[Elecraft] OT - operating QRP at same park

[Jim Brown]

On Sun,4/16/2017 9:44 AM, kevino z wrote:
> Would the use of some bandpass filters have helped us?

Maybe. It depends on whether you were hearing the other radio itself, or 
intermod created by some nearby non-linear device that re-radiated it. 
Bandpass filters will take care of the other radio, but not the 
intermod. 30-40 ft is pretty close, even for 10W and KX2s.

> This is a situation we are trying to resolve before operating QRP in a similar park for a QSO party.
>
> If more distance between the antennas would have helped, what is the proper way to determine the needed separation?

If you're hearing the other radio, RF loss in the path between the two 
antennas can be computed using NEC. To do that, put both antennas in the 
model, put a Source at the feedpoint of one antenna, put a 50 ohm load 
at the feedpoint of the other antenna (but no source). Set NEC to 
compute for 10W (or whatever power you want to run). Then compute the 
pattern, and click on Load Data to see how much signal is induced at the 
other antenna.

BUT -- another issue comes to mind. You say "resonant end-fed antennas." 
All antennas need some form of return conductor for antenna current. 
What form do your antennas take? What's the return for antenna current?  
Is it the coax?  If so, is there a ferrite choke at some point so that 
current is confined to the intended length? How close are the rigs? And 
when you build that NEC model, be sure to include that coax and any 
other counterpoise.

73, Jim K9YC