[CQ-Contest] 10/15 interaction

Bill Hider n3rr at erols.com
Thu Nov 6 12:50:09 EST 2014


Intuition usually is insufficient compared to engineering.

Earlier this year, I purchased a complete design and fabrication of a stub
filter package from Top-Ten devices for my SO2R station.
George, W2VJN designed and fabricated my system then shipped it to me for my
I will soon be adding a new page to my Website where I'll describe the
entire process.

But it all started with my reading a local ham's copy, then purchasing and
studying my own copy of George's book:
"Managing Interstation Interference, Revised Second Edition"
by George Cutsogeorge, W2VJN
Which is available from INRAD.Net and Array Solutions and probably other
It cost me all of $20.00.

More to your point:  
I, too,  have 10M and 15M monobanders mounted on the same mast with 13 feet
vertical separation.
You can see this and my other 8 monoband antennas for the 6 HF contest bands
on two towers on my website: www.erols.com/n3rr
During contests, I have virtually no interference between the transmitting
radio and the receiving radio on another band.

By examining your interstation interference environment, per George's book,
you can determine quite accurately where the interference is coming from and
how much interference (in dBm)
is present in your system.  Then, you may design and implement the
appropriate filters.

But, buying a hi-pass filter without first performing the appropriate
engineering is not the right approach, in my opinion.

One more level of info, Randy:  By implementing a 15m reject filter in the
10m transmit path and a 10m reject filter in the 15 m receive path
you  get "double" effectiveness.  I put "double" in quotes, to emphasize
that it's two paths of filtering, not necessarily 2x the dBm.
It's to give you another way to think about solving your interference
problem.  You may not need both filters, BUT if you
perform the engineering analysis first, you will know what you actually

George performed the analysis of my SO2R interference environment via email
with me in MD and he in OR.
He gave me the testing parameters and setup.  I performed the tests on my
station and sent him the data.
All as if he were the laboratory engineering  manager and I was his
technician in his lab making the measurements as he directed!
He then performed the analysis & determined the stub filter design I would
need and quoted it to me.

ALL FYI for you and the reflector.

Disclaimer:  I have no business relationship, except as a customer, with any
companies or people mentioned in the email.

I am available to answer any questions you or anyone may have.


Bill, N3RR

-----Original Message-----
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of
Randall K Martin
Sent: Thursday, November 06, 2014 10:19 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 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

Randy K0EU

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