Hi, Gentlemen -

What if we (just for fun and knowledge) design a short dipole antenna
together here in the group? How short should we go as a practical matter?

* What would be the worst input impedance we would would wish to deal
with? That will actually determine the shortness of the dipole, yes?

* There will be losses. How much are we willing to accept? This is
another determining factor to the shortness, yes?

* What might be the best feed arrangement for our short antenna? There
are lots of ways.

I don't know much about small loop antennas, but I can fade into the
shadows and try to learn from you.

Any other suggestions to this endeavor is also fine. Let's just discuss
what we enjoy doing. If you have other topics of small antennas, let's
put them on the table.

Gentlemanly arguments are welcome concerning the technical aspects of
our discussion. I have never had a problem with anyone who says "I
believe you are wrong in this assumption and here is why."

Thanks, Gentlemen.

Cheers,
John KD5YI

On Wednesday, November 5, 2014 10:56:53 AM UTC-6, John S wrote:
Hi, Gentlemen -

What if we (just for fun and knowledge) design a short dipole antenna
together here in the group? How short should we go as a practical matter?

* What would be the worst input impedance we would would wish to deal
with? That will actually determine the shortness of the dipole, yes?

* There will be losses. How much are we willing to accept? This is
another determining factor to the shortness, yes?

* What might be the best feed arrangement for our short antenna? There
are lots of ways.

I don't know much about small loop antennas, but I can fade into the
shadows and try to learn from you.

Any other suggestions to this endeavor is also fine. Let's just discuss
what we enjoy doing. If you have other topics of small antennas, let's
put them on the table.

Gentlemanly arguments are welcome concerning the technical aspects of
our discussion. I have never had a problem with anyone who says "I
believe you are wrong in this assumption and here is why."

Thanks, Gentlemen.

Cheers,
John KD5YI

In very general terms, I would design a small dipole the same as
I would design a mobile whip. Except I would have two of them
back to back. The design would include all the usual considerations
about loading coil location, top/end capacity hats, etc.
What is good for the car, is good for the house.

I have plenty of old software, much from Reg EdwardsSK, that can be
used to design the antenna, determine appx losses, determine the
number of turns for the loading coils, etc, etc.

And then use EZNEC or whatever modeler to test the final design
before going out to the garage to whip up the actual antenna.

On 11/5/2014 11:58 AM, wrote:
On Wednesday, November 5, 2014 10:56:53 AM UTC-6, John S wrote:
Hi, Gentlemen -

What if we (just for fun and knowledge) design a short dipole antenna
together here in the group? How short should we go as a practical matter?

* What would be the worst input impedance we would would wish to deal
with? That will actually determine the shortness of the dipole, yes?

* There will be losses. How much are we willing to accept? This is
another determining factor to the shortness, yes?

* What might be the best feed arrangement for our short antenna? There
are lots of ways.

I don't know much about small loop antennas, but I can fade into the
shadows and try to learn from you.

Any other suggestions to this endeavor is also fine. Let's just discuss
what we enjoy doing. If you have other topics of small antennas, let's
put them on the table.

Gentlemanly arguments are welcome concerning the technical aspects of
our discussion. I have never had a problem with anyone who says "I
believe you are wrong in this assumption and here is why."

Thanks, Gentlemen.

Cheers,
John KD5YI

In very general terms, I would design a small dipole the same as
I would design a mobile whip. Except I would have two of them
back to back. The design would include all the usual considerations
about loading coil location, top/end capacity hats, etc.
What is good for the car, is good for the house.

I have plenty of old software, much from Reg EdwardsSK, that can be
used to design the antenna, determine appx losses, determine the
number of turns for the loading coils, etc, etc.

And then use EZNEC or whatever modeler to test the final design
before going out to the garage to whip up the actual antenna.

That sounds great, Mark.

Can you tell us how big would it be? And what about the coil dimensions,
losses? Can you do an EZNEC model so those of us who have the simulator
can look at all the parameters/arguments?

Many thanks for your input.

John (who was KD5YI but will be N1JLS in a few weeks due to vanity)

John S wrote:
Hi, Gentlemen -

What if we (just for fun and knowledge) design a short dipole antenna
together here in the group? How short should we go as a practical matter?

