On Fri, 25 Sep 2015 10:49:10 +0100, Mark Carver
wrote:

On 25/09/2015 10:23, wrote:
In uk.d-i-y Mark Carver wrote:
On 25/09/2015 09:20, Big Les Wade wrote:

You seem to be saying here that interference from planes can't happen
because it would cause too much fuss from householders. Yet above, you
say "Yes, 'aeroplane flutter' was an issue in the analogue days"? Which
is it; interference from planes can happen, or it can't? Why would
householder fussing prevent interference to the digital signal but not
to the analogue signal?

Because of the way COFDM modulation (used for digital TV and DAB) works,
you effectively have interleaved data (with forward error correction),
spread over a few thousand separate carriers occupying almost 8 MHz (for
TV) of spectrum. Any reflection (at any given moment) will only cancel a
small selection of those carriers.

We have a boat moored at Gallions Point Marina, right under the flight
path into London City Airport. OK, we *are* very close to the
aircraft when they land but they certainly do break up the signal
(both vision and sound) on our Freeview TV. It's not just a minor
hiccough either, the sound goes off and the picture breaks up and
freezes for the few seconds while an aeroplane goes over. It is only
a few seconds though.

Yes, that doesn't surprise me, a plane very low will be reflecting
enough stuff back with a large aperture to 'punch out' enough of a mux
for a few seconds as it passes over.

As ever with all digital reception issues the only viable method to
see what's going on is with a spectrum analyser.

Mr Wright of both these parishes has published work on the effect
on reception of windfarms, which is a related subject of course.

http://www.wrightsaerials.tv/services/interference-studies/television_interference_studies_for_wind_turbine_i nstallations.pdf

That's our Bill ameliorating in public again.

--

Graham.

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