[SBE] 950 STL curious problem

[Mike Langner]

>From a similar incident in New Mexico.


Check for a new 900 (yes, there is 900 as well as 800) mHz paging
transmitter nearby, or in the path.

Some of 'em are really dirty, run without external clean-up cavities, and
spew "grunge." After all, many of their operators don't care one whit about
clean signals, they just want power, power, power!

Might or might not be the problem for this one, but has caused similar
problems and symptons elsewhere --

Mike

Mike Langner, CPBE
Albuquerque, NM

  -----Original Message-----
  From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org]On Behalf Of
A9xw at cs.com
  Sent: Monday, July 20, 2009 9:54 AM
  To: sbe at sbe.org
  Subject: [SBE] 950 STL curious problem


  Follow with me, this is wierd.

  Day 1,  14 mile STL path for radio, Moseley Starlink 9003Q with LanLink.
  Signal level  - 77.   Less than expected. Turns out trees in middle of
path.

  Waise receive antenna 50 feet and signal level improves to -73. All nice
and stable.

  2 months later, suddenly signal level drops to -80.  Check coax, (1/2"
Heliax)  couple of bumps.  By pass LanLink box at TX end, gain 2 db.  Bypass
LanLink box at RX  end gain 5 dB.  Back to -73.

  Receive level unstable, jumps from -73 to - 93 and back every few seconds.

  All connections checked, and rechecked.  RX does not work at -93 (below
threshold). Patch in Comprex line.

  Replace 1/2" line with 7/8" line. No improvement in signal level.  -80
with Lan link in, -78 with TX lanlink out, -73 with TX anbd RX Lanlink out
and signal begins jumping again -73, -93.

  OK, Lanlink serves as bandpass filter but only other signals on site are 2
class A FM's.

  Can't find cause of  -73, -93 signal level jumps ( a couple seconds
between levels and fairly regular). No improvement in signal level with
increase in coax, that should have gained about 2 dB since 1/2" had 4 dB of
loss) (260').

  Antennas check good. (Scala grid type)

  Only other signal is 950 STL at 90 degrees and distant channel.  Rotating
antenna shows typical and smooth lobes and is dead on.

  Called Moseley, tech says he would bet his house it is not receiver.

  Any guesses other than LGM?  Nothing within 2.5 miles of RX site,  path is
clear and not near intersecting anything else.

  Henry

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