Jim Lux wrote:
Wayne wrote:
"Spin" wrote in message
...
Wayne........That's interesting.....Can you elaborate on that 2 meter
antenna you had? I wonder if one were to make a longer version would
it have gain & a wider bandwidth?


Sure. However, I'm not recommending it for anything. As I recall it
was a quarter wave of coax terminated in a 10 watt dummy load. The
quarter wave was connected as previously described, with the shield of
the quarter wave connected to the center conductor of the feedline and
the shield of the feedline connected to the center conductor of tthe
quarter wave. I was just trying to get a dummy load to radiate enough
for a short path to a repeater. (Transmitter ran 10 watts)

At a different time, I simply terminated a feedline (low quality
RShack RG-58) with a 10 watt carbon resistor (unshielded and 3 inch
leads). It worked about the same.

However, remember that I was only trying to hit a single repeater, and
a whip antenna with just a few milliwatts would have worked on that
particular path. The "antenna" was very poor, but there may be paths
where it is an acceptable compromise.


Think of this as a variant on taking a 1/4 wave of wire and attaching it
to the center conductor of the feedline (or, just stripping 1/4wave of
shield off the coax) with no choke, balun, or anything else. It's a sort
of sleeve dipole: The "outside" of the feedline coax essentially acts as
the other half of the dipole.

Depending on where it's installed, it might work, might not. No
decoupling means that the whole feedline potentially radiates, etc.
Probably no worse than a lot of other improvised antennas.

Put a really good choke around the coax at the 1/4 wave point, and it
starts to look better, but, having the feedline essentially hanging off
the end of the dipole means that you've got conductors in the high E
field part of the antenna, so there will be capacitive coupling.


Doing the Coro style thing with the resistor, etc, in effect makes this
another of the many "resistively loaded dipole" schemes where you give
up some efficiency in exchange for a better match. No different in
concept (although different in design) from the T2FD sorts of things
from B&W, etc.


I notice Arnie has a terminated, folded dipole or whatever you call it
on his web page. He doesn't offer it as anything other than what it is.
Most of his stuff has always been for people of limited means who still
want to enjoy amateur radio. Cubans are good at that type of thing
because their crappy economic system and the American boycott have
forced them to be that way.
73,
Tom Donaly, KA6RUH

On Thu, 5 Feb 2009 08:05:40 -0800, "Wayne"
wrote:

At one time, I lived in an apartment and used a similar, shorter antenna for
2 meter operation via a repeater. It was easy to build, and worked fine
because I didn't need much signal to hit the repeater.

Hi Wayne,

In my basement shack, using a 300mW 2M Alinco HT, I can hit my buddy's
repeater 10 miles away. The HT's antenna, fully extended, is only an
8 inch whip.

It doesn't need a resistor. It doesn't need fancy cable preparation.
It is roughly one-hundredth the size of Arnie's, operating at
one-twentieth the wavelength as Arnie's(?).

So, the amended Arnie's minimalist design:
1. Take a 45 ft/15 meter 52 ohm Coax;
2. connect center conductor and braid together on both ends;
3. throw a 50 OHM resistor over your right shoulder for luck;
4. then connect that coax through a tuner to your transceiver;
5. listen and talk to the world.

This pretty much describes my antenna that I could use to listen to
Radio Habana Cuba (and more) when I was a kid. However, I was driven
by economic necessity to be more minimalist. For instance:
1. Take a 45 ft/15 meter surplus armored 1" multi conductor cable;
2. strip out the wire from inside the cable for other projects;
3. keep the 50 OHM resistor for other projects;
4. then connect that cable shell through a tuner to my receiver;
5. listen to the world.

Using the armored shell was an extravagence, as I could have had used
one of the wires that formerly ran through it. That antenna heard
Habana, Quito, Sydney, and Cape Town (or Jo'burg) quite easily.

My radios back then were a Knight Kit Star Roamer, a BC348, a BC453,
and a RBB-1. I used the BC348 as a highly selective, second IF
(85kHz) conversion to the other sets.

73's
Richard Clark, KB7QHC

My radios back then were a Knight Kit Star Roamer, a BC348, a BC453,
and a RBB-1. I used the BC348 as a highly selective, second IF
(85kHz) conversion to the other sets.

73's
Richard Clark, KB7QHC

More likely, it was the BC-453 you used for the selectivity although it
wouldn't tune as high in frequency as the IF in the BC348. Must have used it
for the Knightkit

W4ZCB

Spin wrote:
Wayne........That's interesting.....Can you elaborate on that 2 meter
antenna you had? I wonder if one were to make a longer version would it
have gain & a wider bandwidth?

Just remember the general rule for antennas: small - efficient -
broadband: pick any two.

