LF: Re: Measurement of antenna current

["Andrew Talbot" <G4JNT@thersgb.net>]

I would have thought the stray capacitance associated with the ammeter when
measuring current at the top of the coil would cause more than enough
detuning to reduce the current by this much.

But there could still be a slight variation due to the effect you describe.
Wouldn't you be better tapping up from the bottom or using a variometer than
tapping down from the top ?

Andy  G4JNT


-----Original Message-----
From: Steve Rawlings <steve@alg.demon.co.uk>
To: LF Group <rsgb_lf_group@blacksheep.org>
Date: 06 May 2001 22:11
Subject: LF: Measurement of antenna current


> Hi All,
>
> Today, I made some more antenna current measurements on my 12 m
> vertical (and my shiny new loading coil), using a thermocouple
> meter.
>
> At resonance, the current into the base of the loading coil, was
> 2.2 A.  But when measuring the current into the antenna at the
> hot end of the coil, the meter only indicated 1.8 A.  I had
> expected the reading to be the same at both ends of the coil.
>
> The loading coil has many more turns than is required to resonate
> the 12 m vertical, so the connection to the antenna uses a tap
> which is several turns down from the top of the coil.  I've been
> thinking that the excess turns at the top of the coil may be
> causing the difference in current readings.  (This may sound
> silly, but in my mind's eye, I can sort of picture some of the
> current in the coil going into the capacitance of the antenna;
> and some current going into the capacitance of the unused turns.)
>
> Before I try removing the excess turns, I'd like to know whether
> the current should indeed be the same at both ends of the loading
> coil.  Can anyone help?
>
> Regards to all,
> Steve GW4ALG