[CQ-Contest] Band-pass filters

[Dave Hachadorian]

On Mon, 2 Jul 2001 19:50:06 -0700 (PDT) BILL STRAW <wb0o at yahoo.com>
writes:

> If radio 1 is on 7 mhz, 
> and radio 2 is on 14/21/28 mhz the need to protect
> radio 2 from radio 1 harmonics is obvious, but does
> radio 1 need to be protected from radio 2? Can I just
> be thoughtful and careful (always keeping the
> unprotected radio at a lower frequency) and avoid 
> buying a second set of 160-10 filters?

Hi Bill,

The following info relates to the typical ham installation,
where the antenna are within 200 meters of each other.

You need filters on a synthesized transmitting radio to keep its
wideband noise constrained to that one band. Otherwise, it will wipe
out ALL bands while it is in the transmit mode. This is a loud hiss-type
noise that cannot be filtered out on the receive radio, since it
will be in the receive band. The hiss is present whenever the rig is
in transmit mode, even if the power output is zero.

You need filters on the receive radio to keep out the RF on the
fundamental
frequency of the transmitting radio. This rf amplitude is so high
that it can burn out the front end of the receive radio, even if it is
tuned to a different band.

Since the transmitting and receiving radios are always changing roles,
the bottom line is that you need two sets of filters.

Are you using single band filters? If so, you might consider putting
10/20/80 on one radio and 15/40/160 on the other. That will allow
you to do so2r on any two adjacent bands, which is what you usually
want to do anyway.


Dave Hachadorian, K6LL
Yuma, AZ
K6LL at juno.com


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