R Shunt value setting

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VK2VD
 

Posts: 2
Joined: 29 Jun 2022, 03:20

R Shunt value setting

Post by VK2VD »

Hello Manuel & Guido
Many thanks for this great radio. I have enjoyed very much building and using and modifying to classic version.

My question is in reference to the R Shunt setting. I am aware it is the resistance between R7 & R8, this I can measure. Now how does this figure relate to the value set by R Shunt in the sandwich? I get with the default setting of 19 around 50-60% efficiency.. to get your efficiency level I need to set R Shunt to 22. Both units I have. They are similar. There is no reference to this setting in your video on tuning of RF section. I wonder if you could talk about this.

Regards

Richard
VK2VD
DL2MAN
 

Posts: 459
Joined: 30 Dec 2021, 19:18
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Re: R Shunt value setting

Post by DL2MAN »

Hi Richard,

RShunt is the resitance of the shunt PCB-trace, for Drain Current measurement on RF Board around U1 (INA219). It turned out, PCB Trace resistance is not as constant as we thougt it would be.

It is not intended to "fake" Efficiency, when there is none, but to have a possibility to "calibrate" your internal measurement, so it matches external measurements.

So what should you do with it ?

try to measure as exactly as possible:
- Input Voltage (Uin)
- Input Current at RX (Irx)
- Input Current at TX (Itx)
- Output Power (Pout)
Calculate Input Power by
Pin = Uin * (Itx - Irx)
Calculate Efficiency by
Eff = Pout / Pin *100%

Compare it with onboard measurement, and adjust RShunt Value in Menu, until displayed Efficiency matches your Calculated externally determined efficiency.

Usually this varys over frequency, so try to find a middle value, that works on all bands. Usually displayed accuracy can be adjusted to below 5% over all bands this way.

73 Manuel; DL2MAN
VK2VD
 

Posts: 2
Joined: 29 Jun 2022, 03:20

Re: R Shunt value setting

Post by VK2VD »

Hi Manuel
Thank you for the detailed response. That answers my question very well.
Most appreciated
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