On Wed, 12 Feb 2014 15:05:49 -0800 (PST), W5DXP
wrote:

On Wednesday, February 12, 2014 3:21:49 PM UTC-6, Sal wrote:
I'm at one end of the ham-knowledge scale ...

Sal, what is your technical opinion about the propagation delay through a 72uH 75m mobile Texas Bugcatcher loading coil?

Not big enough.
http://upload.wikimedia.org/wikipedia/en/1/14/Large_antenna_loading_coil.jpg
Hmmm... might not fit on my Subaru.

Good question. I seem to recall that you went though this exercise
about two years ago:
http://forums.qrz.com/showthread.php?336568-Delay-through-a-large-air-core-loading-coil
I don't have any better answers than the bad guesses offered. Did you
ever reach a conclusion or a consensus?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Wednesday, February 12, 2014 9:55:39 PM UTC-6, Jeff Liebermann wrote:
Did you ever reach a conclusion or a consensus?

I reached a conclusion based on the inductance calculator at:

http://hamwaves.com/antennas/inductance.html

When I plug the 75m Texas Bugcatcher loading coil into that calculator, it gives an axial propagation factor of 3.5333 radians per meter. Multiplying by 1.4553 gives a propagation factor of 5.142 degrees per inch. Multiplying by the length of the coil, 6.5", yields an electrical length of 33.4 degrees. At 4 MHz, the propagation delay would be 23.2 ns. Because the loading coil is used in a standing wave antenna, the standing wave phase delay and traveling wave propagation delay are unrelated, i.e. a phase delay measurement will not yield the correct propagation delay or number of degrees occupied by the loading coil during normal transmit operation.

Since the complaint was that hams are not technical enough, I thought I would introduce a technical subject and see what happens.
--
73, Cecil, w5dxp.com

On Thursday, February 13, 2014 7:19:34 AM UTC-6, W5DXP wrote:
On Wednesday, February 12, 2014 9:55:39 PM UTC-6, Jeff Liebermann wrote:

Did you ever reach a conclusion or a consensus?



I reached a conclusion based on the inductance calculator at:



http://hamwaves.com/antennas/inductance.html



When I plug the 75m Texas Bugcatcher loading coil into that calculator, it gives an axial propagation factor of 3.5333 radians per meter. Multiplying by 1.4553 gives a propagation factor of 5.142 degrees per inch. Multiplying by the length of the coil, 6.5", yields an electrical length of 33.4 degrees. At 4 MHz, the propagation delay would be 23.2 ns. Because the loading coil is used in a standing wave antenna, the standing wave phase delay and traveling wave propagation delay are unrelated, i.e. a phase delay measurement will not yield the correct propagation delay or number of degrees occupied by the loading coil during normal transmit operation.



Since the complaint was that hams are not technical enough, I thought I would introduce a technical subject and see what happens.

--

73, Cecil, w5dxp.com

Is this related to the great K3BU-W8JI "current across the coil" debate?
Seems some came to the conclusion that the location of the coil had a
lot to do with whether the current was equal at each end of the coil..
IE: in one exact location it could be equal, but in other locations it
could vary at each end.

I forgot now, it's been so long.. I never really worried about it too
much, because even if it were proven that the current dropped across
the coil, it would not change the design of the antenna.
Just more along the lines of something to know or keep in mind.

On Thursday, February 13, 2014 11:09:51 PM UTC-6, wrote:
Is this related to the great K3BU-W8JI "current across the coil" debate?
Seems some came to the conclusion that the location of the coil had a
lot to do with whether the current was equal at each end of the coil..
IE: in one exact location it could be equal, but in other locations it
could vary at each end.

It is related. I wasn't trying to revive the debate - just trying to pick
Sal's brain for his technical opinion.

The total current in a 75m loading coil, like any other standing wave
antenna, is primarily a function of the superposition of the forward
current and reflected current. The total current is highest when those
two currents are in phase and lowest when those two currents are 180
degrees out of phase. The actual energy decrease in current is minor
compared to the effect of phasing. One can assume zero energy decrease
in the individual forward and reflected currents and still be very close
to the measurements of the actual total current.

Strangely enough, both sides of that argument were half-right and
half-wrong. K3BU's argument that the coil replaced all of the missing
part of the antenna was about half right. W8JI's argument that a
phase shift between the top of the coil and the stinger was responsible
for all of the missing part of the antenna was about half right.
--
73, Cecil, w5dxp.com