* What would be the worst input impedance we would would wish to deal
with? That will actually determine the shortness of the dipole, yes?

* There will be losses. How much are we willing to accept? This is
another determining factor to the shortness, yes?

* What might be the best feed arrangement for our short antenna? There
are lots of ways.

I don't know much about small loop antennas, but I can fade into the
shadows and try to learn from you.

Any other suggestions to this endeavor is also fine. Let's just discuss
what we enjoy doing. If you have other topics of small antennas, let's
put them on the table.

Gentlemanly arguments are welcome concerning the technical aspects of
our discussion. I have never had a problem with anyone who says "I
believe you are wrong in this assumption and here is why."

Thanks, Gentlemen.

Cheers,
John KD5YI

I would think a dipole would be a bad candidate for a "short" antenna
as you need to get the matching stuff close to the antenna to avoid
I^2R losses.

Some sort of ground mounted, or close to the ground, antenna might
make a better choice.

Also needed is some sort of definition of "short", e.g. total volume
of the antenna constrained to some fraction of a wavelength.

One interesting technique for shortning an antenna can be seen by
lookup up US Patent 6,642,902.

Essentially it is a coax in a coax with internal shorting stubs
inside the coaxes with capacitive end loading. Too complex to
explain in words, but the drawings in the patent are clear.


--
Jim Pennino

On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote:


Can you tell us how big would it be? And what about the coil dimensions,
losses? Can you do an EZNEC model so those of us who have the simulator
can look at all the parameters/arguments?

It can be any size one wants. The bigger the better of course..
And all the other parameters can be adjusted also.. You use what
you can get away with to fit the room you have.
I don't recall having any mobile whips modeled, but it's hard to
say as all the older designs I did are on older unused hard drives
and I don't have ready access to them. I had to re-download quite
a few programs due to that reason.. I change drives quite often.
I just added two more 2 TB drives about a month ago.. I have several
TB these days.

All of Reg's old software can still be downloaded.
http://zerobeat.net/G4FGQ/page3.html#S301%22
Vertload was one I used a lot for playing "what if" when designing
mobile whips and other short verticals, and the info can easily
be used for small dipoles. There are others programs that can be
handy also.

It's been a long time since I used it, but I believe vertload
can be used to locate the best location on the whip to place
the loading coil. In general, you want it as far out to the ends
as possible for the best current distribution, but there is a
point where coil losses start to outweigh the improved current
distribution. So in the real world, the best location is usually
appx 3/4 the way out from the feedpoint, plus or minus.

And the use of capacity hats further improve current distribution,
and slightly reduce the number of turns needed for the loading
coil. A short dipole is never going to be quite as good as a full
size version, but with proper design you can come up with quite a
respectable antenna given the dinky size.



John (who was KD5YI but will be N1JLS in a few weeks due to vanity)

Hummm.. You now in 1 land, or you just grabbing an old call?
My current call is a vanity call, which I think I've had since '96.
I was WD5CJL in a past life.. I got that call in 77 when I was 20.

I actually got into ham radio when I was in the eighth grade, learned
the code, and even built a 6v6 transmitter from junk parts.
But then I got lazy and kind of got out of it a while, and didn't
actually get a ticket. Later on I got back into it, and got a ticket about
six years later. I used my first 6v6 transmitter when I was a novice in 77.
I was a SWL for a good while before I got into ham radio.
I worked a lot of CW back in the old days. I got up to nearly 60 wpm
at one point. But due to lack of activity the past several years, I can't
do near that now.

On Wednesday, November 5, 2014 1:01:02 PM UTC-6,
I would think a dipole would be a bad candidate for a "short" antenna
as you need to get the matching stuff close to the antenna to avoid
I^2R losses.

I'd probably use small matching coils at the feed point, about the
same as a mobile antenna.
In the real world, I try to avoid short antennas..
It's only a last resort due to lack of room. I rarely actually use one.

On 11/5/2014 2:02 PM, wrote:
On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote:


Can you tell us how big would it be? And what about the coil dimensions,
losses? Can you do an EZNEC model so those of us who have the simulator
can look at all the parameters/arguments?

