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 Friday, November 7, 2014 11:22:30 PM UTC-6, amdx wrote:

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

With me, I just don't have time to do something I've already done
several times years ago.. I know pretty much from what I've already
modeled, what works and what doesn't. I used to have loads and loads
of stored antennas I modeled, but like I say, it's all on old drives
I don't use any more.
As I seem to recall, Jerry Sevick knows his stuff, so you won't go wrong
with that book.

amdx wrote in :

what materials
can you get, and then design around them.

I'll risk looking like a devil's advocate here and suggest good austenitic
stainless steel, like 316, for wires and radials, as a first base.
Reasons:
1. Cheaper than copper.
2. Stronger than copper.
3. If after a bit of stretching, a strong NdFeB magnet shows total
indifference to it when introduced, it permeability is likely low enough to
ignore if you're doing a first, empirical test of an antenna.
4. Very good chemical resistance, eliminating a whole heap of environmental
concerns for its endurance and performance.
5. Very good physical resistance, so no need to cover with insulator, thus no
need to add that into high frequency modelling.
6. Easy to find all over eBay...

I'm sure there are things I didn't think of, and if there is some vitally
specific reason not to do this, you'll likely already know it, but my point
is that if you just want to get something tried out first, economically, it
is likely better this way than starting with copper, for the simple reason
that if it fails, the stainless stuff will do you good service in some other
way, sometime, and wasted copper is less useful, and loses money very fast.