My 2 cents worth.. I use 3 different types of filters plus stubs here. For
the single band stations I use the ICE single band filters between the radio
and amp, on the so2r station I use the model 419 switched filters. On each
band I use the k2tr stubs after the amp. And on the beverages I use the
w3lpl rx filters.
There is an interesting added advantage to the w3lpl filters for m/m
beverage use. I have 6 directions of beverages that all come in to one
switchbox in the shack. That box is a matrix that lets 40/80/160 each
select any 1 of the 6 directions independently. When I first set it up
without bandpass filters there was interaction between the selections, i.e.
if 40m selected the same one as 160m it was ok as long as 40m was actually
listening to it(so the coax from the switch to the radio was terminated by
the rx), but if 40m switched it off (so the coax was open at the radio end)
it reduced the signal on 160m badly (because of the now open ended stub coax
that must have looked like a short circuit at the switch box). The w3lpl
filters have a high input impedance outside of their passband, so by putting
those filters right at the switchbox it not only filters out the other
bands, but decouples the coax from the switchbox so there is no interaction
between bands.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: cq-contest-bounces@contesting.com [mailto:cq-contest-
> bounces@contesting.com] On Behalf Of Bill Coleman
> Sent: Monday, July 18, 2005 12:43
> To: Bill Coleman
> Cc: W1HIJCW@aol.com; CQ-Contest@contesting.com
> Subject: Re: [CQ-Contest] Question re Interstation interference
>
>
> 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@arrl.net
> Quote: "Not within a thousand years will man ever fly!"
> -- Wilbur Wright, 1901
>
> _______________________________________________
> CQ-Contest mailing list
> CQ-Contest@contesting.com
> http://lists.contesting.com/mailman/listinfo/cq-contest
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|