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.

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 1:46:18 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.

On Wednesday, November 5, 2014 2:04:29 PM UTC-6, wrote:

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,

Hummm, that is wrong. The base of the coil is at the 6 ft level,
not 5..

On 11/5/2014 1:08 PM, 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.
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.


OK, nuff jabbering.
I'll set the rules 15ft tall, designed for 80 meters.
16 radials, base mounted inductor and whatever tophat you desire.
Do the theoretical design find the feed impedance with some efficiency
numbers.
Then compare data to a dipole at 1/4 wave height.

Ready Set GO!

Wait, do you have a better idea than a base mounted inductor?
How long are the radials?
Do you want to compare 8 to 16 radials.
The tophat needs to survive 80 mile an hr wind.
I'm sure there's more.

Mikek

On 11/6/2014 7:16 AM, amdx wrote:
On 11/5/2014 1:08 PM, 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.
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.


OK, nuff jabbering.
I'll set the rules 15ft tall, designed for 80 meters.
16 radials, base mounted inductor and whatever tophat you desire.
Do the theoretical design find the feed impedance with some efficiency
numbers.
Then compare data to a dipole at 1/4 wave height.

Ready Set GO!

Wait, do you have a better idea than a base mounted inductor?
How long are the radials?
Do you want to compare 8 to 16 radials.
The tophat needs to survive 80 mile an hr wind.
I'm sure there's more.

Mikek

What wire material/size? Some stainless steel rods might have a
permeability that will reduce the efficiency. It will certainly have a
higher resistance than copper. Also note that copper-clad steel must
have a cladding several times the skin depth for high efficiency.

John

On 11/6/2014 7:16 AM, amdx wrote:
On 11/5/2014 1:08 PM, 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.
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.


OK, nuff jabbering.
I'll set the rules 15ft tall, designed for 80 meters.
16 radials, base mounted inductor and whatever tophat you desire.
Do the theoretical design find the feed impedance with some efficiency
numbers.
Then compare data to a dipole at 1/4 wave height.

Ready Set GO!

Wait, do you have a better idea than a base mounted inductor?

As Mark said, maybe 50-75% along the antenna.

How long are the radials?

How much space can you give us?

Do you want to compare 8 to 16 radials.

We can do that. (Or you can do it yourself with EZNEC)

The tophat needs to survive 80 mile an hr wind.

I don't know how to do that.

I'm sure there's more.

Yes, always.

Mikek


John

On 11/6/2014 10:56 AM, John S wrote:
On 11/6/2014 7:16 AM, amdx wrote:
On 11/5/2014 1:08 PM, 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.
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.


OK, nuff jabbering.
I'll set the rules 15ft tall, designed for 80 meters.
16 radials, base mounted inductor and whatever tophat you desire.
Do the theoretical design find the feed impedance with some efficiency
numbers.
Then compare data to a dipole at 1/4 wave height.

Ready Set GO!

Wait, do you have a better idea than a base mounted inductor?

As Mark said, maybe 50-75% along the antenna.

How long are the radials?

How much space can you give us?

Do you want to compare 8 to 16 radials.

We can do that. (Or you can do it yourself with EZNEC)

The tophat needs to survive 80 mile an hr wind.

I don't know how to do that.

I'm sure there's more.

Yes, always.

I don't have a radio so it is moot point to me. I was just trying to
get a design going, as there just seemed to be a lot of jabbering.
But, there are just so many variables and you do need to start with a
location, how much money are you going to spend, what materials
can you get, and then design around them.
I'm not an actual ham but I did read Jerry Sevicks book,
"The Short Vertical Antenna and Ground Radial"
http://tinyurl.com/p3rp2qe

Mikek

On Thursday, November 6, 2014 7:16:32 AM UTC-6, amdx wrote:

OK, nuff jabbering.
I'll set the rules 15ft tall, designed for 80 meters.
16 radials, base mounted inductor and whatever tophat you desire.
Do the theoretical design find the feed impedance with some efficiency
numbers.
Then compare data to a dipole at 1/4 wave height.

Ready Set GO!

I'll let you all do the actual design and calculating. All of
the software needed can be had free on the web.


Wait, do you have a better idea than a base mounted inductor?

If you use a large enough hat, it really doesn't matter where
the coil is as far as improving current distribution.

How long are the radials?

I dunno.. how much wire is available? How much room?
In general for a limited amount of wire, many short radials
are better than just a few long ones.

Do you want to compare 8 to 16 radials.

Neither one is really enough for top performance over avg ground
with a short vertical.

The tophat needs to survive 80 mile an hr wind.

Use guyed off wire spokes I suppose..

It depends on the path/distance, etc but in general a 1/2 wl dipole
at 1/4 wave is going to smoke most any short vertical of that appx
design. NVIS, HUGELY so.. far DX, might be a toss if the vertical
is performing well. But to really perform well, I'd want at least
60 radials, not 8-16.. In the real world, I generally wouldn't use
such an antenna unless it was all I could get away with.

With ground mount verticals, the shorter the antenna, the more
critical the ground radial system becomes.

On 80m, 99 percent of my jibber jabber is NVIS, and I'd be the laughing
stock of the frequency with such an antenna.
My signal would be quite puny, compared to my normal dipoles and such.
I'd be heckled and tormented endlessly to build a "real" antenna.
I ain't joking either. They can be a tough crowd out there. lol

Jeff wrote:
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.


A dipole may be a better candidate, if you use a monopole then although
you will be able to put your matching close to the antenna, providing an
effective earth screen becomes vital and earth losses may outweigh any
advantage.

Of course if you do use a dipole it is vital that any matching is at the
feed point and not on the end of a length of coax or the losses will soar.

The issue with dipoles is height.

As the height of a dipole decreases below 1/2 wavelength the pattern
elevation angle starts increasing and very quickly has most of the
energy going straight up.

At 160M that means getting the dipole 260 feet up in the air, and if
you can do that, why would you be concerned about a short antenna
as a full 1/4 wave 160M antenna is only about 140 feet tall?



--
Jim Pennino