[RFI] IN-band Filters

Tim Duffy K3LR k3lr at k3lr.com
Tue Nov 7 18:23:36 EST 2006

Hi Bryan!

You will find this a tall order.

When I was doing competitive Field Days I found that taking advantage of separation of stations and polarization diversity will provide all the isolation you need. You also need to use radios with great front ends and narrow roofing filters. You should have no problems running 100 watts with two stations on a band (CW and Phone). We had overall high scores in 3A
and 2A using these ideas!

Tim K3LR

Bryan Swadener wrote:

> Hello,
>   I'm looking for some form of filter for the purpose of reducing interference between stations operating on the same band (ie, fone-cw).  This would be used in a planned multi-transmitter contest setup during Field Day 2007.  The bandwidth and slope would need to be good enough to prevent fundamental overload of (and possibly damage to) the receiving station.
>   It appears that, unless I go with very large coaxial cable (in the form of a stub) to attain a high-enough Q, I will need to look at multiple-section lumped-element filters.  I've perused the various commercial filter manufacturers' offerings.  However, all they seem to offer are filters that will pass the entire band.
>   I've install Jim Tonne's "Elsie" and "SVC Filter" software and have managed to come up with a few designs for 40m.  However, though filter design isn't my strong suit, it appears the capacitor values are pretty extreme (< 10pF and > 0.025uF)... and the slope doesn't appear to be all that good.
>   I'm pretty persistent but, before I spend any more effort on this, can a knowledgeable person tell me if I'm just chasing windmills?  Any tips are most appreciated!
>   Vy 73,
>   Bryan WA7PRC
>   bswadener-at-yahoo-dot-com
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