[Elecraft] OT - operating QRP at same park

[Jack Brindle]

I believe Jim’s “BUT —“ is something being overlooked by a lot of folks here. The fact is that the It certainly enters into the situation as a major contributor since the antenna does extend onto the feedline for end-fed antennas (all the way to the radio!). Essentially, everything that is not decoupled is part of the antenna radiator. That’s why Jim’s point about ferrites is so important.

I would suggest that the situation would be greatly different if the antennas were sloping dipoles resonant on each band, and even better if decoupling ferrites were used at the feed points of the dipoles.
End-fed antennas may be easy to put up, but that comes at a cost. Especially at QRP, proper engineering fundamentals are very important!

Playing with Jim’s NEC model suggestion sounds very interesting.

- Jack, W6FB

> On Apr 16, 2017, at 10:24 AM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
> 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
> 
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