RE: [Repeater-Builder] Repeater heard on Aviation Channel! HELP

[Tony lelieveld]

Gary may very well be on the right track.  We have a repeater on 146.640 which was being heard by, and keying up, a repeater on 146.680 (input 146.080).  Someone un-authorised had fooled around with the duplexer tuning which resulted in the TX putting 45 Watt into the duplexer but only 3 Watt came out of it.  Checking the output on a Spectrum Analyzer revealed a Christmas tree look-a-like display as the TX had gone spurious due to the weird impedance mismatch.  After retuning the duplexer with a Vector Network Analyzer (I am fortunate enough to have the use of one at work) the problem disappeared and all was well again.   This reminds me of an incident many years ago when Industry Canada (then called DOC) contacted us re a ham 2 meter mobile interfering with aircraft communications.  To make a long story short, the local ham wanted more power out of his transmitter and had physically adjusted the low pass filter (the push and squeeze method) for more output power.  He also defeated the purpose of the filter and all kinds of crap was getting through as well.  His Watt meter showed some more power but since it is essentially a non frequency selective device, it didn’t care what was going through.   Which brings up another story of a tech who could not match a ¼ wave mobile antenna to a transmitter no matter how he cut the whip.  Again the Spec A showed that the TX was badly spurious and the antenna was showing lots of reflected power because of it.  Once the PA was tuned properly so that the spurious signals disappeared, the antenna matched just fine.  Sometimes you have to use the proper test equipment to see what is going on.   73, Tony VE3DWI   From: Repeater-Builder@yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com] On Behalf Of Gary Laforce Sent: July 7, 2005 12:23 To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Repeater heard on Aviation Channel! HELP   I have been reading these post for a couple of days now and seen in the original post that you are loosing 110 watts in the duplexer. Maybe I’m the only one that thanks this may have something to do with the problem.   What is the SWR between the tx side of the duplexer and the PA? What is the SWR between the antenna port and the feed line to the antenna? When was the last time the duplexer tuned and how was it tuned (i.e. by the watt meter method or by a tracking generator and a spectrum analyzer?) What is the rx signal sen thru the duplexer and also what is the rx sen on the antenna port of the rx’er?   You should not be loosing 60% of your power into the duplexer something is wrong there. On a 110 watt repeater you should see around 70-80 watts out of the duplexer at least I have seen a little more.         Just my two cents Gary LaForce N0PBM   size=2 width=500 style='width: 375.0pt' align=left> YAHOO! GROUPS LINKS  Visit your group "Repeater-Builder" on the web.    To unsubscribe from this group, send an email to:  [EMAIL PROTECTED]    Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.