[Milsurplus] BC-230 questions and observation

[Hue Miller]

Thanks Ken for your input on the BC-230 output circuit. 
I guess i still do not totally understand the action of the loading
when dealing with reactive load. If the load is purely resistive,
like a 1/4 or 1/2 wave antenna, i can see that the coil tap
acts simply as an impedance transformer from the low tens
ohms, near the bottom of the coil, or in the few thousands ohms,
nearer the top of the coil. 
However, here's where i have a problem. The short aircraft 
antenna ( or car whip, or any short antenna ) is modeled as
a low resistance, 10 ohms or less, in series with a capacity of
something like 50-100 pF. The "phantom antenna" boxes all
have some circuit like this in them. So on a BC-230 type 
circuit, where approximately does the tap go to load such
an antenna? In the ARC-5 transmitter, i can understand the
roller coil inductance resonates with the antenna capacity
to cancel out this series capacitve reactance, then the low
pure resistance of the antenna deals with the low impedance
winding over the plate tank circuit. But the -230 has no 
series loading coil. I know from playing with crystal radios
that the random wire antenna, which is short at BC wave-
lengths, can go right to the top of the coil, because the 
antenna's high impedance (considering the capacitive
reactance) is an approximate match to the tuned circuit's
high impedance.  So on the -230, to match a short wire
antenna, as on a trainer single-place plane, the tap would
be very high on the coil? I tend to think so, from the above,
and also from the schematic for the Army SCR-583/ 
BC-1209 trans/receiver  ( like a BC-654 except 2.2-4.6
and a little older ), the short mobile whip antenna goes 
right to the top of the tank circuit! That means like not
very good harmonic suppression.

I do have an ulterior motive in these inquiries, besides 
me learning about how this circuit works. I refer to
the claims of one interest group that they have evidence
that SOS messages from Amelia Earhart were heard
in the USA on harmonics of AE's aircraft transmitter.
This group is TIGHAR, The International Group for
Historic Aircraft Recovery. I am actually a member
but i am on the warpath against claims of theirs i think
are clearly silly or supported by illogic. They have a
so-called analysis of whether those receptions were
possible at

http://www.tighar.org/Projects/Earhart/Bulletins/03_15_01Bulletin/03_15_01bulletin.html

I recently wrote them a long post pointing out that 
their understanding of the transmitter was basically 
wrong and their assumptions of harmonic output
power were just that, unsubstantiated assumptions.
Also i think the writer of that report abuses the 
propagation prediction tools, but i simply do not
have the learning & exeperience to refute that.
I can email this to anyone who is interested.
Then there is the fact that of all the USA, with 4-6
shortwave hobby magazines and thousands of SWLs
taking part in this technical hobby of the time, 1937,
we have: 1 boy, 2 girls, and 1 woman reporting 
hearing Earhart. Sounds like a vision of the Virgin
Mary in the reflections of a glass window, to me.

The WECo. transmitter AE had on board uses the
same kind of tapped coil output as the BC-230. 
It seems to me the worst case, in terms of harmonic
output, would be when the antenna is end fed 1/2
wave, high impedance, then the coil tap is high,
and for the odd harmonics, the coil tap is far enuff
away from ground to permit more harmonic to 
exit. The question for me, is what happens when the
antenna is more like the typical short aircraft antenna.
Jack Antonio did some great work recently with a 
spectrum analyzer and the BC-230. His results 
were for a low impedance antenna and show at
least 30 db down for any harmonic, very gradually
falling off as you go up. I believe his work was very
carefully done but i am surprised the harmonics
were this far down. I would GREATLY appreciate
input from anyone on the harmonic issue from such
simple tapped-coil output circuits - but the kind of
input i need is fact, numbers, not opinions on whether
the TIGHAR claim is true/false. I am thinking i will
post this inquiry to GB, Boatanchors, and even
Kurt N. Sterba. I am on the warpath - i have had it
with nonsense claims and dogmatic clinging to the  
party line - you don't know the half of it. If  i am 
wrong, so be it, but i want that conclusion based on
fact, not belief.
Thanks- Hue Miller  KA7LXY