[Tech-Assist] Moseley SL9003Q

[Gregory Muir]

Ah, the dreaded Moseley StarLink!

I recently had an involved skirmish with these units.  Yes, concentrate on 
ascertaining the health of the transmitter first then go from there.

Had a StarLink carrying audio for 3 stations (3 stereo channels).  The 
client called me one day and told me that all three channels were dropping 
in and out.  Checked TX output on the LCD display and it said that 
everything was healthy.  Specified power out, no VSWR.

Went to transmitter site and found receive signal level at -80 dBm.  Checked 
path.  OK.  Started suspecting receiver/feedline/antenna problems.  After 
sweeping line and antenna, had Moseley send a test receiver.  Same problem. 
Went back to studio and put Bird on transmission line.  Nearly all TX power 
was being returned!  Additional investigation revealed a Heliax connector in 
transmission line hidden up in ceiling.of building.  Someone had misaligned 
the connector halves when assembling and broke one of the four center 
contact leaves off causing it to fall between the center contact and the 
shell where it became intermittent over time.

Now, why didn't the Moseley TX LCD display indicate high VSWR?  Called 
Moseley tech services.  The young punkin who answered (note: wear your hip 
waders when talking to this person) told me that they have a circulator in 
the transmitter output circuit and that the VSWR circuitry monitors TX power 
BEFORE the circulator.  Huh?  With a configuration like this one would never 
see any VSWR on this unit.  I am hard pressed to believe what he told me.

In reference to your unit, check receive signal level first.  If greater 
than -70 dBm (-50 to -60 ideal range) then receiver should be hearing the TX 
well.  One note on these units - if the receive signal level is lower, they 
become very sensitive to other STLs operating in the area even if they are 
several channels away from yours.  This appears to be a byproduct of the 
wide bandwidth of the receiver and the use of very high density QAM encoding 
(128Q in the unit I was working with).

As far as the TX is concerned, check output with a Bird!!  Don't trust the 
internal display.  The TX output is supposedly protected with an ALC circuit 
which will cut back the power in the event of a TX output port fault which 
may depress the received signal level to where the receiver is incurring a 
high BER due to poor S/N.  Remember - the wider the receive bandwidth, the 
higher the received noise level..

You do have a clear path, don't you?  How about antenna alignment?  All of 
this will be reflected in the received signal level reading.

It's too bad manufacturers don't bring out the I/Q IF signals anymore for 
connection to a modulation analyzer.  One look at the constellation on the 
display one of  these units will tell volumes about what is happening.

Gregory Muir

Wolfram Engineering, Inc.
Great Falls, MT
406-799-5679