The key problem is dirty transmitters, as opposed to receiver
overload. You can afford an extra 6 or 10 dB of receiver front end loss
due to filtering to fix receiver overload. On the transmit side,
any significant loss produces a lot of heat, plus you need extra
transmitter power to make up for the loss. Before resorting to
this, it is better to set up separate receive antennas adjusted
to null the transmit antenna with directivity and/or cross polarization.
Typically, the best unloaded Q is around 1000, which means that
you lose 1 dB per resonator if the separation is 10% (rough
rule of thumb). A tunable notch at the receive frequency in the
transmitter feed line gives best rejection vs loss. The problem
is that station A needs to control station B's notch by remote
control, and vice versa.
40 years ago, using vacuum tube equipment, and no filters, we
somehow managed to operate on phone and cw in the same band
at the same time on field day with antennas 100 feet apart.
Rick N6RK
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Jim Brown
> Sent: Saturday, July 03, 2004 8:27 PM
> To: Tower Talk List
> Subject: [TowerTalk] Narrow Band Filters
>
>
> I'm thinking about building some narrow band filters (as opposed
> to a bandpass filter that
> covers an entire band) for use on Field Day. The object is to
> minimize crosstalk between CW
> and sideband stations on the same band. Has anyone tried this?
> Is it practical to get enough Q
> to pick up enough rejection to make it worth the trouble?
> Certainly 80/75 would be the most
> practical, since it is the greatest percentage bandwidth. Is
> anyone making a commercial
> product?
>
> Jim K9YC
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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