On Thu, 12 Dec 2013 20:15:33 -0000, Chris Hogg <
m...@privacy.net> wrote:
> On Thu, 12 Dec 2013 19:47:20 GMT, The Other John <
nom...@here.org>
> wrote:
>
>> On Thu, 12 Dec 2013 19:12:58 +0000, mogga wrote:
>>
>>> We're getting some new street lights and have noticed they have little
>>> antennas on the top.
>>>
>>> What is it for? They look like they have a light detetctor same as the
>>> old ones too.
>>
>> They are remote controlled and dim-able, we've got them too.
>>
>> TOJ.
>
> We have them here also (West Cornwall). Many years ago, say in the
> early 1960's, the street lights here were switched on from a control
> centre in Redruth. A pulsing audio-frequency signal was sent through
> the mains supply (about 1 pulse per second IIRC), which set a sort of
> balance-wheel arrangement oscillating in the control box in the
> lamp-post, until the amplitude got large enough to close a contact,
> switching on an individual light or short sections of lights. The
> slight variation in characteristics of the oscillating switch meant
> that the lights didn't all come on together, but over a period of a
> few seconds, so reducing the sudden drain on the mains supply, AIUI. I
> used to have a Cossor CR100 communications receiver*, and obviously
> something in the power supply wasn't very well screened, as I could
> always hear when the street lights were being switched on. There was a
> greatly enlarged model of this oscillating switch on display in the
> Science Museum, which worked when you pressed one of the buttons that
> were on every display case.
>
> *
http://www.shopingathome.com/images/B28.jpg
Adding crap to the mains supply is not a good idea, as you found out.
--
Why do the Scots wear kilts?
Sheep can hear a zipper at 500 yds....