[hpsdr] New T/R Switch for >100W without external blocking voltage.

[Kjell Karlsen]

Hi All.

I have uploaded 2 files to HamSDR. One is an update of the schematic for  
ApolloRev4 and one is a 100W T/R Switch without any external blocking  
voltage.

Using an electronic T/R Switch at power >50W normally needs an external  
voltage of 150V or more to give enough isolation for the RF signal to the  
RX. When I worked with Apollo, I discovered that by using the negative  
voltage detected by one of the diodes in the switching path to the RX, it  
was possible to get better attenuation of the RF to the RX during TX. This  
detected voltage is the peak of the RF and added to the +12V, the blocking  
voltage is around 70V at 50W.

For higher power levels, a higher voltage is needed. By using a voltage  
doubler, the detected voltage is >200V and this is sufficient for a 150W  
T/R Switch.

By using components with higher ratings, it may be possible to use this  
principle also for higher power levels.

73, Kjell.

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