[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."
Ed
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