[TowerTalk] Field Day in band problems

[Tim Duffy K3LR]

Hello Jim!

I don't think elaborate filters are needed for this application because of 100 watt Field Day transmitters.

Our very successful (we have won 1A, 2A and 3A in the past) Field Day station had dipoles that were used for 80 and 40 (5/8 wave on 80 meters center fed with open wire to allow SSB or CW
operation as well as 40 or 80 meter operation). Johnson 275 watt Matchboxes add lots of attenuation to the other end of the band. The dipoles were 50 feet above ground on a north south
bearing with 400 ft in-between the tips of each. The nulls of the ends of the dipoles although not significant for working stations (the dipoles are close to the ground and are not
directive) sure help reduce the same band interference.

We had good quality triband beams (aka Bencher Skyhawks). They were 40 ft high and in a north/south line spaced at 550 feet. Most of the time the beams were pointed either west or east so
the in band problems between the tribanders was minimum because of the significant front to side ratio of the tribanders (one tribander was for phone and the other for CW).

We used only Icom IC-765s for the operation. Look at the impressive receiver stats for the IC-765 on the ARRL web site product review section.

The combination of antenna selection and placement, open wire fed dipole systems with high quality tuners and very good receivers made the operation flawless.
At 100 watts there was never a problem running SSB and CW on the same band at the same time. So in-band filters were not needed.

Hope that helps.

73!
Tim K3LR


Jim Brown wrote:

> On Mon, 5 Jul 2004 19:21:46 -0000, Jim Jarvis wrote:
>
> >I don't recall where this thread started, but I think it was someone
> >looking for magic filters for in-band FD applications.
> >
> >None of this will help you IN band.  But I've been able to run ssb & cw at the
> >same time, using 4 el 20's @ 70' spaced by about 400', with no difficulty
> whatever.
>
> Where it started was me asking about narrower filters to suppress IN band
> interference (CW and SSB on Field Day). We are already working with 100 w
> to good dipoles at roughly 400' from each other, some at right angles and
> some parallel. And we are working with some radios that are "better" in terms
> of phase noise and intermod, and some that are worse.
>
> The discussion here has been good. I own several ICE bandpass filters, and
> am aware of comarable filters sold by Dunestar. All of these are bandpass
> filters, broadbanded  to cover an entire ham band. I'm looking for filters that are
> much narrower, more like 50-100 kHz wide. Specifically, I'm trying to learn two
> things.
>
> 1) How much attenuation can I hope to get with practical filters over how
> narrow a bandwidth?
>
> 2)  Where can I find designs for practical filters, suitable filters for sale, or
> both?
>
> Jim K9YC
>
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