[TowerTalk] Field Day

Richard (Rick) Karlquist richard at karlquist.com
Mon Jul 3 14:03:20 EDT 2017

On 7/3/2017 9:13 AM, Jim Thomson wrote:
> From: Grant Saviers <grants2 at pacbell.net>
> We experience lot's of buzz from cw into ssb, need to get as far up the
> band as possible.  Reverse also true.  About the same level of trouble

> Grant KZ1W
> ##  band pass filters, each being 7000-7300, probably are not going to do much good,
> if 2 x xcvrs used on the same band, say 40m cw..and 40m ssb.   Heres a thought though.
> I see ICE and others make band pass filters for the warc bands, like 100 khz wide for 17+12M,
> and only 50 khz wide for 30M band.    If they can make a 50 khz wide band pass filter for 30M
> band, they, or somebody should be able to make any BW  filter you want.    IE:  say 7000-7050,

> Jim  VE7RF

I am extremely skeptical that any off the shelf filter for 30 meters is 
only 50 kHz wide, simply based on the fact that the band is 50 kHz wide.
That is only 1/2%.

It is worth reading "Field Day Filters" (April 1973 QST, page 18).
The authors made a fairly serious attempt at building helical resonator
filters.  Even with this technology, the authors state that the
filters they built are not sufficiently selective to do much good
in terms of separating the phone and CW sub-bands.

A better strategy is to use separate receive antennas (as opposed
to receiving on the transmit antennas).  That gives a lot of flexibility
to combat interference in its own right.  We had a lot of success with
this at K6AO ten years ago.

It also allows receive only filters to be constructed.  Receive only 
filters actually have a chance of separating sub bands because they can 
be allowed to have significant insertion loss and they don't have power 
and voltage handling issues.

Rick N6RK

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