On Thursday, June 6, 2013 8:34:04 AM UTC-5, Geoffrey S. Mendelson wrote:
What do I have?

http://en.wikipedia.org/wiki/Folded_unipole_antenna
--
73, Cecil, w5dxp.com

In message ,
W5DXP writes
On Thursday, June 6, 2013 8:34:04 AM UTC-5, Geoffrey S. Mendelson wrote:
What do I have?

http://en.wikipedia.org/wiki/Folded_unipole_antenna
--
73, Cecil, w5dxp.com

I think what Geoff is describing is not the usual folded unipole (twin
feeder shorted at the top, and at the bottom, one side fed from the TX,
and the other side grounded and/or connected to radials), but rather
twin feeder where the top end is shorted, and at the bottom, one side is
fed from the TX, and the other side is open circuit.
--
Ian

On Friday, June 7, 2013 4:42:13 PM UTC-5, Ian Jackson wrote:
... one side is fed from the TX, and the other side is open circuit.

The 1/4WL folded monopole is resonant with a feedpoint impedance around three times a 1/4WL single-wire monopole. Those two antennas have approximately the same gain.

If one disconnects the folded element's ground connection leaving an open-circuit, the feedpoint reactance becomes extremely high and the antenna loses about 6dB of gain compared to the standard 1/4WL monopole. It looks more like a 1/4WL shorted stub than an antenna.

In message ,
W5DXP writes
On Friday, June 7, 2013 4:42:13 PM UTC-5, Ian Jackson wrote:
... one side is fed from the TX, and the other side is open circuit.

The 1/4WL folded monopole is resonant with a feedpoint impedance around
three times a 1/4WL single-wire monopole. Those two antennas have
approximately the same gain.

If one disconnects the folded element's ground connection leaving an
open-circuit, the feedpoint reactance becomes extremely high and the
antenna loses about 6dB of gain compared to the standard 1/4WL
monopole. It looks more like a 1/4WL shorted stub than an antenna.

I thought something like that would happen. However, because of the
close coupling between them, you might instinctively think that the two
conductors would still simply act as a single conductor, and the feed
impedance would be low (more like a non-folded monopole).

Can't you make a trapped dipole (or whatever) using 300 twin for each
leg, but with sections of one conductor cut out so you form a succession
of 1/4WL shorted stubs (of various lengths) in series, acting as traps
on the various HF bands?
--
Ian

You are thinking about the Lattin Antenna -- there's
lots of info available on the net for it. Instead of a dipole,
you could use one half the dipole as a vertical

Irv VE6BP


"Ian Jackson" wrote in message
...
In message , W5DXP
writes
On Friday, June 7, 2013 4:42:13 PM UTC-5, Ian Jackson wrote:
... one side is fed from the TX, and the other side is open circuit.

The 1/4WL folded monopole is resonant with a feedpoint impedance around
three times a 1/4WL single-wire monopole. Those two antennas have
approximately the same gain.

If one disconnects the folded element's ground connection leaving an
open-circuit, the feedpoint reactance becomes extremely high and the
antenna loses about 6dB of gain compared to the standard 1/4WL monopole.
It looks more like a 1/4WL shorted stub than an antenna.

I thought something like that would happen. However, because of the close
coupling between them, you might instinctively think that the two
conductors would still simply act as a single conductor, and the feed
impedance would be low (more like a non-folded monopole).

Can't you make a trapped dipole (or whatever) using 300 twin for each leg,
but with sections of one conductor cut out so you form a succession of
1/4WL shorted stubs (of various lengths) in series, acting as traps on the
various HF bands?
--
Ian

In message , Irv Finkleman
writes
"Ian Jackson" wrote in message
...
In message , W5DXP
writes
On Friday, June 7, 2013 4:42:13 PM UTC-5, Ian Jackson wrote:
... one side is fed from the TX, and the other side is open circuit.

The 1/4WL folded monopole is resonant with a feedpoint impedance around
three times a 1/4WL single-wire monopole. Those two antennas have
approximately the same gain.

If one disconnects the folded element's ground connection leaving an
open-circuit, the feedpoint reactance becomes extremely high and the
antenna loses about 6dB of gain compared to the standard 1/4WL monopole.
It looks more like a 1/4WL shorted stub than an antenna.

I thought something like that would happen. However, because of the close
coupling between them, you might instinctively think that the two
conductors would still simply act as a single conductor, and the feed
impedance would be low (more like a non-folded monopole).

Can't you make a trapped dipole (or whatever) using 300 twin for each leg,
but with sections of one conductor cut out so you form a succession of
1/4WL shorted stubs (of various lengths) in series, acting as traps on the
various HF bands?
--
You are thinking about the Lattin Antenna -- there's
lots of info available on the net for it. Instead of a dipole,
you could use one half the dipole as a vertical

Irv VE6BP

Yup. That's the one. Thanks.
--
Ian

If the twin-lead portion is lambda/4 x Velocity factor,
and you add sufficient wire to the end to extend the
total length to lambda/4 you will find it gives a
reasonably good match to 52ohm coax. I built one
once. It went halfway up my tower and was then folded off at an angle and
the top end tied to to a fence.
It was cut for 75M and was a remarkable performer.

A chum of mine who DXes the low bands put one
up and really liked it. The antenna is described in Bill
Orr's book "All About Vertical Antennas".

Irv VE6BP

"Ian Jackson" wrote in message
...
In message , W5DXP
writes
On Thursday, June 6, 2013 8:34:04 AM UTC-5, Geoffrey S. Mendelson wrote:
What do I have?

http://en.wikipedia.org/wiki/Folded_unipole_antenna
--
73, Cecil, w5dxp.com

I think what Geoff is describing is not the usual folded unipole (twin
feeder shorted at the top, and at the bottom, one side fed from the TX,
and the other side grounded and/or connected to radials), but rather twin
feeder where the top end is shorted, and at the bottom, one side is fed
from the TX, and the other side is open circuit.
--
Ian