[BC] soldering

[Clive Warner]

> My most common job would be
> silver soldering one-inch or wider, one-eighth copper strap, on to
> galvanised steel angle.

RF asked:
<"How exactly was that done?  Structural engineers and insurance companies
<usually prohibit any kind of modification or process with respect to tower
<members."

- I'm talking, here, about items such as RF ATU cabinets and structures
around the mast or in an ATU that require solid earths. For instance my
Gambia installation had two alloy combiner/rejector cabs mounted on a frame
of 1.5"x1.5" galvanised steel angle section. I ran copper strap to the angle
and across to the other side, and silver soldered it, then coated with
bitumen. This strap was then soldered to the main earth strap.

If you would like to see a photo I will put a couple on my Web site for you.
I haven't done that yet because I am busy writing an account of my year in
Gambia, including photos, and it all takes time. But, if you like, I'll
upload the photos and post the URL here.

I will add one thing:
NEVER use a ring earth in an RF environment. Always use star-point earthing.
I made this mistake once. Never again.
I installed a two inch copper strap right around the inner wall of an ATU
hut adjacent to a driven tower carrying 200KW.
I terminated both ends of the strap at the feeder entry point thinking that
I was doing a great job.
When I powered up both 100's in parallel, after a few minutes I saw a cloud
of smoke coming from the ATU hut. I powered off but it was already too late,
the RF heating (shorted turn effect - massive eddy currents) had set fire to
the aluminium parts of the 4" coax terminations, causing a fire so intense
that the entire termination was destroyed, requiring half a day of work to
repair the wall and re-pull and re-terminate the feeder. (Just as well I had
left a spare loop in case of 'accidents').
- Clive