In the last installment we got the input impdance up to the order of
2 Ohms with loading and a top hat.

2 Ohms will still lead to lots of loss in the matching device, so let's
see if the input impedance can be further increased.

Those familiar with the folded dipole are aware that the input impedance
of a folded dipole is higher than a dipole, so let's try a folded
monopole and see what happens.

I started with a single folded element spaced at 2 feet from the central
radiator that drops down and connects to a radial.

That brought the impedance up to about 4 Ohms.

If a little is good, more must be better so I added a second folded
element and got about 12 Ohms.

Going for the gusto, I then added 2 more folded elements for a total
of 4 as well as adding a loading inductor into all elements starting
at the 50% level and let the optimizer have at it to optimize the
inductance and inductor height for SWR and gain.

When it finished, here is what I got:

Impedance: 41.32 -9.5 Ohms
SWR: 1.3:1
gain: 1.1 dBi @ 25 degrees
Inductors: 787 uH

So here we have a 0.029 wavelength antenna that is only about 2 dB
down from a full 0.25 antenna and can be fed directly from a 50 Ohm
transmitter without any matching device losses.

As an aside, the differences between zero resistance and copper were
insignificant as one would expect with this input impedance.

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

Next I added the 7.5' top hat radials and let the optimizer go at it
once more achieving:

Impedance: 58.83 -6.1 Ohms
SWR: 1.5:1
gain: 1.5 dBi @ 25 degrees
Inductors: 577 uH

Not a significant decrease in the inductance as with a single element
and the change in bandwidth was trivial. In this case I don't think
the top hat is worth the bother.

The practical issues with this antenna is getting 5 adjustable inductors
so the antenna is usable over a broader range and as the current in
the inductors is a bit high, they would have to be good adjustable
inductors.

At this point I think the notion that "short antennas are inefficient"
can be regarded as nonsense and the choice boils down to bandwith/size,
pick one.

Next up, a 160M rubber ducky, but only after attending to some roof
leaks revealed by recent rain.


--
Jim Pennino

wrote in message ...

In the last installment we got the input impdance up to the order of
2 Ohms with loading and a top hat.

2 Ohms will still lead to lots of loss in the matching device, so let's
see if the input impedance can be further increased.

Those familiar with the folded dipole are aware that the input impedance
of a folded dipole is higher than a dipole, so let's try a folded
monopole and see what happens.

I started with a single folded element spaced at 2 feet from the central
radiator that drops down and connects to a radial.

That brought the impedance up to about 4 Ohms.

If a little is good, more must be better so I added a second folded
element and got about 12 Ohms.

Going for the gusto, I then added 2 more folded elements for a total
of 4 as well as adding a loading inductor into all elements starting
at the 50% level and let the optimizer have at it to optimize the
inductance and inductor height for SWR and gain.

When it finished, here is what I got:

Impedance: 41.32 -9.5 Ohms
SWR: 1.3:1
gain: 1.1 dBi @ 25 degrees
Inductors: 787 uH

So here we have a 0.029 wavelength antenna that is only about 2 dB
down from a full 0.25 antenna and can be fed directly from a 50 Ohm
transmitter without any matching device losses.

As an aside, the differences between zero resistance and copper were
insignificant as one would expect with this input impedance.

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

Next I added the 7.5' top hat radials and let the optimizer go at it
once more achieving:

Impedance: 58.83 -6.1 Ohms
SWR: 1.5:1
gain: 1.5 dBi @ 25 degrees
Inductors: 577 uH

Not a significant decrease in the inductance as with a single element
and the change in bandwidth was trivial. In this case I don't think
the top hat is worth the bother.

The practical issues with this antenna is getting 5 adjustable inductors
so the antenna is usable over a broader range and as the current in
the inductors is a bit high, they would have to be good adjustable
inductors.

At this point I think the notion that "short antennas are inefficient"
can be regarded as nonsense and the choice boils down to bandwith/size,
pick one.

Next up, a 160M rubber ducky, but only after attending to some roof
leaks revealed by recent rain.


--
Jim Pennino

%%%%%%%%%%%%

Interesting. I think I follow the design.

Could you increase the bandwidth by tuning the various paralleled parts to
slightly different frequencies?

wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
..96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.



--
Jim Pennino

On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

Okay, but the starting target was to be able to feed a short antenna
with good efficiency and I think you hit that target. I know you want to
keep it as practical as possible, but I am impressed with your results.

John S wrote:
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

Okay, but the starting target was to be able to feed a short antenna
with good efficiency and I think you hit that target. I know you want to
keep it as practical as possible, but I am impressed with your results.

Thanks.

The whole point of the exercise was to show there are way to overcome
the generally low impedance of short antennas.

I did notice the resident gas bag has nothing to say about posts containing
numbers. It appears numbers are his kyptonite.


