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? 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.
Dick
-----Original Message-----
From: Rich Measures [SMTP:measures@vc.net]
Sent: Sunday, March 14, 1999 11:49 PM
To: amps@contesting.com
Subject: RE: [AMPS] Chokes and Dipping chokes?
Dick Ehrhorn said...
>Hi Bill...
>
>I agree with both Vic and Carl, but to add a few tidbits: ...snip... 2)
Use a wide strap or braid
>to short the ends of the choke so as not to affect its actual series
>resonant frequencies more than necessary; .......
Rich replied...
? How is placing a wide shorting strap adjacent to the winding not going
to affect anything? Why not dip the choke when it is wired in place, 'au
naturel'? When my Kenwood dipper's pickup coil is adjacent to an
installed hv-rfc, it has no problem spotting resonances.
>:.......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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