"Dave Liquorice" writes:

On Sat, 5 Oct 2013 15:57:41 GMT, Windmill wrote:

I saw 12.5 volts going up to the roof, and no change in DC voltage when
things repeatedly stopped working during some rainy gusts.
Later (did I change the channel? Didn't think so, but maybe I must have
done) I saw 19.5 volts, and no more failures although the rain and wind
has died down.

That is normal, the voltage sent to the LNB determines which polarity
signal to receive. The lower being vertical. Curiously I thought the
"acceptable ranges" where 12.5 to 14.5 V and 15.5 to 18 V.

Quite likely it will be 16 when it gets through a demultiplexer then 25
meters of cable then a multiplexer then the motor, before reaching the
LNB.
In fact I had wondered if voltage drop was the cause of the problem,
but that doesn't easily explain the 'works for days / fails every few
minutes' scenario I'm seeing.

Was unhappy to discover when hooking up the Avo that not only does the
cable have just copper-coated-steel inner conductor, ...

Hum, see recent thread about CCS phone cable. It has a significantly
higher resistance than copper, like about 7 times higher. If the
cable is long there could be an appreciable voltage drop across it.
Current is probably 100 mA or more depending on the LNB.
Plus 300 mA if the motor is turning, but of course then the LNB is
less relevant.

... but that the outer braid over the foil can't be soldered because it
is (I think) aluminium braid.

One wouldn't normally solder F-types, they either screw on, crimp or
have a compression fitting.

No, I meant that, so as to get access to the centre conductor, I had
cut in half a short piece of cable with an F connector on one end and a
connector plus F-to-F adaptor on the other, then tried to solder the
two braids together again.
I should have explained properly.
The centre conductors soldered easily, but for the braid I had to use a
little 2 A. terminal block.
It still gave the receiver an adequate signal, though I would not have
been surprised if it hadn't.

Which sounds to me like an accident waiting to happen.

You can't beat copper (well silver probably would but...)

I remember radar stuff which used a lot of silver, and even rhodium.


--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ S c o t s h o m e . c o m
All that is gold does not glister / Not all who wander are lost