[TowerTalk] Field Day

Chris Hoelzle choelzle at cox.net
Mon Jul 3 14:14:39 EDT 2017

I have done Field Day many times and for many years we just had to endure
cross band interference, noise, clicks and so on

One year, the boss brought a group of filters. 

If I was on 20 meters, I would put the 20 meter filter on my xcvr. The
fellow on 40 meters would put the 40 meter filter on his xcvr.

The difference was amazing.  MUCH less cross band noise.
The threat is that if the operator changes bands he will blow the filter,
but as long as he stays on his given band, it makes it better for all other

Chris Hoelzle 
choelzle at cox.net 
Laguna Niguel, CA 
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
Richard (Rick) Karlquist
Sent: Monday, July 03, 2017 11:03 AM
To: Jim Thomson; towertalk at contesting.com
Subject: Re: [TowerTalk] Field Day

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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