Here's part of the SWR/Low Pass Filter board circuit description from
the Argosy II manual:
"PIN diodes D3 and D4 connect the antenna to the receiver input when
receiving, and are back biased by a voltage rectified at D1 and D2 when
transmitting. The transmitted signal on its way to the antenna first
passes through the primary of transformer T1 in the SWR bridge. /This
bridge is balanced on 28 MHZ by setting the trimmer capacitor so that
there is a null on the meter when a 50 ohm resistive dummy load is
connected to the antenna jack /and the FWD/REV switch is in the REV
position. Reflected power is sensed through D9, filtered to a dc
component and applied to the meter by way of the REV terminal. R1, in
series with this meter, is adjusted for a three to one SWR meter
indication when the load is changed to 150 ohms.... Forward power for
driving the front panel meter is rectified and converted to a DC
control voltage through (diodes) D7 and D8. This voltage is also fed to
the ALC pin on the RF/MIXER board..."
Well, by adjusting the bridge balancing trimmer cap just off the null, I
was able to cure the circuit breaker tripping symptom. This indicates
to me that the fault is in the ALC circuit since changing its source
voltage eliminates the problem. Of course, the SWR bridge is now
unbalanced, so something is still amiss.
What do you think?
73 and thanks,
Craig
W3CRR
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