Roy Lewallen, W7EL

Sal M. Onella wrote:

Arnie Coro's website does discuss the item described.
http://www.mail-archive.com/hard-cor.../msg18595.html
He doesn't claim it works well (nor should he).

At one point he describes burying it to stealth it. When I was moving an
antenna, I had both dipole elements laying on the ground but still
connected. Just for laughs, I tuned it up. I could hear a few other people
but nobody could hear me. I think burying an HF antenna should be followed
by a shopping trip for some writing paper and stamps. You'll need 'em.


Buried antennas were seriously investigated by the military some time
ago, and are probably still in use. While terribly inefficient, some can
radiate enough to be useful, and invisibility can be an asset. I was
told long ago that the reason NEC-4 was prohibited for export for so
long was that it could be used for designing buried and therefore
invisible antennas.

Roy Lewallen, W7EL

Richard Clark wrote:

Dress right, or dress left?


Took some balls to ask that question... ;^)


- 73 de Mike N3LI -

On Thu, 05 Feb 2009 20:21:37 GMT, "Harold E. Johnson"
wrote:

My radios back then were a Knight Kit Star Roamer, a BC348, a BC453,
and a RBB-1. I used the BC348 as a highly selective, second IF
(85kHz) conversion to the other sets.

73's
Richard Clark, KB7QHC

More likely, it was the BC-453 you used for the selectivity although it
wouldn't tune as high in frequency as the IF in the BC348. Must have used it
for the Knightkit

Hi Harold,

You are right, I got the BCs backwards.

73's
Richard Clark, KB7QHC

Roy Lewallen wrote:
Sal M. Onella wrote:

Arnie Coro's website does discuss the item described.
http://www.mail-archive.com/hard-cor.../msg18595.html
He doesn't claim it works well (nor should he).

At one point he describes burying it to stealth it. When I was moving an
antenna, I had both dipole elements laying on the ground but still
connected. Just for laughs, I tuned it up. I could hear a few other
people
but nobody could hear me. I think burying an HF antenna should be
followed
by a shopping trip for some writing paper and stamps. You'll need 'em.


Buried antennas were seriously investigated by the military some time
ago, and are probably still in use. While terribly inefficient, some can
radiate enough to be useful, and invisibility can be an asset. I was
told long ago that the reason NEC-4 was prohibited for export for so
long was that it could be used for designing buried and therefore
invisible antennas.

Actually, I think it was the NEC 3 variant that first introduced buried
wires, and was classified as Defense Critical Technology. "The only
difference in the capabilities of these codes is that NEC-3 can model
wires that are buried or penetrate from air into the ground, while NEC-2
is limited to antennas in free space or above a ground plane."

from Burke's NEC validation paper published at that conference in Ankara
Turkey in 1989.

That paper also mentions an experimental version NEC3VLF (improving
performance for electrically small antennas), NEC4X (better modeling of
endcaps), NEC3I (for insulated wires), NEC-GS (ground screens), etc.,
all of which probably wound up in NEC4 in one way or another.

A notable export controlled application of such codes is modeling wires
submerged in seawater.

The export controls still exist, by the way, for NEC4.. when you get a
copy, don't you have to certify who the end user is? and agree to ITAR
compliance, etc.

https://ipo.llnl.gov/technology/soft...uments/NEC.pdf


Roy Lewallen, W7EL

"Jim Lux" wrote in message
...
Wayne wrote:
"Spin" wrote in message
...
Wayne........That's interesting.....Can you elaborate on that 2 meter
antenna you had? I wonder if one were to make a longer version would it
have gain & a wider bandwidth?


Sure. However, I'm not recommending it for anything. As I recall it was
a quarter wave of coax terminated in a 10 watt dummy load. The quarter
wave was connected as previously described, with the shield of the
quarter wave connected to the center conductor of the feedline and the
shield of the feedline connected to the center conductor of tthe quarter
wave. I was just trying to get a dummy load to radiate enough for a
short path to a repeater. (Transmitter ran 10 watts)

At a different time, I simply terminated a feedline (low quality RShack
RG-58) with a 10 watt carbon resistor (unshielded and 3 inch leads). It
worked about the same.

However, remember that I was only trying to hit a single repeater, and a
whip antenna with just a few milliwatts would have worked on that
particular path. The "antenna" was very poor, but there may be paths
where it is an acceptable compromise.

Think of this as a variant on taking a 1/4 wave of wire and attaching it
to the center conductor of the feedline (or, just stripping 1/4wave of
shield off the coax) with no choke, balun, or anything else. It's a sort
of sleeve dipole: The "outside" of the feedline coax essentially acts as
the other half of the dipole.

Depending on where it's installed, it might work, might not. No decoupling
means that the whole feedline potentially radiates, etc. Probably no worse
than a lot of other improvised antennas.

Put a really good choke around the coax at the 1/4 wave point, and it
starts to look better, but, having the feedline essentially hanging off
the end of the dipole means that you've got conductors in the high E field
part of the antenna, so there will be capacitive coupling.


