Topband: Single antenna port xcvr but want to employ separatereceive antenna

[Tom W8JI]

> Anyone have an RTR-1 or 1A that is excess to their needs and willing to 
> sell OR have another idea of how I can employ a separate receive antenna 
> when I have one antenna port?
> Thank you, in advance, for any replies....off line replies work for me.
> 72/73, Jim Rodenkirch K9JWV



Be REAL careful how you do this, Jim!!!! What works for one radio or system 
will not always work for another. This is highly radio (and even amplifier) 
dependent. I can say that based on some very good field experience in how 
things interface. (I'm actually looking at newer radios today to check their 
control systems.)


Many radios only have a few milliseconds between the low signal and the RF 
output, some don't have any time between the TX signal and the RF output. 
You have to get any relay completely transferred and all of the bounce gone 
before RF appears.  Normally the "back to receive" end of the sequence is 
not a worry.

Many radios do not have the best timing for the external amplifier relay 
control ports. Some amplifiers do not like other stuff hanging on the TX 
control line.

If you pull a relay low to go TX and you ever lose power to the relay, lose 
the relay, or lose the relay path, the system defaults with the transmitter 
running into the receiver antenna. You have to decide if that can damage RX 
antenna stuff. This requires a fast relay pull in time, and a slow release 
time..

The solution seems to be to release a relay to go from RX antenna to the TX 
antenna, but this system requires a very fast release time and sometimes a 
slower actuation time. This means we cannot use a backpulse diode because it 
will slow the relay too much, and it will go into TX mode after the RF 
appears.

In all cases the relay has to be pretty fast compared to the radio's window 
between pulling the TX line low and outputting RF. If the relay is ever 
mid-way in transfer, still bouncing, or in the wrong position when RF 
appears, the least that happens is broadband transfer clicks. The most is 
usually damage to the RX antenna.

If there is a reasonable way to do it, it is better to add a RX port in the 
radio and avoid all this. :)

73 Tom