[1000mp] RX ANT

[Tod - ID]

This is good anecdotal data. 

> At our operation locations for the various 160 Meter 
> contests, we run two and sometimes three MP's simultaneously. 
>  We will always have the RUN/CQ transmitter going while the 
> other one/two MP's are in the HUNT/receiving mode and 
> likewise the RUN/CQ transmitter will be listening while 
> either of the HUNT transmitters is transmitting.
> 
> In all cases we use multiple Beverages feeding the separate 
> RX jack on the rear of the MP's.  Throughout many years and 
> dozens of contests there NEVER has been any problem with 
> overload of, OR damage to, the MP receivers.
> 
> YMMV, and good luck.  CU all in the CQ 160 SSB tonight and 
> tomorrow night from N7GP, Greenlee County and DM52, in Arizona.


I have gotten out the Service Manual and looked at the somewhat larger
diagrams it has. There does seem to be the possibility that relay, RL1001,
is affected when transmitting if the RX antenna has been selected for
listening. We do know that the {A/B} and {RX} lights on the front panel
change as one keys the transmitter. Maybe some else would like to trace the
control paths for RL1001 to see just what happens when the relay has been
activated and then one transmits.

If RL1001 does change state when the radio is transmitting if [RX] has been
selected,  then the front end of the receiver will have exactly the same
configuration during transmit when the RX-IN antenna is selected as it has
when one of the coax antennas [A/B] is selected.  The only exposure to
'unusual' voltages from the RX-IN antenna would be that which is posed by
the contact gaps between the RX-IN contacts and the regular antenna
contacts. I have no Idea about the characteristics of that relay so I can't
make a comment on what that risk might be.

The regular coax antenna path from entry to the receiver front end has one
zener in it to ground that I could find and the L1030 and R1045 shunt to
ground that I mentioned in the earlier message on this topic. This circuitry
clearly is satisfactory for protecting the front end of the receiver when
there is no separate RX antenna and should be sufficient if relay RL1001
selects that state on transmit and the RX-IN voltage is insufficient to
flash across the relay contacts. 

We are missing some basic measurements from the anecdotal experiences of
disaster and 'no problem' so we really have no idea what the voltage stress
was when problems occurred.  

I guess we are left with making our own decisions (that was what we were
doing anyway) about adding something that grounds the RX-IN during transmit
and not bothering to make such an addition. Since I have already made the
investment and installation I will continue to ground that input on
transmit. Can't hurt and might help.

Tod, KØTO