[CQ-Contest] Question re Interstation interference

[Bill Coleman]

On May 30, 2005, at 10:02 PM, W1HIJCW at aol.com wrote:

> Interference between stations was almost nil ... due to some superb
> installation and engineering by the station owner for all the  
> stations and antennas ...
> except for one particular pair, 10M and 15M. When the 15M station was
> transmitting at roughly 1KW, anywhere between .000 and .075, and  
> the 10M station was
> listening anywhere between 28.0 and 28.1, there was a strong signal  
> from the
> 15M station. Now here's the strange part ... the interference  
> sounded like a
> pure CW note, EXCEPT that changing frequency on the 10M radio, or  
> for that
> matter on the 15M radio, made no difference to the note or apparent  
> signal
> strength. In other words, it sounded just like a sidetone signal.

At NQ4I, we ran into this same problem with the 15m mult station and  
the 20m run station. When 20m transmitted, there was a low-level  
signal that would not respond to tuning.

The cause had to do with the close proximity of the 20m run and 15m  
mult antennas. This signal did not appear on the 15m run station,  
however. All three stations were using nearly identical rigs. (All  
FT-1000MPs)

The cure, as we discovered, was to use a 15m bandpass filter on the  
front end of the rig. We were able to experiment with the filter from  
the run station. Completely eliminated the interference.

I've since built a set of 5 filters for all of Rick's mult stations,  
which we'll deploy this next contest season.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901