Re: LF: Field Strength Meter - advice needed

[Dave Pick <daveyxm@googlemail.com>]

Chris

Have you tried a can of "freezer" spray to identify where the problem lies? Is it the ferrite aerial or is it the FET amplifier? If you have enough gain then a little negative feedback on the FET stage may help, add some un-decoupled source resistor.

Dave 'YXM

2009/5/3 Chris Osborn <g3xiz@yahoo.co.uk>

LF,

I've just rebuilt PA0SE's field strength meter (LF Experimenters' Handbook),
modified for use on the 500 kHz band.

I've followed the published circuit as near as possible considering available components,
the differences being:
a) I have used a small variable capacitor instead of the published varicaps.
b) I used a JFET 2N3819 in the front end instead of dual gate mosfets.
c) Obviously I now use the MW coil of the ferrite rod instead of the published LW coil.

I have made a decent Helmholtz coil which gives a stable magnetic field yet the
field strength meter's output voltage is very dependent on temperature and can vary up to
30 %.

I would be most grateful for any advice on curing this problem as I've spent hours trying
to correct it.

73 Chris G3XIZ

-- 
G3YXM IO92BK Birmingham UK