RadioBanter - View Single Post - Dual-Z0 Stubs

Richard Clark · May 11th 09, 09:19 PM posted to rec.radio.amateur.antenna

On Mon, 11 May 2009 02:26:04 -0700 (PDT), wrote:

I should have been more explicit.

I took the "Axial Propagation Factor" (4.372 rad/m) figure which was
given by the HamWaves calculator and multiplied it by the coil length
(155mm) to find the effective electrical length of the coil (38.83
degrees). Then I took cos(38.83)=0.779 as the fall-off in current
across the coil.

Hi Steve,

I don't often drop into this side-thread as the topic had drifted into
a stagnated intellectual backwater.

On this and one prior posting by you:
On Sat, 9 May 2009 13:56:31 -0700 (PDT), wrote:
OK, I tried what you suggested. I put my loading coil midway up a 20ft
vertical wire in the EZNEC model. I reduced the number of turns to
lift the resonant frequency to 5.6MHz.

I note how little Corrum really has to offer when you had to take the
same:
effective electrical length of the coil (38.83 degrees)
and change it (to the same effective electrical length? I think not.)
to fit the same available wire, at the same specific frequency - only
at a different height along the available wire.

By my quick read on the stale crisis of current "fall-off" and proving
Corum by EZNEC; it seems quite apparent that EZNEC (the authority) is
driving the coil requirements which are then force fitted by Corum's
inappropriate application.

After all, Corum says nothing of:
1. Application;
2. Base loading;
3. Mid or Top loading;
4. Stinger selection;
and yet all solutions seem to derive from their math with the elegance
of an ad-hoc "missing degrees" provision (that is quickly discarded as
shown above when current becomes the focus).

Corum DOES say that the formula is only applicable for certain
constraints which I note are NEVER observed in the application nor the
breach. All of the commentary proceeds through equation (32) when
every argument is an instance of equation (31).

How much are you willing to accept of that paper (which is another way
of asking how much you are willing to discard)?

I will ask one ace-buster question that I expect no one will answer:
Show me the computation for M (= tau · a)
which would be appropriate for the NON-quarterwave resonance of the
coil in question at 3.85 MHz.

For extra credit:
1. What is the wave number, k for 3.85 MHz?
2. What is the phase velocity for the original (not changed) coil?
3. What is tau for the original (not changed) coil at 3.85 MHz?

Yes, this is intimidating to ask; but seeing there are so many
authorities on Corum; and that these considerations would have been
done by the authors themselves; then their solutions must reside
somewhere in notes or as marginalia for quick reporting (or could be
summoned up through running through the same math as before).

73's
Richard Clark, KB7QHC