Whilst as Mike says these ferrite RF-current meters are easy to make, a
local friend of mine sells a kit which was originally intended for HF
aerials but after a prod from couple of us was tested and works well at LF.
See is web site at http://g4hup.com/index.html Dave G4HUP has devised a
simple calibration that seems to work.
I have to declare I get no pecunary advantage, though it might be good for a
sticky bun next time we meet for coffee :-))
Alan
G3NYK
----- Original Message -----
From: "Mike Dennison" <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 20, 2015 11:15 AM
Subject: Re: Re[2]: LF: Where to measure antenna current?
Thanks John, yes it does help, much appreciated, but what I am still
unsure of is if my Scopematch, that shows voltage and current
waveforms, is also, on the current waveform, displaying antenna
current? Does it not "do the same job" as a current meter?
Your scope match measures the current in the feeder. This is not the
same as that in the antenna which may be a different impedance -
which is why you need a matching circuit (eg transformer). You can
measure the current at the (relatively) 'cold' end of the loading
coil where it meets the matching unit, so there's no need to deal
with the very high volts on the antenna wire itself. You can also
measure it in the earth lead, but I would not rely on earth current
whilst you still appear to have too much stray RF (see my earlier
posting).
A current meter is easy to build. You don't even need to calbrate it
in the short term as you are unlikely to go anywhere near the legal
max ERP..
73 de Mike, G3XDV
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