[Elecraft] Diversity receive and isolating antennas

[Wayne Burdick]

Hi George,

If you have an RF voltmeter or milliwatt meter, try terminating the  
proposed RX antenna in a dummy load, then measure the voltage or power  
when you transmit. If it's less than about 2.23 Vrms (100 mW, or +20  
dBm), you'll have no trouble at all.

The subreceiver (as well as the RX ANT IN jack) can generally handle  
far more than this without damage; I pumped several watts in during  
early testing. But you don't want to take risks in the field, or have  
the COR (carrier operated relay) switching in and out during keying in  
CW mode. Antennas can change pattern due to wind, rotation, etc.

If the power at the AUX RX input (sub receiver) looks like it may be  
excessive, you can take additional precautions. You could move the RX  
antenna farther away, put it in a null of the TX antenna, reduce its  
gain (length), or use the KEY OUT line to drive an external shunt PIN  
diode switch.

73,
Wayne
N6KR


On Jun 24, 2010, at 10:04 AM, George A. Thornton wrote:

> I am planning to use my dual receive K3 for field day and we want to  
> try
> out diversity receive.
>
>
>
> This particular setup will be for 20 meters only.  The primary antenna
> will be a 20 meter monoband Yagi mounted on a 40-60 ft. tower.
>
>
>
> We were considering using a Buddipole mounted in vertical position and
> tuned for 20 meters voice to serve as a Rx only antenna for the sub.
> All transmission will be from the Yagi.  I was planning to hook the
> Buddipole into a Rx only connector.
>
>
>
> We will do the best we can to isolate the two antennas but having not
> been to the site before I am not sure what will be possible in the way
> of geographic isolation.
>
>
>
> I want to make sure I won't do any damage to the K3 in case the
> isolation is not sufficient.
>
>
>
> Anyone familiar with this situation able to give me some guidance?
>
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