[Nottingham] Wireless interference

Martin martin at ml1.co.uk
Fri Nov 16 20:50:37 UTC 2012

> *Most* consumer HAM gear is not properly grounded and that's where you
> find televisions getting knocked out every time the operator keys up.


Sorry, got to take great exception to that one...

Most if not all radio hams have enough of an interest to know about how
to connect up transmit aerials and how to keep their transmitter and
aerial matched to avoid silliness from a bad standing wave ratio.

You can run transmitters and receivers completely unearthed. You do that
by just using a "handheld" or when using your mobile phone. (Yes, mobile
phones are glorified "walkie-talkie" radio transceivers. Worse still,
they are chirpy radio transceivers...)

The TV problems of olden days were simply super-cheap TV circuits
getting their receivers overloaded by a nearby powerful transmit signal.
The problem there was poor or compromised circuit design in the TV
receiver that had inadequate (or on-existent!) out of band signal
rejection. Hence ANY strong signal, whether from radio hams, the police,
or your local taxi service, would inevitably adversely wobble you
picture. Radio hams did a great service in handing out for free such
tricks as "braid breakers" and "notch filters" to shield those poor
receivers from the real world.

That one has nothing to do with bad earthing.

(Indeed the old TV sets were deliberately NOT earthed and had the
chassis float at mains voltage. The only protection to the aerial, your
video cassette machine, and you, was a few pence few pico Farads
capacitor to block the mains voltage getting out on the coax connector!)

You can have a perfect earth for your equipment. However, that only
helps you to receive the transmitted wideband interference more clearly.
Once the transmissions are radiated into the aether, your aerial and
receiver will pick them up if they are splattering across the radio band
that you're trying to listen to.

Also, telephone wires make for long aerials. They are nominally "twisted
pairs" to limit the problems, but there will still likely be enough
pickup to make ADSL even more of a mess...

Once those PLT/PLE broadband/wideband transmitter things are "out there
in the wild", it will likely be 10 years or more before they are removed
from the scene due to natural causes...

One to watch out for!


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