Reg Edwards wrote:
Ian, not wishing to be classed amongst the old wives you have very
carefully avoided talking about "power radiated from feedlines". You
have shifted to using clamp-on ammeters.
But people who DO discuss things in such terms are unable to justify
the use of chokes by quantifying the power actually radiated and
setting limits on what power level is acceptable or is not acceptable.
If they can't measure or calculate the power level then they know
nothing about what they are are talking.
Refer to what Lord Kelvin said about measurements.
Can you suggest an acceptable level of amps as measured on a clamp-on
ammeter?
No. Reg knows perfectly well that the RF current is only one part of a
much bigger picture.
An acceptable level is one that:
1. Does NOT make the microphone bite your lips (or does not leave
lasting scars :-)
2. Does NOT cause your transmitter to act up because there's too much RF
current flowing through your station, trying to find "ground"
3. Does NOT cause RFI to your family and neighbours
4. Does NOT cause unpredictable changes in transmitter loading
5. Does NOT lead to unacceptable pickup of interference when you're
trying to receive.
So that "acceptable level" depends entirely on each individual's
particular station layout, how they operate, where they live, what kinds
of consumer electronics the family and neighbours use, how they are
installed... and how much that individual ham cares about getting along
with the family and the neighbours.
Every case is totally individual. That is why every individual needs to
do his own thinking and make his own decisions.
The only "old wives' tale" is that somebody else can do it for you, or
tell you from 5000 miles away what does or doesn't matter.
You don't actually need to measure amps in order to make those
decisions. Basically it's all about simple practical things like the
list above.
Where the RF current meter really helps is if you decide you do have an
RFI problem. Then it lets you *see* how well you're managing to fix it.
Too much of RFI investigation work is like groping in the dark. The RF
current meter is like taking a blindfold off.
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek