Cecil, W5DXP wrote:
"The 180 deg. phase reversing coil is the tricky part."

For UHF, you might prefer to use a 1/4-wave short-circuited stub in
place of a coil to reverse the phase. My 19th edition of the ARRL
Antenna Book shows such an antenna, "the super J-pole on page 16-25. At
other frequencies, this might be called a "Franklin Antenna". It`s a
1/2-wave in-phase with another 1/2-wave, one mounted directly over the
other.

The super J-pole is designed for 144 MHz, but can be scaled for any
frequency with proper mechanical allowances. Gain is about 6 dB over a
1/4-wave whip.

Best regards, Richard Harrison, KB5WZZI

Richard,

I have the 20th edition. Looking at the picture, I would have difficulty
building this into the end of a SMA plug to sit on top of the radio modem.

Regards

David

Richard Harrison wrote:
Cecil, W5DXP wrote:
"The 180 deg. phase reversing coil is the tricky part."

For UHF, you might prefer to use a 1/4-wave short-circuited stub in
place of a coil to reverse the phase. My 19th edition of the ARRL
Antenna Book shows such an antenna, "the super J-pole on page 16-25. At
other frequencies, this might be called a "Franklin Antenna". It`s a
1/2-wave in-phase with another 1/2-wave, one mounted directly over the
other.

The super J-pole is designed for 144 MHz, but can be scaled for any
frequency with proper mechanical allowances. Gain is about 6 dB over a
1/4-wave whip.

Best regards, Richard Harrison, KB5WZZI

Richard Harrison wrote:
Cecil, W5DXP wrote:
"The 180 deg. phase reversing coil is the tricky part."

For UHF, you might prefer to use a 1/4-wave short-circuited stub in
place of a coil to reverse the phase. My 19th edition of the ARRL
Antenna Book shows such an antenna, "the super J-pole on page 16-25. At
other frequencies, this might be called a "Franklin Antenna". It`s a
1/2-wave in-phase with another 1/2-wave, one mounted directly over the
other.

The stub is a good idea and can be mechanically self-supporting at
920 MHz. However, making the bottom section 1/4WL (as Kraus suggests)
instead of 1/2WL would make for a low feedpoint impedance

The super J-pole is designed for 144 MHz, but can be scaled for any
frequency with proper mechanical allowances. Gain is about 6 dB over a
1/4-wave whip.
--
73, Cecil http://www.qsl.net/w5dxp


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"Richard Harrison" wrote in message
...
Cecil, W5DXP wrote:
"The 180 deg. phase reversing coil is the tricky part."

For UHF, you might prefer to use a 1/4-wave short-circuited stub in
place of a coil to reverse the phase. My 19th edition of the ARRL
Antenna Book shows such an antenna, "the super J-pole on page 16-25. At
other frequencies, this might be called a "Franklin Antenna". It`s a
1/2-wave in-phase with another 1/2-wave, one mounted directly over the
other.

The super J-pole is designed for 144 MHz, but can be scaled for any
frequency with proper mechanical allowances. Gain is about 6 dB over a
1/4-wave whip.

Best regards, Richard Harrison, KB5WZZI

Richard

I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave
stub over a ground. is it easy to show where i've missed something?

Jerry

I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto
the end of a SMA plug based on help from you guys. I have some pics of
the construction if anyone is interested in taking a look.
Where is the appropriate place to post these jpg files ?

I am accessing this newsgroup from my email client presently.

I am not sure how I can optimize this yet. My antenna Analyzer is the
MJF unit that only goes to 440MHz.

I have a 1GHz spec analyzer, 1GHz Sig Gen and a Telonic VSWR kit that
goes to 2.5GHz but I think the drive required to the VSWR "Rho-Tector"
needs to be higher than the 10dBm from the sig gen.

Could I optimize the design with this equipment, or maybe would I be
better to use RSSI levels from a receiver placed say 3m away from
Antenna under test ?

If the antenna works I will be very excited as it is very simple to
construct in around 10 minutes and at a cost of around $3 (no counting
labour).

Thanks for any help.

Jerry Martes wrote:
"Richard Harrison" wrote in message
...

