John,
Assuming that the output of the repeater and amp are clean.
This would be my suggestions do this in order to avoid spending any more
than needed.
1) Verify clean output from TX and amp.
2) Verify tuning on the duplexer.
Both of these are most likely fine.
3) Replace all interconnect cables with ¼ of ½ superflex
4) Add circulator to the output of Amp (dual at least maybe even a
triple)
5) Replace duplexer with something from this century.
I read the post about the spur from adding a cavity to the tx output . the
only way that should happed is if there is a problem in the amp in the 1st
place.
Any RF that makes it back through the transmit side of the duplexer can mix
with your frequency and anything else that can get in there. An isolator is
like an RF diode with a drain.
Anything that comes toward your amp from the outside will be diverted into
a dummy load (drain) to be burned off as heat.
You did not say what frequency that you are operating on but how close in
frequency are the nearest repeaters ?
And example if is you are on 464.025 and there is another repeater on
464.050 then your duplexer no matter how good offers no protection itself
that would be the isolators job.
I hope this was helpful and while yes I do have some stuff available my post
is to be helpful not sell stuff.
Regards,
Robert Mitchell
From: [email protected]
[mailto:[EMAIL PROTECTED] On Behalf Of John Transue
Sent: Wednesday, August 20, 2008 11:37 AM
To: [email protected]
Subject: RE: [Repeater-Builder] De-Sense and Circulator Question
First a big thank you to Eric, David, Rodney, and Robert. It seems clear now
that a circulator is not what I need. I plan to re-tune a pass cavity and
put it on the TX side as suggested by Eric. David has warned of the
possibility that this can cause a spur that might interfere with another
system so I will try to have a spectrum analyzer look at the output.
Robert asked for some additional information. Here it is:
RG-400 (new) in the cabinet, RG-214 (new) to the Heliax feed line.
The RF environment is intense. I do not know what all is transmitting, but
there are numerous antennas within 100 feet.
The repeater is a Yaesu Musen FTR-5410. It drives a Mirage PA to about 90
watts.
John Transue
-----Original Message-----
From: [email protected]
[mailto:[EMAIL PROTECTED] On Behalf Of KD4PBC
Sent: Wednesday, August 20, 2008 7:50 AM
To: [email protected]
Subject: RE: [Repeater-Builder] De-Sense and Circulator Question
John,
A couple questions.
What are you using for interconnect cables, antenna, feedline ?
Tell us something about the RF environment Hostile or not ?
What type of radio are you using ?
That Motorola duplexer is a very poor duplexer. With all the holes in them
after a few years they may generate more noise than the suppress.
All interconnecting cables need to be superflex or some other solid shielded
cable.
Any RG type cable the braided shield becomes illuminated and will cause
noise and if there is a non linear junction can produce intermod.
Send me the details and I will try and make some suggestions.
Robert / KD4PBC
