[CQ-Contest] Question re Interstation interference

[Bill Coleman]

On Jul 17, 2005, at 8:34 AM, Bill Coleman wrote:

> 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.

Several people have written me asking which filters we used. I figure  
I'll hit everyone by replying here. I also want to correct an  
incorrect call I sent out with the designs in some of the individual  
replies.

NQ4I uses W3LPL receiving filters that someone built 15-20 years ago  
on the run stations. You can find this design here: http:// 
www.k1ttt.net/technote/w3lplfil.html

These are good filters, and relatively easy to replicate. The filters  
I built for the mult stations are K4VX designs. (I had erroneously  
attributed them to K4VU). I chose this design because it required  
fewer components than the W3LPL design, and appeared easier to tune.  
Both should offer about the same performance. The K4VX design  
appeared in the September 1988 QST, on page 17. This article is  
available at: http://www.arrl.org/tis/info/pdf/8809017.pdf

For my particular reproductions of the K4VX design, I chose to re- 
work the toroids for T37 and T50 cores, which I had on hand.


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