[CQ-Contest] 10/15 interaction

Tod Olson tod at k0to.us
Thu Nov 6 11:46:19 EST 2014

I solved a similar problem last weekend. When operating with high power on
15m there was a very high level of 15m RF on the 20m feed line going to
the second station (SO2R). By adding a stub [open] in the 20m feed line I
was able to dramatically reduce this 15m RF. The stub did not detune the
20m input, but it reduced the 15m component that had been reaching the
station via the 20m feed line to a very small amplitude. It was well
within the ability of the Dunestar 600 filter to reduce to a level that
was essentially not detectable when listening on 20M. In my case operating
on 15m caused the original problem but operating on 10m did not.I expect
that I could put a stub [or stubs] into each of the feed lines should it
be necessary to reduce the captured RF from transmitting on a different

My antenna for these bands is a Force 12 C31-XR which has the 10, 15 and
20m antennas interlaced on the same boom, but with independent feed lines.

On 11/6/14, 9:18 AM, "Randall K Martin" <rkmassoc at comcast.net> wrote:

>Over the years, I've managed to clean up most of the cross band
>interference that occurs when I operate my SO2R station running high
>power. The one exception is that I cannot use my 10M monobander to
>transmit while receiving on my 15M monobander. This is not surprising,
>since they are only separated vertically by about 8 feet. Transmitting
>on 10M must be dumping significant power back into the 15M transmitter
>(an elecraft K-3) since it causes the COR relays to click and I get the
>"HI RFI" error. When this happens, I immediately stop transmitting and
>flip the 15M rig over to a tribander on a second tower. Normally, I'm
>able to remember not to do this, but in the heat of a contest, I forget.
>What I find odd is that I can transmit on the 15M monobander while the
>second radio is connected to the 10M monobander and there is no "HI RFI"
>problem. In fact, very little interference.
>Here's my question. I'm contemplating purchasing a high power band pass
>filter (4O3A) to prevent the interaction. I'd prefer not to buy both a
>10M and a 15M filter if I don't have to. My intuition tells me that I
>should be able to add the filter to the 10M transmitter. Any thoughts on
>this? Is there some other path in which the RF could be reaching the 15M
>rig that would render the band pass filters ineffective?
>I have dunestar 100W band pass filters on both rigs, placed between the
>rig and the amp. I know that adding separation between the monobanders
>would help, but my tower configuration isn't really amenable to adding
>more separation.
>Randy K0EU
>CQ-Contest mailing list
>CQ-Contest at contesting.com

More information about the CQ-Contest mailing list