From: "G4WGT - Gary" <g4wgt@talkgas.net>
To: rsgb_lf_group@blacksheep.org
Date: Fri, 20 Feb 2004 21:12:54 -0000
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Subject: LF: RE: RE: RF Current meter
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Hi to all at LF,

Thank you for all the replies, tips & advice, some very en-lightening
comments.

I have started very simply by constructing the design shown in the LF
Experimenters Hand Book by Peter G3LDO. It works fine by using a random
(tape recorder VU/Batt) meter from the junk box, its fsd when in a DC test
circuit in series with my digi meter is 300uA & resistance 1.15K so its
indication is not accurate, just an indication that it is reading RF
current.

If (as Alan pointed out the increased volts in the probe with higher RF
current), I were to use a 500uA fsd meter in a design for a 1A fsd RF
current probe would that be linear ie. fsd 5A RF current ? The design by
Lyle (K0LR) seem to suggest so), I will try it of course & see what results
it gives me ! Then I will try to effect some sort of calibration. I have a
500uA meter with 185R marked on the scale (my digi meter confirms this) & 2
other 500uA with a measured resistance of 200R & 350R.

An interesting occurrence when testing the simple RF clip on current meter
on the bench, I used my Marathon 5w Tx to provide RF to test the meter,
separated a small section of the coax inner & shield, fed into 50R dummy
load & got 75% fsd, so I shunted the meter until it just moved off the
bottom of the scale, went to the base of the LF vertical whilst transmitting
with about 100w DC i/p but there was no reading on the meter, I then removed
the shunt & did the same test & got about a 50% fsd reading, I can't work
that one out.

So, learning curves all the time.

73

Gary - G4WGT