Hi J, ouch, that is bad news in one way but good news in another. You dont
say what type of meter it was but if thermo suggests that there was very
little current in the antenna. I suspect that it must have been a torroidal
current transformer type otherwise you would not have had any reports. So
what failed the meter or the diodes?
Toroid splitting seems a lot of effort when you can use an "EMC" split core
for the transducer quickly and without a lot of effort. Remember the
reported effect I mentioned (I have no experience of this personally) that
ferrite transformer rf ammeters can give strange readings if mounted within
the field of the loading coil. I dont think size is too important in this
application, because I have used Tek passive current probles for measuring 8
or 9 amps of 136kHz RF during experiments on the bench.
A note on the antenna loading coil. The bifilar link is overkill (only
really necessary to get the widest bandwidth at the highest frequency....not
necessary for a narrow band match) and restricting the match. You might be
better to try an ad hoc overwind maybe of some extra turns on the input side
to see if the match can be improved when you have a replacemnt RF current
meter. If you can crack this you should not need the ferrite transformer
which will be giving some extra loss.
Good Luck
Alan G3NYK
----- Original Message -----
From: J. Allen <[email protected]>
To: LF (RSGB) <[email protected]>
Sent: 18 July 2006 03:05
Subject: LF: RF Ammeter
> Scott and Friends,
>
> The ammeter check results are in.... Dead Meter.
>
> I went over the antenna connections cleaning and soldering and a small
> amount of retuning was required.
>
> Someone asked how things are set up now...
>
> There are two coil forms involved. On the first is a bifilar winding with
> ten turns each for the coaxial feed and for the antenna feed. One end of
> each of these windings is grounded.
>
> The second form has the loading inductor for the antenna. It consists of
a
> single layer close wound solenoid with 40 turns of ~16 Formvar coated wire
> two inches long and 10-3/4 inches in diameter. The entire coil exactly
> resonates the antenna, without taps and without using the Variometer.
>
> It is a very simple and straightforward setup. The fact that there should
> be a lower antenna resistance bothers me, but NOT enough to play with it.
> That antenna plays. I may make up an antenna current meter from the LF
> Today book. What cuts the toroid core material and leaves a sooth cut or
am
> I dreaming?
>
> J.
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