[TowerTalk] Filters for Field Day

[donovanf at starpower.net]

Hi John,

Filters are  N O T  needed to eliminate interference between multiple Field Day transmitters on the same band.  Antenna design, proper choice of polarization, physical separation between antennas, frequency management, and reasonably good transceivers will eliminate all interference.

I was the guy responsible for designing the 18 HF antennas and the site layout for the 23 (yes twenty three) transmitter 
W3AO Field Day entry this year.  Fifteen of those transmitters were simultaneously active on the HF bands for most of the 24 hour operating period.  Eliminating interference among our 15 HF stations was the primary criteria for designing our site and the antennas.
 
For example, on 20 meters we had four stations on the air simultaneously for most of the 24 hours -- with no interference at all -- on  the following approximate frequencies:
  14025 CW
  14080 RTTY or PSK
  14175 GOTA (SSB)
  14320 SSB

So...   How did we did we eliminate all interference with so many HF transmitters and antennas?

1. We used the full 1000 foot site diameter allowed by the rules.

2. All HF antennas were horizontally polarized.  To obtain the maximum possible isolation between stations, no verticals or inverted V dipoles were used.

3. All HF antennas on the same band were in a straight north-south line, with the largest possible separation between every antenna on the same band.  All Yagis were pointed west, all dipoles were broadside east-west.

For example -- on 20 meters -- our four Yagis were at least 300 feet from each other. The spacing between the SSB and GOTA (SSB) Yagis was 700 feet, and the spacing between the CW and RTTY Yagis was 700 feet.

These concepts can be applied to a much smaller Field Day site.  To operate CW and SSB simultaneously on the same band, use two horizontally polarized antennas (dipoles or Yagis) with the elements in a straight line to minimize coupling.  The spacing should be as large as possible, ideally at least 200 feet.  Use reasonably good transceivers, they don't have to be $10,000 radios.

73
Frank
W3LPL

---- Original message ----
>Date: Thu, 3 Jul 2008 12:49:54 -0500
>From: "John Hudson" <jd_hudson at comcast.net>  
>Subject: [TowerTalk] Filters for Field Day  
>To: <towertalk at contesting.com>
>
>This may be off topic a little but I'm looking for some help
>
> 
>
>Our club operates typically 3A during FD with one dedicated CW station and 2
>phone stations and  running dipoles and this year the clubs A3S.. We are
>looking for some band-pass  filters to help with the interference between
>the CW/Phone stations. We currently have ICE filters but they are cut for
>the complete bands (14.000 - 14.350, etc). Does someone make a inline filter
>that will isolate the phone & CW portions??
>
> 
>
>Looking for hints, tips and suggestions and please contact me off list.
>ko4xj at arrl.net
>
> 
>
> 
>
>73
>
> 
>
>John
>
>KO4XJ
>
>www.w4nja.org
>www.w4nja.org/ko4xj.htm
>
> 
>
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