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RE: Variable Capacitance and Inductance

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Ed,

>I have, and own a operate a few.  The Navy ARC-5 and its USAAF counterparts
were excellent gear and plenty stable enough for general use.  The infamous
BC-375 was an antiquated transmitter used in almost all US bombers during
the war, although as one guy put it "it was made mainly to be shot down in

:-)  I figured the older radios would not have crystals.  Unlike a true HAM
like you, I don't buy radios for what they can do, I buy them to sell.
There is a huge supply of FM radios and antiquated signal generators being
tossed out by the military and it just happened that all the equipment I
bought had crystals.

>> As I mentioned to Dave P., the inductance used in the oscillators of
>> is far smaller than the inductance used in Tesla's coils.  And most
>> inductances in radio antennas that I know of use ferrite cores, which
>> to stabilize the inductance.  In older radio oscillators most of the
>> oscillator inductance is in the wires between the vacuum tubes, and the
>> oscillations are maintained mostly with RC circuits.

>Incorrect.  For example, I have a Navy RBL receiver built during WW2 (the
design was older) which uses inductors with inductance as high as 50
millihenries and more,

Are these air cores or ferrite core inductors?  If they are ferrite core,
then the inductance will be more stable and less prone to drift.

>> I have 4 old AM tube radios.  The stations come in fine during the day
>> just after the sun sets and just before it rises the radio stations drift
>> considerably.

>As has been pointed out already, that is due to changes in ionospheric
propagation, not frequency drift.

I may be wrong in my understanding of frequency and inductance, but I
thought the two were interrelated?  If a radio station is broadcast at
300MHz and I'm receiving it at 305MHz, then I thought the inductance and
capacitance of the signal would have to change in order for the frequency to
change.  I would like to be corrected on this if you still think I'm wrong.

>I've been a ham for well over half a century and hams operators have told
me many strange stories.  A few of them have even been true, but readily
explained by known laws of nature.

If they are true, I imagine they would be.  Have you heard stories of guys
receiving signals apparently from different times?  This is one of the more
interesting stories I have heard.

> But there is no doubt that the earth's position with respect
> to the sun can alter circuitry such that there are frequency changes.

>You and Tesla appear to be the ONLY ones who have ever observed such
alteration in the circuitry due to solar influences other than direct

I dealt with this in greater detail in a previous post to you.  Direct
heating can easily be proved to be inconsequential to the coil's inductance.
If you live near Central Illinois, I can demonstrate to you a coil
combination that has an inductance swing of from a few millihenries up to
25mH at any given moment.  This is no illusion.  Anybody out there who has a
flat spiral coil and solenoid coil can do this experiment.  It may be that
my combination is more in tune since in this combination I use a solenoid
with three times the wire length of the flat spiral.  Just connect the
bottom wire of the solenoid to the center of the flat spiral and measure the
difference between the two free wires.