Cecil, W5DXP wrote:
"The 180 deg. phase reversing coil is the tricky part."

For UHF, you might prefer to use a 1/4-wave short-circuited stub in
place of a coil to reverse the phase. My 19th edition of the ARRL
Antenna Book shows such an antenna, "the super J-pole on page 16-25. At
other frequencies, this might be called a "Franklin Antenna". It`s a
1/2-wave in-phase with another 1/2-wave, one mounted directly over the
other.

The super J-pole is designed for 144 MHz, but can be scaled for any
frequency with proper mechanical allowances. Gain is about 6 dB over a
1/4-wave whip.

Best regards, Richard Harrison, KB5WZZI


Richard

I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave
stub over a ground. is it easy to show where i've missed something?

Jerry

David wrote:

I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto
the end of a SMA plug based on help from you guys.

How are you matching the very high feedpoint impedance?

I have some pics of
the construction if anyone is interested in taking a look.
Where is the appropriate place to post these jpg files ?

Some of us have web pages from qsl.net for that purpose.
There is also a netnews group for that purpose. I think
it is alt.binaries.
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" wrote in message
...
David wrote:

I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto the
end of a SMA plug based on help from you guys.

How are you matching the very high feedpoint impedance?

I have some pics of the construction if anyone is interested in taking a
look.
Where is the appropriate place to post these jpg files ?

Some of us have web pages from qsl.net for that purpose.
There is also a netnews group for that purpose. I think
it is alt.binaries.
--
73, Cecil http://www.qsl.net/w5dxp


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News==----
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Cecil

He is feeding the 1/2 wave antenna in the center, where the impedance will
be somewhere around 70 ohms. His coax feed line is located within one half
of the antenna and exits the 1/2 wave, center excited, dipole at the "high
impedance" end of the dipole.

David sent me some pictures. The antenna looks quite good.

The effectiveness of the "choke" that attempts to disconnect the dipole
from the feed line may be less than ideal, but it is yet unknown how good
this antenna needs to be.

Jerry

Cecil, Using a 1/4 wave open stub.

Cecil Moore wrote:
David wrote:

I have constructed a 915 MHz 1/2 wave, end fed antenna that fits onto
the end of a SMA plug based on help from you guys.


How are you matching the very high feedpoint impedance?

I have some pics of the construction if anyone is interested in taking
a look.
Where is the appropriate place to post these jpg files ?


Some of us have web pages from qsl.net for that purpose.
There is also a netnews group for that purpose. I think
it is alt.binaries.

Jerry Martes wrote:

I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave
stub over a ground. is it easy to show where i've missed something?


I think it should be more like 3 dB, but hadn't said anything until I
had a chance to model it. The quarter wave stub doesn't radiate
significantly, so it can be ignored. A half wavelength element should
have about 1.5 dB gain over a quarter wave. Two of them would give
another 3 dB if it weren't for mutual coupling, but the mutual coupling
of collinear elements reduces the gain to about 1.5 dB over a single
element. (See for example Fig. 39 on p. 8-35 of the ARRL Antenna Book,
20th Edition; look up Collinear, Gain and directivity in the index of
other editions; or model it with your favorite program.)

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Jerry Martes wrote:

I'd have expected the "gain" to be closer to 4 1/2 db over the 1/4 wave
stub over a ground. is it easy to show where i've missed something?


I think it should be more like 3 dB, but hadn't said anything until I had
a chance to model it. The quarter wave stub doesn't radiate significantly,
so it can be ignored. A half wavelength element should have about 1.5 dB
gain over a quarter wave. Two of them would give another 3 dB if it
weren't for mutual coupling, but the mutual coupling of collinear elements
reduces the gain to about 1.5 dB over a single element. (See for example
Fig. 39 on p. 8-35 of the ARRL Antenna Book, 20th Edition; look up
Collinear, Gain and directivity in the index of other editions; or model
it with your favorite program.)

Roy Lewallen, W7EL

Thanks Roy

Your posts always add alot to my understanding. I appreciate your taking
time to evaluate this antenna and then pass the information on to the group.

Jerry