I am doing some design with vertical antennas for the low bands
40/80/160M. I require a somewhat large reactance on the element to
help load it on 160M, (40&80M) are working somewhat satisfactory now
with the design i am using. The required reactance that i need and the
size it would be using a coil (with the materials that i have right
now) may not last a winter storm in VO1 land when loaded with ice or
snow in 90km/h wind, so my question is, has anyone had experience
using a toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

wrote:
... has anyone had experience
using a toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

I've only one data point based on measurements made
at a California 75m mobile shootout.

K7JEB had this one mounted on a full-sized pickup.
An 8.5 foot whip using a 75m Texas Bugcatcher coil
at the base outperformed my antenna by +7dB.

I had this one mounted on a full-sized pickup.
An 11.5 foot whip using an SG-230 autotuner at the
base.

Not exactly the comparison you are seeking but the
SG-230 did use #2 iron powder toroidal inductors.

One might assume that the 6 inch long air-core
bugcatcher coil contributed more radiation than the
toroidal inductors. Seems to me the large air-core
coil occupies a greater number of degrees of antenna
than does toroidal inductor. This could be proved
(or disproved) by making delay measurements on both
coils using traveling wave current.

Previous such measurements are worthless for such
because the total current used was primarily standing-
wave current and was changing phase by only ~1 deg
for every ~30 degrees of antenna wire or coil.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Mar 28, 2:10*pm, Cecil Moore wrote:
wrote:
... has anyone had experience
using a *toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

I've only one data point based on measurements made
at a California 75m mobile shootout.

K7JEB had this one mounted on a full-sized pickup.
An 8.5 foot whip using a 75m Texas Bugcatcher coil
at the base outperformed my antenna by +7dB.

I had this one mounted on a full-sized pickup.
An 11.5 foot whip using an SG-230 autotuner at the
base.

Not exactly the comparison you are seeking but the
SG-230 did use #2 iron powder toroidal inductors.

One might assume that the 6 inch long air-core
bugcatcher coil contributed more radiation than the
toroidal inductors. Seems to me the large air-core
coil occupies a greater number of degrees of antenna
than does toroidal inductor. This could be proved
(or disproved) by making delay measurements on both
coils using traveling wave current.

Previous such measurements are worthless for such
because the total current used was primarily standing-
wave current and was changing phase by only ~1 deg
for every ~30 degrees of antenna wire or coil.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Thanks for your reply and the information you provided, it was very
useful as well as the link, it will take me a bit to check it out LOTS
of info there as well.
I'm trying 40/80/160M trap vertical ,i'm experimenting with the low
pass filters in the vertical as coil and cap hats as opposed to coils
and coax capacitors or mica caps which ever. I would like to use the
hats to distribute the current along the radiators more uniform as
opposed to linear. The insulator i have on hand for the top hat is
physically not long enough for the air core inductor, this is why i
was wondering about the toroid at the top. 40/80M works great for dx
with a 100W not bad on 15M either despite propagation lately. I should
also mention its noisy on rx, i see it sometimes has 40db more noise
then the loops that i used for rx, thanks again, 73 vo1bbn

Cecil Moore wrote:
Seems to me the large air-core
coil occupies a greater number of degrees of antenna
than does the toroidal inductor.

I've received a number of emails requesting that I
explain what I meant by this statement. It is easiest
understood by people who can solve the following
problem.

How can the impedance looking into the following
physical 45 degree, dual-Z0 stub be purely resistive,
i.e. electrically 90 degrees and resonant?

---22.5 deg 300 ohm twinlead---+---22.5 deg 50 ohm coax---open
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Mar 30, 4:39*pm, Cecil Moore wrote:
Cecil Moore wrote:
Seems to me the large air-core
coil occupies a greater number of degrees of antenna
than does the toroidal inductor.

I've received a number of emails requesting that I
explain what I meant by this statement. It is easiest
understood by people who can solve the following
problem.

