[SBE] 950 STL curious problem

[Gary O'Guinn]

Hi Henry:

Have you though about interference in the IF stage of the receiver? 
According to the manual from the Moseley website the IF is:
Dual conversion superheterodyne
1st IF = 70 MHz, 2nd IF = 6.4 MHz
Are there any DTV /  LP Analog stations broadcasting on Channels 4 or 5? 
I'm not sure what might be on 6.4 MHz, but if you could look at a 
spectrum analyzer at the IF frequencies, you might find something. 
Another possibility may be a 2nd or 3rd harmonic intermod coming from 
somewhere.

Also on the Moseley site there is a Tech bulletin on the OCXO. Here is 
the link to the PDF:
http://www.moseleysb.com/mb/service_bulletin/starlink_9003q_service_bulletin_061107.pdf
Probably not the same symptoms but it's worth a look (if you haven't 
already).

Gary O'Guinn
KTUU-TV


A9xw at cs.com wrote:

> 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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