
Man analyses cause of bad TV reception, finds his TV is de facto radar - theoneill
http://www.frisnit.com/radar/
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cperciva
He could have saved himself some time by looking at two different channels --
assuming the transmitters were in different locations, this would have given
him two different ellipses which only intersected at a few points.

~~~
pmjordan
In the UK, all channels are typically transmitted from all transmitters (with
some regional programming on some channels) and except for some locations
where there's too much spectrum overlap and some channels are missing. Right
now, they're in transition to digital (DVB-T) so that's probably not quite
true anymore, as some transmitters don't have analog channels anymore.
Transmitters are usually also too far apart to be able to receive a good
enough signal from more than one.

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StrawberryFrog
Google "Canary Wharf TV reception" and you'll see that this is not unusual.
Those buildings really messed up reception.

Is digital TV immune to these analogue problems?

We actually have it worse in the part of North London where I live - we're in
a dip, behind a hill, and don't have line of sight on the digital/freeview
transmitters. Everyone has cable.

~~~
pmjordan
_Is digital TV immune to these analogue problems?_

DVB-T uses QAM, which _is_ susceptible to phase problems. However, given that
the information is digital, a decent tuner stands a much better chance of
filtering out the weaker component. You _definitely_ won't see ghost images:
either your bit-error rate is too high for the built-in redundant coding, or
it isn't. So either you get MPEG decoding errors, or you don't.

~~~
albahk
Digital TV streams have error correction so you are likely to experience
either a normal picture or none at all. When I was growing up, even a slightly
fuzzy ghosted Analog picture was better than no picture at all.

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alex_c
I love the subtle british humour. I wish some of my professors had been like
this.

~~~
immad
"So there it is. My television is now an effective Canary Wharf detecting
radar. Probably the most interesting thing I've seen on TV for a long time."
:)

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Timothee
I didn't like the reddit-style title but really enjoyed the explanation from
that guy.

The explanation and method are actually pretty simple but I just wouldn't have
thought about it.

~~~
socratees
TV is my new radar. Such a nice title. I'm expecting some downmods. :(

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designtofly
The physical phenomenon is called multipath and can become an incredibly
difficult and important problem in many applications (e.g. radar guided
missiles).

<http://en.wikipedia.org/wiki/Multipath>

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lallysingh
Actually, passive radar's getting popular for those who don't want their radar
systems bombed out in the first attack run. Specifically, if you don't want
stealths coming in & bombing out your radar installations, hide sensitive
receivers throughout your city and let the cell towers, tv stations, etc. do
the transmission for you.

Donno anything about the signal analysis part of this, but that's the gist of
what I heard.

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mleonhard
Isn't analog TV transmitted on an FM carrier signal? An FM receiver receiving
two signals of the same frequency should synchronize on one, or possibly
oscillate between the two. So it seems like his antenna is placed exactly
where the two signals are in phase, making them indistinguishable to the
receiver. Maybe he could put the signals out of phase by moving his antenna to
the other end of the roof?

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DougBTX
Now, the next step... adapt his aerial to have minimal gain in the direction
of Canary Wharf!

~~~
pmjordan
Or just upgrade to digital. (DVB-T) The Crystal Palace transmitter even
transmits BBC HD (1080i).

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danw
There is also a handy pub density map of mainland Britain on that site:
<http://www.frisnit.com/pubs/index.html>

~~~
ChristianK
In that he says "If you stand at this
point(<http://maps.google.com/maps?q=51.513412,-0.128170>) you will be in the
centre of a 1km diameter circle containing a staggering 167 pubs!"

Which is probably I enjoyed living about 30 yards from that point so much :)
Coincidentally, my apartment (flat) was directly above a Sam Smiths pub. Happy
days ...

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cabalamat
The punchline's very good: "My television is now an effective Canary Wharf
detecting radar. Probably the most interesting thing I've seen on TV for a
long time."

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bprater
Are our UK friends going digital next year too?

~~~
andyking
Most people already have a digital TV receiver, either via terrestrial
(Freeview) or satellite (Sky). There's also cable in some areas.

The old analogue terrestrial signals are being turned off region-by-region.
Part of the Scottish Borders is already off, with the next switchovers being
in August and November in Wales and "Granada", the anachronistic name for the
TV region roughly covering the North West of England. Everywhere will be
changed over by 2012.

Our system is quite different to that in the US; the four main channels (BBC1,
BBC2, ITV and Channel 4) are carried universally by every transmitter, even on
relays covering tiny villages of a few tens of people. Rather than getting
multiple independent TV stations to change over by a certain date, we just
need to go round each region and upgrade all the transmitters to carry four
digital multiplexes rather than four analogue channels. (Of course, it's more
complicated than this, but that's the gist of what's happening.)

There's a lot of information here:
<http://www.digitaluk.co.uk/when_do_i_switch>

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softbuilder
Why do you need a tv license?

~~~
jodrellblank
To get TV without adverts and programs that don't depend on being popular to
be shown.

Alternately, because the law says you have to have one if you have a device
capable of receiving TV signals (in the UK).

~~~
eru
And Germany, too. And they have a really self-righteous collection agency for
the fees.

