[UK-CONTEST] Non Contest Query

[Ian White, G3SEK]

QSL wrote:
>Knowing we have a lot of experience here, may I ask the following please.
>

That raises a very good point: what's the general feeling about topics 
that are not strictly and essentially UK-contest related?

I think such discussions can be OK within reasonable limits, because 
contesting attracts many other kinds of skills and knowledge. For 
example, this list is probably the Internet's *only* pool of knowledge 
about Versatowers.

However, it shouldn't be allowed to get out of hand - and some people 
may definitely want *not* to see such discussions.

Many lists handle this by requesting a simple abbreviation on the 
subject line - in this case it would be "NCC:", standing for "No Contest 
Content". If this is used consistently, we can all keep an eye on the 
percentage of NCC material; and if anyone specifically wants not to read 
it, they can set their browser to filter out that keyword. It isn't a 
perfect system, but it does work well enough.


So this one would be "NCC: thermocouple meters"...

>Does anyone know of an easy way to test whether an RF Ammeter is good or not ?
>ie: That the thermocouple has not burnt out.

A thermocouple RF ammeter consists of a thin wire element that gets hot 
from the RF current, and a thermocouple connected to a sensitive DC 
ammeter. It is almost always the thin wire that burns out, so probably 
all you need is a simple continuity check between the terminals. (To be 
on the safe side, use an electronic ohmmeter that doesn't push much 
current through the thermocouple.)

But even if this particular meter is OK, thermocouple meters are a dying 
technology in very sense. If you start to use this one, you'll probably 
blow it before long... everybody does... and then where would you find a 
replacement?

Instead, think about using a ferrite current transformer into a diode RF 
voltmeter. This is far more robust and repairable. Details are on the 
web page about clip-on RF current meters:
www.ifwtech.co.uk/g3sek/in-prac/clip-on/clip-on.htm
Obviously the ferrite core doesn't always need to be split so it will 
clip on - that's just a convenience feature. Also the terminating 
resistor is *essential* to give a low series impedance in the main line.


-- 
73 from Ian G3SEK