[CQ-Contest] 10/15 interaction
k6ll.dave at gmail.com
Thu Nov 6 12:48:43 EST 2014
The problem is that too much 10M energy is coming down the 15M
feedline. Adding additional filtering to the 10M transmitter
won't solve that problem. What you need is more filtering on the
15M feedline to reject the 10M RF. The first thing I would try
is a coax stub on the 15M feedline. Try a 1/4 wave 40M shorted
stub, about 23' long, made from RG-213. A stub like that will
pass 40 and 15, and will reject 20 and 10. Tune it with a GDO,
optimizing it for 10M.
I have a Ten-Tec amplifier whose QSK circuit trips when another
amp is transmitting on 20, and that exact stub cured the problem.
That amp is only used on 15 and 40, so the stub works out fine.
It is also possible that the length of the feedline on the 15
just happens to tune the 15 driven element to 10 meters. Try
adding 1/8 wavelength (at 28MHz) of feedline to the 15M feedline.
That's about 4 feet.
You could also buy another 15 meter receive filter, and cascade
it with the other one. I conducted such an experiment one time,
and the additional rejection was significant, but not 2X. As I
remember, it was about 1.5X.
Dave Hachadorian, K6LL
From: Randall K Martin
Sent: Thursday, November 6, 2014 8:18 AM
To: cq-contest at contesting.com
Subject: [CQ-Contest] 10/15 interaction
Over the years, I've managed to clean up most of the cross band
interference that occurs when I operate my SO2R station running
power. The one exception is that I cannot use my 10M monobander
transmit while receiving on my 15M monobander. This is not
since they are only separated vertically by about 8 feet.
on 10M must be dumping significant power back into the 15M
(an elecraft K-3) since it causes the COR relays to click and I
"HI RFI" error. When this happens, I immediately stop
flip the 15M rig over to a tribander on a second tower. Normally,
able to remember not to do this, but in the heat of a contest, I
What I find odd is that I can transmit on the 15M monobander
second radio is connected to the 10M monobander and there is no
problem. In fact, very little interference.
Here's my question. I'm contemplating purchasing a high power
filter (4O3A) to prevent the interaction. I'd prefer not to buy
10M and a 15M filter if I don't have to. My intuition tells me
should be able to add the filter to the 10M transmitter. Any
this? Is there some other path in which the RF could be reaching
rig that would render the band pass filters ineffective?
I have dunestar 100W band pass filters on both rigs, placed
rig and the amp. I know that adding separation between the
would help, but my tower configuration isn't really amenable to
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