How can the impedance looking into the following
physical 45 degree, dual-Z0 stub be purely resistive,
i.e. electrically 90 degrees and resonant?

---22.5 deg 300 ohm twinlead---+---22.5 deg 50 ohm coax---open
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Exactly as my tests have shown me. Using a coil and toroid with given
same inductance say 20uH to achieve the same resonance the top part of
the vertical over the toroid was about 8" longer, then the top
portion of the vertical over the coil, just as you stated, More
electrical degrees in the coil than the toroid.
I was wondering if the self shielding properties of the toroid would
have contributed to this conclusion, and because of these properties,
the toroid not have any electrical degrees, so to speak, so when it
come to the radiating element it would need to be slightly longer to
see the electrical degrees for the wavelength or resonance frequency
injected into it. thanks again for the info.

wrote:
I was wondering if the self shielding properties of the toroid would
have contributed to this conclusion, and because of these properties,
the toroid not have any electrical degrees, so to speak, so when it
come to the radiating element it would need to be slightly longer to
see the electrical degrees for the wavelength or resonance frequency
injected into it. thanks again for the info.

I suspect that the VF of the toroidal loading coil is much
higher than the VF of an air-core loading coil, i.e. the
toroidal loading coil occupies fewer electrical degrees of
the antenna. It makes sense that if the toroidal loading
coil occupies fewer electrical degrees of the antenna that
those degrees must be furnished somewhere else. The toroidal
loading coil seems to be closer to the lumped circuit model
than is the large air-core loading coil which generally
requires analysis using distributed network techniques.

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

There are two things happening with a base loading coil.
The loading coil occupies a certain number of degrees,
e.g. ~36 degrees for a 75m bugcatcher coil. The stinger
occupies maybe ~11 degrees for a total of ~47 degrees.
The other ~43 degrees comes from the phase shift at the
impedance discontinuity between the coil and the stinger.

With a center loading coil, a few degrees are lost at
the impedance discontinuity between the base section and
the coil. That's why a larger coil is needed for a
center-loaded mobile antenna.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Apr 2, 8:33*am, Cecil Moore wrote:
wrote:
I was wondering if the self shielding properties of the toroid would
have contributed to this conclusion, and because of these properties,
the toroid not have any electrical degrees, so to speak, so when it
come to the radiating element it would need to be slightly longer to
see the electrical degrees for the wavelength or resonance frequency
injected into it. thanks again for the info.

I suspect that the VF of the toroidal loading coil is much
higher than the VF of an air-core loading coil, i.e. the
toroidal loading coil occupies fewer electrical degrees of
the antenna. It makes sense that if the toroidal loading
coil occupies fewer electrical degrees of the antenna that
those degrees must be furnished somewhere else. The toroidal
loading coil seems to be closer to the lumped circuit model
than is the large air-core loading coil which generally
requires analysis using distributed network techniques.

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

There are two things happening with a base loading coil.
The loading coil occupies a certain number of degrees,
e.g. ~36 degrees for a 75m bugcatcher coil. The stinger
occupies maybe ~11 degrees for a total of ~47 degrees.
The other ~43 degrees comes from the phase shift at the
impedance discontinuity between the coil and the stinger.

With a center loading coil, a few degrees are lost at
the impedance discontinuity between the base section and
the coil. That's why a larger coil is needed for a
center-loaded mobile antenna.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

I am a little confused, you say about the coil and the stinger
occupying a portion of the total 90 degrees, (I can follow this not a
problem), however I thought the purpose of the coil was to add
inductive reactance, due to the shortened length of the radiator, less
than 1/4 wave, therefore having a capacitive reactance overhaul. Let
the shortened vertical be 34-j234 ohms. My understanding is that
depending on on what the reactance is at some freq, I need to offset
this negative reactance with an equal positive reactance. I wasn't
looking at from a degrees point for view. Or is it just 6 of one, half
dozen of the other, both be equal just expressed differently, I like
the degrees point of view for a couple of other arrays I am
experimenting with. (long wires) I think it will simplify things a
whole lot. thanks again for the info and the links, very valuable
info. 73 brett

wrote:
I am doing some design with vertical antennas for the low bands
40/80/160M. I require a somewhat large reactance on the element to
help load it on 160M, (40&80M) are working somewhat satisfactory now
with the design i am using. The required reactance that i need and the
size it would be using a coil (with the materials that i have right
now) may not last a winter storm in VO1 land when loaded with ice or
snow in 90km/h wind, so my question is, has anyone had experience
using a toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

