[EMAIL PROTECTED] wrote:
In a message dated 2/23/2007 4:32:54 P.M. Pacific Standard Time,
[EMAIL PROTECTED] writes:
as all better repeaters builders know, the equipment might have to
be tuned as a system using custom cabling lengths or Z Matchers
for optimal performance.
Can you comment on a difference of opinion regarding how a Z matcher
should be adjusted? One school tunes for maximum smoke downstream of
the cavities which is the approach I adopt. The other school tunes for
minimum reflected SWR between the first cavity and the TX. My academic
preference is for the latter, but as a practical matter it's a pain in
the buns to do because you have to account for the line section that
the Bird meter adds to the cable. Beyond that, using just a meter,
what is it that is actually being measured since it could possibly be
a composite of both on-channel energy and and off-channel reflected
spurs and harmonics.
I think you answered your own question, however I'll bite....
In *most* of the instances where I employed impedance matching between
the transmitter and first cavity, the place where best return loss and
least insertion loss was found, is very close to one another -tuning
wise. I usually use the maximum smoke approach first and see what I
have, then go from there. In my most critical applications, I use
permanent in-line Bird samplers. Then, cabling lengths don't change
because I don't remove the samplers; and you know exactly what you have
and where....
Kevin
