I don't have a dip meter, Rich :)
----- Original Message -----
From: "Richard" <2@mail.vcnet.com>
To: "Tom Rauch" <W8JI@contesting.com>; " AMPS" <amps@contesting.com>; "Mike"
<W4EF@dellroy.com>
Sent: Monday, May 13, 2002 6:27 AM
Subject: Re: [Amps] Ameritron AL82 @ 17 meters
> ? A faster method of determining HV-RFC resonance freqs is to unplug the
> amp and sweep the choke in place with a dip-meter.
>
> >> Sounds like a neat trick, Tom, but I am not quite clear on the
> >> connection between the light bulb and the T connector. Is the
> >> lightbulb connected between one leg of the T connector and chassis
> >> ground so that the bulb is lightly coupled to the choke via mutual
> >> coupling, or do you actually connect the top of choke in series
> >> between one leg of the lightbulb and ground?
> >
> >One connection goes directly through the T to the load.
> >
> >The T is ground directly to the chassis as close to the top of the
> >choke as possible.
> >
> >A small low current bulb with wire leads connects between the open
> >port of the T and the top of the choke.
> >
> >Everything else is left in place as close as is reasonably possible,
> >including sheet metal, except all connections between the top of the
> >choke and the rest of the system. Only the lamp (or an impedance
> >meter) connects there.
> >
> >The amp is cold. The tank is set below or above the test frequency
> >range so it does not act like a loosely coupled high-Q "suck-out"
> >trap.
> >
> >You just sweep frequency slowly while keeping power low and any
> >inadequacies in the coke show up as an increase in brightness. If you
> >substitute a resistor for the choke you can get a very rough idea of
> >the impedance, but that isn't really a necessary thing. At series
> >resonances the bulb will glow very very brightly even with low
> >exciter power.
> >
> >Now if you move the tip a screwdriver up and down the choke, you
> >will find a point most sensitive to the tip being near the
> >screwdriver. This is where voltage is highest, and where if you add
> >capacitance or remove turns (to reduce capacitance at the that area)
> >choke series resonant frequency will change the largest amount.
> >
> >The amount of inductance overall change can be quite small, but the
> >removal of the tiniest amount of wire (reducing stray
> >capacitance) can move the resonance quite a bit. That's because the
> >impedance at that point is extremely high, with the choke acting like
> >two high-L low-C back-to-back L-networks. That's what causes the
> >series-resonance, and that's how you can find where to remove turns
> >to park unwanted resonances outside desired frequencies.
> >
> >
> >
> > 73, Tom W8JI
> >W8JI@contesting.com
> >
> >_______________________________________________
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> >Amps@contesting.com
> >http://lists.contesting.com/mailman/listinfo/amps
> >
>
>
> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
> www.vcnet.com/measures.
> end
>
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