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October 21st 03, 05:24 AM

(Richard Harrison) wrote in message ...
Art Unwin, KB9MZ wrote:
"What other options do I have for increasing Q other than silver plating
of the copper?"

Art has access to yhe 1955 edition of Terman`s "Electronics and Radio
Engineering", I believe. On page 32 Terman writes:
"In designing single-layer coils, the highest Q in proportion to size is
obtained when the length of the winding is somewhat less than the
diameter of the coil."

It appears Art went in the right direction by increasing the coil
diameter to 12 inches from 4 inches. Nonetheless, his coil is 35 inches
long.

If Art doesn`t want to use a high permeability core, and his coil
already has the required inductance, it seems fewer turns on a larger
diameter form would have a higher Q, so the length of the coil can be
less than the diameter of the coil for the same inductance.

I recognise the form factor could be better however the change I made
was a huge improvement which I hope to improve by flattening the pipe
in tape winding form.Aty the moment I have two peaks on top band so I
am not ready to change diameters which will come under consideration
when I advance to a lighter construction.

It is good to space the turns by about the diameter of the conductor, or
slightly less. Insulation can be lossy and tends to rise in loss by the
cube of the frequency, so Terman warns about cotton or enamel covered
wire and insulating material used in coil forms at high frequencies. See
page 35 in his 1955 edition.

The existing coil can be measured for inductance, if it is right, and a
coil calculator or program can be consulted to get a coil with better
proportions.

To tune a circuit, a variable capacitor may maintain a better Q than a
variable inductance, (variometer) but at 160 meters, permeability tuning
of the coil should be practical if the power level isn`t too high.
A couple of points here the variometer is only inefficient when you
have a bucking effect, if designed for use in adding inductance I
would suggest that
it would be superior to the use of a capacitor. When you think more
about it the most efficient way is to use just a normal squeezing
action on the inductance length.
Permiability tuning is to be ruled out since the inductance provides
the means
for triple coupling one of which is moved to satisfy 50 ohm impedance
for all frequencies used. Tho I do not use the top band it presents
more of a challenge
than the other bands used with this antenna and it would appear that
one requirement of an antenna for top band is the use of high power
without having to mess with ground radials !

As an aside I seem to remember reading that form factor can exceed the
1:1 ratio
without to much of a problem !!!!
Regards
Art

Best regards, Richard Harrison, KB5WZI