On Mon, 15 Mar 1999 11:08:18 -0700 "Richard W. Ehrhorn" <w4eto@rmii.com>
writes:
>
>Did I miss something? How can you inductively couple a dipper to any
>inductor's series resonance without shorting the subject L end-to-end?
Nope you didnt miss a thing Dick...I just kept quiet for once and was
waiting for the groupies to comment.
>Any
>dips you get with the RFC just sitting there, wired into the circuit
>and
>NOT shorted end-to-end, are not the choke's series self-resonance(s)
>but
>(a) those of the choke in series with all the external impedances that
>
>connect it end-to-end (through several paths), or (b) parallel
>resonances
>of the choke and all the extraneous parallel Z's in the circuit.
>
>If you want to know whether your choke is series self-resonant at 21.5
>MHz
>(and therefore will likely either blow up, prevent the amp from tuning
>up
>correctly, or both, on 15m), you have to dip it in situ AND shorted
>out
>end-to-end with as low-L a strap as practical. I've found that if a
>1/4" or
>1/2" wide shorting strap is a couple of choke diameters away from the
>
>winding it has little effect on dip frequencies. Results attained this
>way
>seem to correlate quite well with direct measurements of complex
>impedance
>made with a vector Z meter.
Agreed. I use the 1/4" silver plated strap from an old SB-220 output ckt
as my shorting strap, cut to fit of course. A hunk of wire and clip leads
is pure "amateur" level testing. The difference can be well over a Mhz at
25-30MHz.
73 Carl KM1H
>
>Dick
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