I have something simular and used a FT-240-61 torroid which I happened
to have to build a tapped inductor with a pair of relays to switch it
in/out for 80/160.

The antenna analyzer and radio say it seems to work OK.

Just be sure to pick a material appropriate for an inductor at those
frequencies and a size appropriate for the power you intend to run.


--
Jim Pennino

Remove .spam.sux to reply.

On Mar 28, 3:00*pm, wrote:
wrote:
I am doing some design with vertical antennas for the low bands
40/80/160M. I require a somewhat large reactance on the element to
help load it on 160M, (40&80M) are working somewhat satisfactory now
with the design i am using. The required reactance that i need and the
size it would be using a coil (with the materials that i have right
now) *may not last a winter storm in VO1 land when loaded with ice or
snow in 90km/h wind, so my question is, has anyone had experience
using a *toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

I have something simular and used a FT-240-61 torroid which I happened
to have to build a tapped inductor with a pair of relays to switch it
in/out for 80/160.

The antenna analyzer and radio say it seems to work OK.

Just be sure to pick a material appropriate for an inductor at those
frequencies and a size appropriate for the power you intend to run.

--
Jim Pennino

Remove .spam.sux to reply.

Thanks for the information, nice to see others have done some work
with this in the past.I could do the switch relay and use the same hat
on 160 as i am now on 80, this overhaul length would be about 45 feet
not bad on 80 but i'm think a little short for efficiency on 160, with
the insulator i have on top of the 45 feet i can go another 12 feet to
the 160M hat. 57 feet overhaul to see how that works out. I do have an
option for an 18 feet fiberglass on that for 75 feet total but would
like to stick to 57 feet max any higher than that it will be quite
noticeable with the sun on the fiberglass over the tree line, i will
consider though your thought maybe not worth the gain in efficiency to
go the other 12 feet to the 160M hat, its maybe about 8-10 electrical
degrees in vertical radiator to the 160M top hat, thanks again great
info,73 vo1bbn

wrote:
I am doing some design with vertical antennas for the low bands
40/80/160M. I require a somewhat large reactance on the element to
help load it on 160M, (40&80M) are working somewhat satisfactory now
with the design i am using. The required reactance that i need and the
size it would be using a coil (with the materials that i have right
now) may not last a winter storm in VO1 land when loaded with ice or
snow in 90km/h wind, so my question is, has anyone had experience
using a toroid wound with the correct amount of reactance installed
on the element to to achieve resonance instead of a coil and how it
has been for them.

In most applications you'd be concerned about the inductor Q, since
higher Q means less loss for the same inductance. You probably won't be
able to get as high Q with a toroid as you will with a good air core
inductor.

But Tom, W8JI pointed out that with mobile antennas on the low frequency
bands, the ground loss is so much greater than loading inductor loss,
the latter isn't usually an important factor. It'll be difficult to get
really low ground loss with a fixed antenna, too, so a toroid should
work just about as well in practice unless you have a very good ground
system.

You don't, though, want the Q to be outrageously low. And that can
happen if water gets between the turns. (That's also true of an air
wound inductor.) So I recommend putting it into a container or coating
it to keep that from happening.

I built a toroid-loaded quarter wavelength (half length) 40 meter dipole
for Field Day, and measured the gain relative to a full size dipole. The
loss due to the inductors was less than a dB.

Expect a very narrow bandwidth if the loss is low.

Roy Lewallen, W7EL