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?

On 11/6/2014 7:08 PM, wrote:
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.

Nice work, Jim.

I can't get a picture in my head of how additional folded elements are
added. Can you elaborate a bit?

Thanks.

John

"John S" wrote in message ...

On 11/6/2014 7:08 PM, wrote:
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.

# Nice work, Jim.

# I can't get a picture in my head of how additional folded elements are
# added. Can you elaborate a bit?

3 Thanks.

# John

I'll comment, just to see if I'm envisioning his configuration properly.

If a folded dipole is constructed, the feedpoint impedance can be increased
by adding another parallel wire, forming a 3 wire folded dipole. A 5 wire
paralleled folded dipole would have an even higher feedpoint impedance.

So if I envision the configuration correctly, half of a 5 wire folded dipole
is used to construct a 5 wire folded vertical monopole.

The antenna is then shortened (but resonated) by putting a loading coil in
each of the 5 wires.

Total coil losses are lower because only 1/5 of the current flows through
each, giving each a resistance loss of (1/5*I)^2*R.

Is that it?

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

Wayne wrote:


"John S" wrote in message ...

snip

I'll comment, just to see if I'm envisioning his configuration properly.

If a folded dipole is constructed, the feedpoint impedance can be increased
by adding another parallel wire, forming a 3 wire folded dipole. A 5 wire
paralleled folded dipole would have an even higher feedpoint impedance.

So if I envision the configuration correctly, half of a 5 wire folded dipole
is used to construct a 5 wire folded vertical monopole.

The antenna is then shortened (but resonated) by putting a loading coil in
each of the 5 wires.

Yep, that's it.

Total coil losses are lower because only 1/5 of the current flows through
each, giving each a resistance loss of (1/5*I)^2*R.

Is that it?

I would have to go back to the model to see the relation of the central
current to the current in the four legs.

--
Jim Pennino

On 11/7/2014 11:40 AM, Wayne wrote:


"John S" wrote in message ...

On 11/6/2014 7:08 PM, wrote:
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.

# Nice work, Jim.

# I can't get a picture in my head of how additional folded elements are
# added. Can you elaborate a bit?

3 Thanks.

# John

I'll comment, just to see if I'm envisioning his configuration properly.

If a folded dipole is constructed, the feedpoint impedance can be
increased by adding another parallel wire, forming a 3 wire folded
dipole. A 5 wire paralleled folded dipole would have an even higher
feedpoint impedance.

That first sentence did it for me, Wayne. Thanks. I now understand
completely.

So if I envision the configuration correctly, half of a 5 wire folded
dipole is used to construct a 5 wire folded vertical monopole.

The antenna is then shortened (but resonated) by putting a loading coil
in each of the 5 wires.

Total coil losses are lower because only 1/5 of the current flows
through each, giving each a resistance loss of (1/5*I)^2*R.

Is that it?

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 Fri, 7 Nov 2014 01:08:33 -0000, wrote:

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.

Idea: There are times when matching to 50 ohms isn't the best
approach. I had that problem once and decided that the solution was
to move the power amplifier stage to the antenna. With an emitter
follower power output stage, I was able to get source impedances of
less than 1 ohms fairly easily. The base of the emitter follower
ended up about 100 ohms, which was easily matched to 50 ohms with a
transformer.

The big problem was keeping the emitter followers stable. The usual
ferrite bead on the emitter leads helped, but did not provide
unconditional stability throughout the range of antenna tuning. I
never did stabilize the amplifier mostly because this was new to me at
the time and I didn't have decent models of the components involved.

Another problem was the high currents required that everything be big,
silver brazed, silver soldered, and expensive. Using silver plated
tubing seems to work best. I was playing with milliohms and spent
much time with a Kelvin bridge measuring tiny resistances. The worst
problem was that the antenna also had to handle the high currents,
which required heavy construction, thick plating, and lots of silver.
Most of the current flows in roughly the first 3 * skin depth. At
1.8MHz, that would be about 0.15 mm. I didn't think the world was
ready for silver plated antennas, but it was worth trying.

Ever see a lock washer glow red? That was fun.

Fortunately, it was a symmetrical antenna so I didn't need to deal
with high RF currents through a counterpoise (i.e. grounding system).

Using cut-n-try and copious overtime, I managed to deliver a prototype
that mostly worked. The fatal flaw was that the customer wasn't too
thrilled with having a fairly complex system split between two
locations (transmitter building and tower shack) and supply high
currents via garden hose size cables between sites. When lightning
hit nearby and blew up the output stage and most of the attached
monitoring equipment, it was decided to use a more conventional
design. I was not disappointed as I was seriously worried how I was
going to make it work reliably. Fortunately, the split site might not
be a major problem for ham use.

For 160 meter operation, I think this can be a useful method if the
power levels were kept low enough to prevent meltdown.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558