If the load, antenna, were not 50 Ohm resistive and connecting it caused
the duplexer to become untuned then tuning it with the load would make
very much RF since. Tuning it with a dummy load is only done to insure
a good load, but is not tuning for the real situation.
However, in this case the proper solution would be to fix the antenna
problem, not the duplexer.
73, ron, n9ee/r
Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.
On Fri, May 9, 2008 at 11:55 PM, Nate Duehr wrote:
On May 9, 2008, at 2:54 PM, [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]> wrote:
At 5/9/2008 13:40, you wrote:
if you are using the same wires from the cans to the tees, about all
I can suggest is maybe retuning the duplexers while connected to the
antenna.
If there is 0 dB of desense looking into a dummy load & 30 dB into an
antenna, duplexer retuning is not the answer. The problem is
definitely beyond the duplexer (feedline, antenna, something acting as
a mixer in the near field, etc.)
Also check and recheck each section of cable between the cans,
etc... Not saying this will be the answer, but at this point you
seem to have little to lose by trying it.
..except having to retune the duplexer after you detune it looking for
the real problem. BTDT.
Agreed. Retuning the duplexer "while connected to the antenna" is
what I like to call "voodoo engineering" . In other words, while it
might make you feel better, it has no basis in RF engineering reality.
Wave a dead chicken over the repeater while you're at it. It'll do as
much good. :-)
How do you tune a duplexer properly? One can at a time.
If you hook it together and test it properly terminated, and it needs
retuning, what's wrong? Cable lengths.
If you hook it to your antenna system and it somehow magically goes
out of tune? Something else is (badly) wrong. Probably an antenna
system that doesn't present a 50 ohm (or anything close to it) load.
The way I was taught, and the way I teach is: They put those lock
nuts on the duplexer for a reason. Use 'em. (In other words, leave
the duplexer alone. Tune it and forget about it.)
I've yet to see a quarter wave stub in a can with a lock/jam nut
tightened properly (a duplexer), go "out of tune"... no matter how
many years went by since the last time it was checked.
--
Nate Duehr, WY0X
[EMAIL PROTECTED] com <mailto:[EMAIL PROTECTED]>
<mailto:[EMAIL PROTECTED]>
