"Arfa Daily" wrote in message
...

"tony sayer" wrote in message
...
I guess you would get it on and off capacitively. Not too difficult to
make
a cap of a few decimals of a uF at several hundred kV working, I would
have
thought. You'd then use these to bridge any high inductances in the way,
such as tranny windings, and to get the data on and off. Depending on the
frequencies involved, you may actually get away with a few hundred pF.

Perhaps but I don't seem to remember seeing much else apart from longish
glass insulators big switch gear and fecking big trannies!...


I'm sure that such caps must have existed when megawatt main UHF TV
transmitter sites, such as Sandy Heath, used valve transmitters at the
bottom of the mast ( perhaps still do ?? ).

Klystons 'tho solid state may be used there now.

Do note that the megawatt etc is radiated power, much more to do with
aerial gains. They don't have megga-watt UHF TV tx'es....


--
Tony Sayer


Yeah, know all about ERPs, but do the flat panel transmission antennas
actually have much gain ? Thought they were just a bunch of co-phased
dipoles. Bet the launch power from the tx is still a good 2 or 300 kW,
though, and I'd bet that there was a fair whack of volts on the klystron
to get there ...

Arfa
The high-power UHF TV Transmitters in the UK are 50kW, mostly PyeTVT/Harris
with a number of Marconi as well. The difference between the Tx power and
ERP is entirely made up of antenna gain. UHF antennas have a very narrow
beam, tilted downwards, as there's no point sending power off into space.
The beam is sufficiently narrow so that the signal close to the mast is
actually less than at a distance, also avoiding people's receivers from
overloading.

I don't know how many Klystrons are left in UK service, I would guess a fair
few. Channel 5 was engineered right from the start with Solid State
transmitters, of , if I remember correctly 10kW power, Channel 4 was
klystron originally.

S.