--
Jim Pennino

On 11/8/2014 10:45 AM, wrote:
John S wrote:
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

Okay, but the starting target was to be able to feed a short antenna
with good efficiency and I think you hit that target. I know you want to
keep it as practical as possible, but I am impressed with your results.

Thanks.

The whole point of the exercise was to show there are way to overcome
the generally low impedance of short antennas.

Exactly! It was a challenge which has been shown to be surmountable by
design. Feed losses become less of a burden this way.

Do you think your results could be practical? Could ground resistance be
used to widen the BW? I know, there are losses. But, maybe worth it?

What do you think?

John S wrote:
On 11/8/2014 10:45 AM, wrote:
John S wrote:
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

Okay, but the starting target was to be able to feed a short antenna
with good efficiency and I think you hit that target. I know you want to
keep it as practical as possible, but I am impressed with your results.

Thanks.

The whole point of the exercise was to show there are way to overcome
the generally low impedance of short antennas.

Exactly! It was a challenge which has been shown to be surmountable by
design. Feed losses become less of a burden this way.

Do you think your results could be practical? Could ground resistance be
used to widen the BW? I know, there are losses. But, maybe worth it?

What do you think?

I think if the goal is a practical antenna, the starting point should be
how high can you practically go keeping in mind that a 1/4 wave 160M is
on the order of 130 feet and in general the higher the greater the
bandwidth and the less you have to be concerned with minimizing losses.

In my urban lot, anything over about 30 feet becomes a problem.

I do have a 33 foot tall vertical in the back yard with an autotuner
at the base. It started out as just a 40M vertical.

With the addition of the autotuner, it will tune and load 160 through
6 M. The performance on 6M is horrible as it is a cloud warmer at
that frequency, but most of the other bands are OK or better.

The 160 and 80 performance was poor, which I attibuted to losses in
the tuner, so I put in a relay controlled high Q tapped coil to take
some of the burden off of the autotuner on those bands. That helped
quite a bit.

I have been thinking about using the folded monopole technique to
further improve things.

That would require some more relays to switch the folded parts into
the main radiator, essentially making it a fat radiator on other bands.

The biggest issue is mechanical so until I figure out that part, I
have left that project on the back burner for now.


--
Jim Pennino

"John S" wrote in message ...

On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

# Okay, but the starting target was to be able to feed a short antenna
# with good efficiency and I think you hit that target. I know you want to
# keep it as practical as possible, but I am impressed with your results.

I agree. I like the approach.

Anyone ready to tackle a fractal design

On 11/8/2014 10:57 AM, Wayne wrote:


"John S" wrote in message ...
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

# Okay, but the starting target was to be able to feed a short antenna #
with good efficiency and I think you hit that target. I know you want to
# keep it as practical as possible, but I am impressed with your results.

I agree. I like the approach.

Anyone ready to tackle a fractal design


I have no idea how to approach that, but I'm willing to read your posts
on it. Start by assuming zero knowledge for me.

On Saturday, November 8, 2014 11:15:33 AM UTC-6, John S wrote:
On 11/8/2014 10:57 AM, Wayne wrote:


"John S" wrote in message ...
On 11/7/2014 12:58 PM, wrote:
wrote:

snip

The only downside to this antenna is that it is extremely narrow
banded, only about a kHz or so.

snip

I realized I should expand on that.

With all 5 inductors the same value the 5:1 bandwidth is about 500 Hz.

By staggering the values of the inductors in the four legs the bandwidth
can be improved by a little bit.

The best I could accomplish was about 1 Khz by making the leg values
.96, .98, 1.02, and 1.04 times the central leg value.

Going beyond a step factor of .02 made little difference in the bandwidth
and the resonant frequency SWR started to increase.

# Okay, but the starting target was to be able to feed a short antenna #
with good efficiency and I think you hit that target. I know you want to
# keep it as practical as possible, but I am impressed with your results.

I agree. I like the approach.

Anyone ready to tackle a fractal design


And they say I like to stir it... lol


I have no idea how to approach that, but I'm willing to read your posts
on it. Start by assuming zero knowledge for me.

We thrashed that around quite a bit many moons ago.
Richard Clark in particular did quite a bit of pondering and puter
simulation on the subject.
http://www.qsl.net/kb7qhc/antenna/fractal/

I think the most chortle inducing moment was when a totally random
design outdid one that the guru of all things fractal spit out using
his highly self touted puter optimizations.

I came to the conclusion that fractal antennas were nothing more
than linear loading using pretty design schemes.
Often no real advantage to a random design drawn with the eyes closed,
but hey, if one can attract gov grants, contracts and such, using
advanced forms of bafflegab to lure in the gullible, one can overlook
such things while laughing all the way to the bank.

Actually, I consider any symmetrical antenna design to be a fractal
of sorts.. Even a dipole as the simplest form.