It can be any size one wants. The bigger the better of course..

What? Maybe you don't fully grasp the idea of a "short" antenna? ;-)

--

Rick

wrote:
On Wednesday, November 5, 2014 1:01:02 PM UTC-6,
I would think a dipole would be a bad candidate for a "short" antenna
as you need to get the matching stuff close to the antenna to avoid
I^2R losses.

I'd probably use small matching coils at the feed point, about the
same as a mobile antenna.

There is a lot of stuff out there that says the best place to put
a loading coil is somewhere between 1/2 and 3/4 of the way up.

It should be fairly easy to model to see where it would be for
various total lengths.

In the real world, I try to avoid short antennas..
It's only a last resort due to lack of room. I rarely actually use one.

Me too for the most part.

I've never felt a need to go mobile any lower than 10M though I have
put some thought into shortning 160M antennas.

One concept I started playing with but never finished was the folded
monopole, i.e. half of a folded dipole, but with more than one "folded"
element in an attempt to get the radiation resistance up.


--
Jim Pennino

On Wednesday, November 5, 2014 1:33:06 PM UTC-6, rickman wrote:
On 11/5/2014 2:02 PM, wrote:
On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote:


Can you tell us how big would it be? And what about the coil dimensions,
losses? Can you do an EZNEC model so those of us who have the simulator
can look at all the parameters/arguments?

It can be any size one wants. The bigger the better of course..

What? Maybe you don't fully grasp the idea of a "short" antenna? ;-)

--

Rick

I grasp that the shorter the antenna, the worse it generally performs.
But if I use an 18 ft long dipole for 80 or 40 meters, I consider
that a short dipole. Others may disagree, but I don't care.
They can knock themselves out with shorter versions.
I try to avoid using short dipoles. My previously mentioned methods
can be used with any length dipole. The smaller, the smaller the
performance.
Of course, the reasons for the smaller performance are not
what he who is silly thinks are the reasons. :|

On Wednesday, November 5, 2014 1:46:18 PM UTC-6, wrote:
wrote:
On Wednesday, November 5, 2014 1:01:02 PM UTC-6,
I would think a dipole would be a bad candidate for a "short" antenna
as you need to get the matching stuff close to the antenna to avoid
I^2R losses.

I'd probably use small matching coils at the feed point, about the
same as a mobile antenna.

There is a lot of stuff out there that says the best place to put
a loading coil is somewhere between 1/2 and 3/4 of the way up.

My usual 11 ft 80-10m mobile antenna in the driving mode is exactly
center loaded. The coil bottom is at the 5 ft point, and there is
a 5 ft "stinger whip" above it. The coil itself is about a foot long
and has taps for the various bands. I use shorter stinger whips for
the higher bands.

But in the parked mode, I have a solid three foot mast that I screw
onto the base of the main whip, and the coil is at the 8ft level.
It makes quite a difference in efficiency. I don't use a hat on my
mobile antennas because I think they are ugly, and catch too much wind.

I also have a screwdriver antenna I got free, but it's inferior to my
homemade "plastic bugcatchers", and I've never used it. It sits in the
garage and collects dust.

I've used a 706mk2g as the mobile rig since about 2001 or so. But I
recently picked up a FT-100 which could be used also. I also have the
matching auto tuner for that rig, but not sure if I would ever use it.
I don't need it for my usual mobile whips as they are matched with the
"dollar special" matching coils.


It should be fairly easy to model to see where it would be for
various total lengths.

Yep.. I think vertload will do it if I'm remembering the right program.


In the real world, I try to avoid short antennas..
It's only a last resort due to lack of room. I rarely actually use one.

Me too for the most part.

I've never felt a need to go mobile any lower than 10M though I have
put some thought into shortning 160M antennas.

I've had a 80-10 mobile antenna for many years. When parked, I've
used it on 160m by clipping on a longer wire above the coil.
Both of my trucks have antenna ball mounts. But the Toyota car I
drive does not have anything, because I'm chicken to booger up the
pristine body with holes and such.. :/


One concept I started playing with but never finished was the folded
monopole, i.e. half of a folded dipole, but with more than one "folded"
element in an attempt to get the radiation resistance up.

I've never tried anything like that.