[Lowfer] a thought on coils

Thu, 14 Feb 2002 17:32:55 -0500

John,

Very interesting! I would expect the dual pie windings would do fairly well
by themselves and have almost enough inductance without the ferrite core.
The HV winding on a TV flyback transformer would be similar and is not
influenced that much by the core. It's possible that Walt used the core more
for tuning than to reduce the total number of turns required. There would
certainly be much less magnetic field intensity in his core compared to a
core that is wound over its full length. It could also be that Walt used a
ferrite with a low permeability having a higher saturation value than
commonly used cores.

I like the idea of placing the loading coil close to the top hat. This
maximizes the effective length of the antenna and reduces the effect of the
stray capacity from the vertical portion to the lossy soil.

Bill    

-----Original Message-----
From: john hoopes [mailto:[email protected]]
Sent: Thursday, February 14, 2002 2:15 PM
To: [email protected]
Subject: RE: [Lowfer] a thought on coils

Bill, although I have never personally experimented with ferrite loaded
coils, I have read various articles with the data claims you mention. It
seems pretty discouraging at first, and had it not been for my visit to
Walt's, I would have never given ferrite loaded coils a second thought.

Walt went into some detail about his coil but the only thing I can remember
is that the PI windings were jumble wound. That struck me as rather odd, but
who am I to argue with success. I know Walt was a stickler for efficiency.
He told me "If it isn't efficient, I'll rip it out."

From what I can remember, the coil was enclosed in what appeared to be a 4"
piece of PVC with end caps. Total length seemed to be 4" or so but it was
hard to tell because the coil was mounted at the top of his antenna just
underneath the top hat. I must admit I was a little disappointed at first
because I expected to see a huge coil at the base of his tower. Instead
there was a small aluminum box that housed a matching network from the
transmitter to the low Z of the antenna.

BTW, Walt used a home brew transceiver for both transmitting and receiving
that was a beautiful piece of work. It is too bad that Walt is no longer in
the hobby because his contributions are truly missed.

73
John/AB4MS/JDH

 -----Original Message-----
From: 	[email protected] [mailto:[email protected]]
On Behalf Of Ashlock,William
Sent:	Thursday, February 14, 2002 12:15 PM
To:	'[email protected]'
Subject:	RE: [Lowfer] a thought on coils

Hi John,

>The simplest coil I ever encountered was made by Walt
>Glazar, W3WI. His beacon WI was heard all over the East coast as well as
the
>mid west and it consisted of nothing more than a PVC form with two pi wound
>litz sections over a small ferrite rod. Walt was a stickler for efficiency
>and if it didn't perform, it didn't stay in his beacon. Ferrite is very
>useable if you don't saturate it with too much power provides an easy way
to
>tune a coil to resonance.

I have spent many hours trying to design loading coils using various types
of ferrite cores because they appear to offer reduced size and ease in
construction. The best Q I have been able to obtain is approx 100 at 150ma
of current. Turns out it is very easy to saturate ferrite cores. I have seen
boasts of transmitting performance for these coils from many sources, but
when it comes to the actual coil Q, at the typical 150ma antenna current,
there's always a conspicuous lack of data.

Speaking of simple coils, using Litz on a 4" PVC pipe (preferably with
slots) a Q of >300 is no problem at all. Not sure why the 'bucket brigade'
approach is so popular, except for the lower cost of the house wire. The Rac
for #14 copper wire at 185k is not really that good because of the 'skin
effect' losses.

BTW: Do have or can you get some more details about WI's loading coil?

Bill

*********************************************************************
This footnote confirms that this e-mail message has been scanned for
the presence of known computer viruses by the MessageLabs Virus
Control Centre. However, it is still recommended that you use
local virus scanning software to monitor for the presence of viruses.
*********************************************************************

_______________________________________________
Lowfer mailing list
[email protected]
http://mailman.qth.net/mailman/listinfo/lowfer

_______________________________________________
Lowfer mailing list
[email protected]
http://mailman.qth.net/mailman/listinfo/lowfer

*********************************************************************
This footnote confirms that this e-mail message has been scanned for
the presence of known computer viruses by the MessageLabs Virus 
Control Centre. However, it is still recommended that you use
local virus scanning software to monitor for the presence of viruses.
*********************************************************************