[time-nuts] strange carrier

ed breya eb at telight.com
Sat Nov 15 15:30:57 EST 2014

A signal like that coming from a dish makes some sense to me. I 
vaguely recall from about ten years ago investigating how the 
satellite receivers work, that a fairly strong control signal of 
around 20 kHz was used in some to select the various LNBs and their 
polarizations in more complicated systems. This was passed via the 
cables superimposed on the DC power along with the returning IF 
signals between the set-top box and the dish units.

If the neighbor's setup has a bad connection in a cable end, there 
could be a pretty strong third harmonic of a 20 kHz-ish signal 
leaking out, with a good-sized antenna possibly formed by maybe 
50-100 feet of partly-opened cable shield, depending on the possible 
ground loop paths. Another possibility is if the LNB power line from 
the STB has lots of 20 kHz-ish noise on it from a failure in the local SMPS.

If the possible faults were large, you would think it would be 
noticed as a reception problem by the neighbor, but maybe a partial 
problem is enough for you to see interference. If the interference is 
from the control signal, it would likely be derived from a uP clock, 
so quite stable, while if it's from SMPS switching, it should not be 
very stable, and also loaded with line frequency sidebands.

If that is the case, maybe you could inform the neighbor so that they 
can fix the problem (or you fix it for them), thus improving their 
reception and reliability, and eliminating the interference.

I could be entirely wrong on this, but your last post rang a bell in 
my head as soon as I saw "satellite dish."


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