In article ,
Geoffrey S. Mendelson wrote:

Do you have the user written manual? It is in German and AFAIK never translated
but a lot of it is pretty obvious anyway. For example the specs to make
your own "grid dip" coils can be figured out, once you understand the metric
wire sizes.

.... but, alas, probably not worth the effort (in my experience, at
least). The MFJ 2x9 with the grid-dip coils is absolutely the least
sensitive and hardest-to-use grid-dip oscillator I've tried.

A few years ago I did a three-way shoot-out between GDOs. The test
tank was a piece of scrap Airdux inductor, with an air-variable
capacitor soldered across the ends.

The MFJ had to have its probe coil shoved right up next to the end of
the coil to get a dip indication. The frequency readout was nice and
precise, but the dip was not terribly deep, and with the probe so
close to the coil I'd be very concerned about the probe "loading" the
tank and pulling it off frequency.

A Heathkit solid-state GDO was rather better, with a sharp dip
available with its probe about a half-inch away from the end of the
inductor.

The best results came from a Measurements 59 GDO - the old firebottle
model with a peanut tube in the sensing head. It got a sharp dip
deflection with the probe 2-3" away from the end of the inductor!
This model is big, clunky, and is probably the gold-standard for GDOs.

I've since picked up a Millen but haven't done a head-to-head
comparison with the others. Based on what I've read, it's probably
somewhere between the Measurements and the Heathkit in sensitivity.

The best approach might be a hybrid... use a good GDO to find the dip
frequency, then hold it near an MFJ 2x9 in frequency-counter mode to
get a precise readout of the frequency. It's a shame there's no
single GDO which has both high sensitivity and a really precise
frequency readout.

Might be a tempting project one of these days... build a lambda-diode
GDO and add a precise frequency counter module to it.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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