John Smith wrote:
"In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value----?"

It looks experimental to me.

My ARRL Handbook says that the T match has an advantage in that a pair
of transmission line attachment points equidistant from the center of a
resonant wire has a resistance between them. Therefore it is possible to
choose points which match the line Zo. Problem is the physical distance
between the attachment points probably does not match the line spacing.
The handbook suggests a T match made like a folded dipole with
single-wire extensions at its ends. This looks as if it would require
experimentation.. It seems suited for parallel-wire lines.

The gamma match seems to be similar but an ubbalanced scheme where the
grounded line conductor is attached to the center of the radiator and
the ungrounded conductor is connected to the wire at a distance from the
center of the radiator which results in a low SWR on the transmission
line. A variation treats the gamma match as if it were a shunt tower
feed arangement.

The gamma match becomes a feed loop containing a ground path. The feed
loop is sized to that required for a resistive component which matches
the Zo of the transmission line. The loop inductively couples the
antenna with the transmission line. The loop`s reactance is always
inductive and can be tuned out with a series connected variable
capacitor.

It seems a good cut-and-try project to me. Maybe perfect for Art Unwin.

Best regards, Richard Harrison, KB5WZI

Richard H.:

I had only used a "universal stub" and "L-Network" to match a 1/2 wave end
fed before now. The gamma seems interesting.
Just for my curriosity, I will do a full-wave with a T-Match in the next few
days (seems a 1 wave vertical is best suited for high angle radiation
pattern.) I will keep your analysis in mind, especially at that
time--thanks!

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Harrison" wrote in message
...
John Smith wrote:
"In other words, what set of formulas would give you length, conductor
spacing, gamma capacitor value----?"

It looks experimental to me.

My ARRL Handbook says that the T match has an advantage in that a pair
of transmission line attachment points equidistant from the center of a
resonant wire has a resistance between them. Therefore it is possible to
choose points which match the line Zo. Problem is the physical distance
between the attachment points probably does not match the line spacing.
The handbook suggests a T match made like a folded dipole with
single-wire extensions at its ends. This looks as if it would require
experimentation.. It seems suited for parallel-wire lines.

The gamma match seems to be similar but an ubbalanced scheme where the
grounded line conductor is attached to the center of the radiator and
the ungrounded conductor is connected to the wire at a distance from the
center of the radiator which results in a low SWR on the transmission
line. A variation treats the gamma match as if it were a shunt tower
feed arangement.

The gamma match becomes a feed loop containing a ground path. The feed
loop is sized to that required for a resistive component which matches
the Zo of the transmission line. The loop inductively couples the
antenna with the transmission line. The loop`s reactance is always
inductive and can be tuned out with a series connected variable
capacitor.

It seems a good cut-and-try project to me. Maybe perfect for Art Unwin.

Best regards, Richard Harrison, KB5WZI

John Smith wrote:
Just for my curriosity, I will do a full-wave with a T-Match ...
(seems a 1 wave vertical is best suited for high angle radiation
pattern.)

An *end-fed* one wavelength vertical fed against ground has
a high angle radiation pattern, e.g. 36 deg TOA. A one wavelength
vertical with a T-Match is a center-fed antenna. Such an antenna
has a *low angle* radiation pattern, e.g. 11 deg TOA.
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil:
I stand corrected...

Warm regards,
John

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Cecil Moore" wrote in message
...
John Smith wrote:
Just for my curriosity, I will do a full-wave with a T-Match ...
(seems a 1 wave vertical is best suited for high angle radiation
pattern.)

An *end-fed* one wavelength vertical fed against ground has
a high angle radiation pattern, e.g. 36 deg TOA. A one wavelength
vertical with a T-Match is a center-fed antenna. Such an antenna
has a *low angle* radiation pattern, e.g. 11 deg TOA.
--
73, Cecil http://www.qsl.net/w5dxp

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John Smith wrote:
Cecil: I stand corrected...

John, more like "I stand expanded." I wasn't correcting you.
I was just expanding upon your statement. You were entirely
correct about a one wavelength vertical end-fed against ground.
--
73, Cecil http://www.qsl.net/w5dxp


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John Smith wrote:
"In other words, what set of formulas would give you length, conductor
spacing, hgamma capacitor value---?"

Arnold W.P. King was author of the Antennas section of "Transmission
Lines, Antennas, and Wave Guides", McGraw-Hill, 1945. Wing wrote
"Transmission Lines". Mimno wrote "Wave Guides".

On page 158, King wrote:
"---it is possible to modify the antenna itself in such a way that the
input impedance at its terminals is equal to the characteristic
impedance of the line. The usual arrangement, Hig. 28.3, is to attach
conductors at points CD along the antenna (which are not sufficiently
close to the near zone) and join these to the input terminals at AB. The
accurate calculation of the input impedance at AB of the modified
antenna as a function of the resistance CD and the lengths AC and BD has
not been accomplished."

I wouldn`t hold my breath waiting for accurate formulas, but you are
free to try it yourself. The gamma match is similar to the delta match
and must cope with some of the same problems. This may be a case for
experimentation.

Best regards, Richard Harrison, KB5WZI