Re: pptp-based vpn
On Wed, 12 Aug 2015 08:04:37 -0500
<martin.m@suddenlink.net> wrote:
> Several years ago, one of the United States television
> networks did a story on the British TV license and showed agents
> in a van driving around looking for the tell-tale weak radio
> signals from the local oscillators of television tuners and then
> counting and matching the number of such signals with the number
> of residents in houses to see if anybody had an un-licensed
> television.
>
The story started in the early 20th century, when many designs of radio
receiver cause significant radiation, particularly super-regenerative
types. Poorly designed transmitters might also radiate on frequencies
other than those intended.
The Post Office were given the job of policing radio interference, and a
licence was required for both transmitters and receivers to fund this
activity. They had mobile equipment to track sources of interference.
When the BBC began regular transmission (they were pretty much
hobbyists before that), a decision was made to fund it from increased
receiver licences. The Post Office still issued the licences, and
passed on about 90% (in the 1970s, at least) to the BBC. The
interference-tracking equipment could certainly spot a typical
television receiver, though probably not a properly-designed radio
receiver.
As TV design improved, it became more difficult to detect the local
oscillator, but the horizontal timebase radiated quite powerfully at
low frequencies. In the 70s and 80s, if I needed an atomic frequency
reference to adjust something, I would hang an oscilloscope probe over
the front of a TV and compare the waveform with what I was working on.
So it was until non-CRT television displays became widespread. The
high-power timebase disappeared, and there was pretty much always
standards conversion going on, with a frame or two of storage. Even
when it was possible to detect screen emissions, they were not related
to the transmitted signal, and there was therefore no evidence of use
of a TV tuner. Early personal computers used the television standards
as real computer monitors were enormously expensive, which also
confused detection.
Nobody believes in the existence of detector vans today, but they
certainly existed once. As Lisi said, it is simply assumed that every
pile of bricks everywhere contains at least one TV, and you are very
nearly legally required to somehow prove the absence of one to avoid
prosecution.
--
Joe
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