[CQ-Contest] 10/15 interaction

Tod tod at k0to.us
Thu Nov 6 14:53:18 EST 2014


My guess is that 1) will do the job. 

2) will only  improve things if the undesired 15m signal is on the outside shield of the coax. In that case the choke might work at the station end and save you a trip up the tower. 

I agree  that 4) is not a solution to run after. If you do however, contact me -- I have been curious about how well K3's might work. A used pair might be interesting to test.

A bit of additional information-

 I used my AIM4170 to scan the frequencies of interest on the feed line after the stub. That allowed me to be certain that the stub did not negatively affect the VSWR at the desired frequency. I could also see when the length of the stub produced the maximum effect on 15m impedance. I did not even measure the physical length of the stub -- I just found a length that seemed to do the job according to the scan and when I tested it running the amp it clearly was working.

73, Tod, K0TO

Sent from my iPhone 6

> On Nov 6, 2014, at 11:33 AM, Randall K Martin <rkmassoc at comcast.net> wrote:
> Wow,
> Thanks for all the quick responses. Here is a summary of what I've heard so far.
> 1) I am already using coax stubs on both the 10M and 15M feedlines, and I believe these are working. I do not have a 15M reject stub on the 10M feed, so this is a good suggestion and I will try it.
> 2) Kelly VE4XT had a good suggestion to add a choke balun on the 10M yagi in addition to the standard KLM balun that is already in place to see if this will help. The 10M feedline runs down through the plane of the 15M yagi. WX is nice here and I can easily try this.
> 3) There may be less interaction when the yagis are 90 degrees from each other, but in almost all situations, I am pointing them in the same direction. Also, my goal is to eliminate the HI RFI problem from happening in any scenario.
> 4) Getting rid of the K-3's is not something I would consider.
> 5) The antennas are both 6 element KLM big stickers, both with standard KLM feed baluns of that era.
> 73 Randy K0EU
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