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Old March 11th 18, 03:44 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 2,448
Default Paranoia or real effect?

On 11/03/2018 11:07, Brian Gaff wrote:
I was talking to somebody a week or so back who swears their freeview goes
blacky and stutters whenever a plane from Heathrow goes over.
Now in the good old analogue days you could detect aircraft flutter quite
easily, how would you go about it on a digital system. I did not rise to the
bait of suggesting I go around as to be honest there would be little I could
do.

We are after all in a very strong signal area here, and I'd have thought it
most unlikely that a properly installed aerial would have this problem,
which leaves either paranoia or a faulty installation.

Brian

Reflected signals from rapidly moving wind turbine blades cause
cancellation and reinforcement effects that can put deep notches in a
mux. The notch will move rapidly across the mux. This can confuse some
TV sets, but not others. AGC inadequacies perhaps?
The fault is most likely to be seen when the turbine is slightly to one
side of the direct signal path, because in that case the receiving
aerial's forward lobe will include the turbine.
In the case of aeroplane reflections, a horizontally polarised TV
aerial, especially a log periodic, will have a forward lobe that
includes a lot of sky above the transmitter direction. A plane in that
area, if flying fairly low, could well have a surface with the angle of
incidence and reflection such that a strong signal might enter the TV
aerial.
I've never seen the fault though with digital TV, but I saw it lots of
times in the analogue days. Going even further back in time it used to
be a real bugger with BI TV.

Bill
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