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MFJ products
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 I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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