[SMCARA] Repeater Update

[Clarke, Tom AIR4.0P NATOPS]

Pete and I visited the repeater site to do a bit of troubleshooting.  

First check was to put the TDR (Time Domain Reflectometer) on the antenna.  Surprise, big discontinuity (70 ohms up the line) about 6 feet up the feed line.  Let see, the PolyPhaser surge protector is right about there.  Removed it from the line and now a nice 50 ohm line all the way (120feet or so) up the tower to the Super Stationmaster antenna with all elements showing on the scope!  This impedance discontinuity could result in detuning the duplexer cavities .

Problem still there.

Fired up the H-P signal generator and ran it into the receiver, via the duplexer.  Holy Moley, it took at least 3 microvolts to open the squelch.  Deaf!  

Bypassed the duplexer and went straight into the receiver.  Still took nearly 3 microvolts! About a db. or a half db. loss in the duplexer is OK, so the receiver is the culprit.

FYI, an OK receiver will have a half microvolt sensitivity, better is a 1/4 microvolt, and a hot one will have a tenth of a microvolt.  We are nowhere near good enough.

Plan of attack: New channel elements have been ordered for the backup repeater.  This will take a couple of weeks.

Does anyone happen to have a GE MASTR II VHF receiver strip sitting around in their junk box?  We could tune that up and not have to replace the entire machine.

Sorry, no quick fix at the moment.

Keep the faith.

73 Tom/W4OKW

P.S., I had a box of GE stuff at the Tailgate Fest last year and I don't remember who got it.  It may have a receiver in there.  Take a look it you were the lucky recipient of the GE stuff!
TC



Tom Clarke
P-3/C-130 Program Support, PEO(A)
USN/USMC National Airworthiness Office
Naval Air Systems Command, AIR-4.0P
(301) 995-3793/DSN 995-3793
Fax: (301) 342-3276
Cell (301) 904-2053
frederic.clarke at navy.mil

 "We're out of money, now we've got to think."
-- Winston Churchill