[SBE] 950 STL curious problem
garyo at ktuu.com
Mon Jul 20 13:33:36 EDT 2009
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
Also on the Moseley site there is a Tech bulletin on the OCXO. Here is
the link to the PDF:
Probably not the same symptoms but it's worth a look (if you haven't
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
> 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
> 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.
> The SBE Roundtable, SBE at sbe.org
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