Doing the Coro style thing with the resistor, etc, in effect makes this
another of the many "resistively loaded dipole" schemes where you give up
some efficiency in exchange for a better match. No different in concept
(although different in design) from the T2FD sorts of things from B&W,
etc.


The section of line at the end, terminated with the resistor, will present
something like 50 ohms between its terminals (outer and inner) at the point
where it is connected to the feedline, even if its terminals are reversed,
so if the outside surface of its outer conductor and the outside surface of
the outer conductor of the feedline present some sort of dipole to the same
point, the ~50 ohms will shunt the terminal impedance of that dipole. So if
the dipole actually radiates in the manner of a half-wave wire dipole its
VSWR could be improved by omitting the resistor.

Working: VSWR = (1+{Rho})/(1-{Rho}) where {Rho} is the magnitude of Rho, the
reflection coefficient for voltage at the dipole's drive point and Rho =
(ZL-Z0)/(ZL+Z0) where ZL is the impedance of the load at the end of the
feedline of characteristic impedance Z0.

~72 ohms from a half-wave dipole alone yields Rho = 0.16 for Z0 = 52 ohms,
and so VSWR = 1.38.

~72 in parallel with ~50 = ~29.5 ohms for the parallel combination yields
Rho = -0.28 so {Rho} = 0.28 and VSWR = 1.78.

Of course, if the 'dipole' does not radiate in the manner of a half-wave
wire dipole then this may not apply (e.g. if it is buried).

Chris

"christofire" wrote in message
...

"Jim Lux" wrote in message
...
Wayne wrote:
"Spin" wrote in message
...
Wayne........That's interesting.....Can you elaborate on that 2 meter
antenna you had? I wonder if one were to make a longer version would
it have gain & a wider bandwidth?


Sure. However, I'm not recommending it for anything. As I recall it
was a quarter wave of coax terminated in a 10 watt dummy load. The
quarter wave was connected as previously described, with the shield of
the quarter wave connected to the center conductor of the feedline and
the shield of the feedline connected to the center conductor of tthe
quarter wave. I was just trying to get a dummy load to radiate enough
for a short path to a repeater. (Transmitter ran 10 watts)

At a different time, I simply terminated a feedline (low quality RShack
RG-58) with a 10 watt carbon resistor (unshielded and 3 inch leads). It
worked about the same.

However, remember that I was only trying to hit a single repeater, and a
whip antenna with just a few milliwatts would have worked on that
particular path. The "antenna" was very poor, but there may be paths
where it is an acceptable compromise.

Think of this as a variant on taking a 1/4 wave of wire and attaching it
to the center conductor of the feedline (or, just stripping 1/4wave of
shield off the coax) with no choke, balun, or anything else. It's a sort
of sleeve dipole: The "outside" of the feedline coax essentially acts as
the other half of the dipole.

Depending on where it's installed, it might work, might not. No
decoupling means that the whole feedline potentially radiates, etc.
Probably no worse than a lot of other improvised antennas.

Put a really good choke around the coax at the 1/4 wave point, and it
starts to look better, but, having the feedline essentially hanging off
the end of the dipole means that you've got conductors in the high E
field part of the antenna, so there will be capacitive coupling.


Doing the Coro style thing with the resistor, etc, in effect makes this
another of the many "resistively loaded dipole" schemes where you give up
some efficiency in exchange for a better match. No different in concept
(although different in design) from the T2FD sorts of things from B&W,
etc.


The section of line at the end, terminated with the resistor, will present
something like 50 ohms between its terminals (outer and inner) at the
point where it is connected to the feedline, even if its terminals are
reversed, so if the outside surface of its outer conductor and the outside
surface of the outer conductor of the feedline present some sort of dipole
to the same point, the ~50 ohms will shunt the terminal impedance of that
dipole. So if the dipole actually radiates in the manner of a half-wave
wire dipole its VSWR could be improved by omitting the resistor.

Working: VSWR = (1+{Rho})/(1-{Rho}) where {Rho} is the magnitude of Rho,
the reflection coefficient for voltage at the dipole's drive point and Rho
= (ZL-Z0)/(ZL+Z0) where ZL is the impedance of the load at the end of the
feedline of characteristic impedance Z0.

~72 ohms from a half-wave dipole alone yields Rho = 0.16 for Z0 = 52 ohms,
and so VSWR = 1.38.

~72 in parallel with ~50 = ~29.5 ohms for the parallel combination yields
Rho = -0.28 so {Rho} = 0.28 and VSWR = 1.78.

Of course, if the 'dipole' does not radiate in the manner of a half-wave
wire dipole then this may not apply (e.g. if it is buried).

Chris

.... and replacing it with a short circuit! (important point, omitted from
posting)