by satellite, I finally got +25 Hz, +35 Hz, +20 Hz after warm-up so I can consider that my 3 HT are correctly and identically tuned.

The DM-1801 is used for the hotspot function.
Obviously the TXoffset is set to 0 in Pistar.

When I transmit with either my GD-77's, If I logically set the RXoffset to 0 too, my BER si bad and fluctuates a lot.
In Pistar I have to set the RXoffset to -900 or -1000 to have the best BER, which is 0 or 0,1%
The RXoffset value is not critical at all, but I found -900/-1000 to be the best choice.

If I replace the GD-1801/hotspot with a GD77, I have to maintain this -900/-1000 RXoffset in Pistar too.

So I tend to assume that there is an offset between the transmit and receive frequencies?

(I wanted to low the RX frequency of all my DMR channels by 1 kHz in the CPS but it is not possible as the CPS rounds up to the nearest 2,5 kHz)

VK3KYY
Posts: 7484
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: Pistar RX offset etc.

Post by VK3KYY » Fri Aug 07, 2020 10:44 pm

Do not use offsets with hotspot mode.

That feature is only in PiStar because the Jumbospot style hotspots have terrible frequency control, and need to be adjusted.

DMR radios are always very accurately calibrated at the factory, and hence you should not use an offset

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