[hpsdr] Apollo schematics

[Kjell Karlsen]

Hi Roland.

There are in fact 2 T/R switches her: If you install RL33 you do not  
inctall any of the other components. But many people want an electronic  
T/R switch (no relay rattle). Then you install all components except the  
relay.

T41 and T42 is the switch between RX and TX (DC). When /PTT is open, T42  
is ON and T42 OFF, there is current in D47 and D48 so they are ON and D46  
is biased with 12V so it is OFF. This permits the signal from ANT (via the  
LP filters) to the RX to pass with very little loss (<0,5dB). At the same  
time D9 is also biased OFF by R26.
When /PTT is grounded, T41 is ON and T42 OFF. Now there are current (DC)  
through D46 so it is ON and D47 and D48 are biased to OFF. RF is  
effectivly grounded between D47 and D48 by D46 and C221. At the same time  
T43 is switched ON, effectivly grounding the cathode of D9 (DC) and there  
is current flowing through D9 so it is ON (RF) The signal from the TX can  
now pass through D9 to the antenna (via the LP filters)with <0,5dB loss.

This circuit is partly copied from Elecraft K3 and may be uset for power  
levels up to 25W. It can also be used on 100W, but then we must include a  
higher voltage (70-80V) to bias D47 and D48 OFF to prevent the TX signat  
 from reaching the RX. The attenuation of the T/R switch is >60dB in RX at  
50 MHz.

73, Kjell.




På Sat, 19 Dec 2009 08:58:31 +0100, skrev roland etienne  
<roland.etienne at free.fr>:

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