Date: Fri, 07 Dec 2018 19:21:02 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] High temp magnet wire?
> JI depicts some sky high Z
> numbers, etc, when he tested that choke with his VNA.... on all 9 x
> bands.
<<<Would like to see that. Is it piblished somewhere?
<Manfred
### https://www.w8ji.com/rf_plate_choke.htm Excellent writeup.
Scroll to the bottom to see his VNA results. For choke dissipation
he is using RMS voltage squared / RP. RMS RF voltage = 60% of
loaded B+.
## Note, that graph at the bottom is NOT the currently produced choke that
Ameritron uses... which btw, is the same one sold by RF parts. Its also
the same choke
used in the current crop of alpha amps. The choke depicted in the graph
resonates on
12.1 mhz and 15.7 mhz. The current production choke resonates on 12.5
mhz..and 27.1 mhz.
## The graph at the extreme bottom has been cut off. It was all there a few
years ago.
What would be nice, is a higher current version of his choke, doable, but a
pita. Plan B
might be to use 2 of the ameritron chokes in parallel, which will reduce the
uh in half. But at
least the assy would handle double the dc current. Individual RF and DC
currents would be the
same on each individual choke... at least on paper. But the chokes would have
to be spaced well
apart from each other. They would also require bypass caps at the base of
each choke.
## On a side note, that 45 uh choke my buddy tried on 160m, was wound with
18 gauge wire,
not 22 gauge ! The 18 gauge was later removed, and replaced with 22 gauge
wire, on the same 1” diam,
solid teflon rod. That way, the uh could be increased to 70 uh, using the
smaller gauge wire.
The final config uses 135 uh on a 1 inch diameter solid teflon rod, mounted
vertical. The smaller
70 uh choke, also wound on 1 inch teflon rod, Is L bracketed at right angles
to the top of the bigger
choke. Bypass caps at base of big choke. More bypass caps coming off at the
junction... to the NO / hot side
of a spst vac relay. COM / Cold end of same vac relay bonded to chassis.
Cold side of junction caps has 3 megohms
of resistors, between cold side of junction caps... and chassis. With vac
relay de-energized, cold side of junction caps
are DC grounded. With vac relay coil energized, the cold end of the
junction caps are both DC grounded and rf grounded.
With relay energized, the larger choke is effectively out of the circuit.
Both chokes used on 160m only. 70 uh choke
used on 80-15m.
Jim VE7RF
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