Isotron ??
 

If I'm treading old ground please excuse the post. Today at the local
hamfest I ran across a 20 meter Isotron that the seller touting. After
looking at its simplicity and hearing how great it was I couldn't resist
because it was only $10.00. So now that I have it, I'm curious as to the
theory behind it and how an 89 turn coil of No. 12 wire on a 3/4" piece of
PVC along with a 12" aluminum rod and a couple of aluminum plates can load
and dissipate 1000 watts. I've seen their ads for years and always thought
they were snake oil but at $10.00 I bit. Anyone really know the theory
behind these things?
tnx
Hank WD5JFR

On Sat, 20 Mar 2004 22:15:52 GMT, "Henry Kolesnik"
wrote:

If I'm treading old ground please excuse the post. Today at the local
hamfest I ran across a 20 meter Isotron that the seller touting. After
looking at its simplicity and hearing how great it was I couldn't resist
because it was only $10.00. So now that I have it, I'm curious as to the
theory behind it and how an 89 turn coil of No. 12 wire on a 3/4" piece of
PVC along with a 12" aluminum rod and a couple of aluminum plates can load
and dissipate 1000 watts. I've seen their ads for years and always thought
they were snake oil but at $10.00 I bit. Anyone really know the theory
behind these things?
tnx
Hank WD5JFR


Hi Hank,

This intersects with so many recent topics, it is hard to know where
to begin.

First, undoubtedly through the combination of capacitance (the plates)
the inductance (the windings) and radiation resistance, it resonates
and sheds heat like your grandmother's clothes iron. That it is so
small, it automatically removes it from concerns of being too big to
qualify as lumped components (I will bet the current into the coil
nearly equals the current into its other end).

Some claims bandied here would have us believe that its "high Q"
renders an efficiency (per unit length) unparalleled since the days of
Watt's steam engine. It must certainly be competitive with italian eh
models and show more gain than a Georgia AM station converted to cfa
(but only for the first 300 yards).

If none of this satisfies your quest for understanding; then you can,
of course, visit the vendor's site, observe their "how it works"
description and then find the exact same wording in an unbiased review
from 1996. ;-)

73's
Richard Clark, KB7QHC

Today at the local
hamfest I ran across a 20 meter Isotron that the seller touting.
Anyone really know the theory
behind these things?

As far as I can tell the Isotron is a parallel tuned circuit. On 20M it
should work as well as any other antenna of the same size and height above
ground, cause it depends on feed line radiation, just like all the other
"small' antennas. On 20 it should do ok, but try one on 80 or 160M.

I would not put a 20M Isotron on the air if someone gave me one. There are
too many other ways to get out a decent signal. I might take it apart and use
the aluminum plates, PVC, and wire on a later project, though.

73 Gary N4AST

I don't think the parts are worth $5.00 purchased retail.

Hank
"JGBOYLES" wrote in message
...
Today at the local
hamfest I ran across a 20 meter Isotron that the seller touting.
Anyone really know the theory
behind these things?

As far as I can tell the Isotron is a parallel tuned circuit. On 20M it
should work as well as any other antenna of the same size and height above
ground, cause it depends on feed line radiation, just like all the other
"small' antennas. On 20 it should do ok, but try one on 80 or 160M.

I would not put a 20M Isotron on the air if someone gave me one. There
are
too many other ways to get out a decent signal. I might take it apart and
use
the aluminum plates, PVC, and wire on a later project, though.

73 Gary N4AST

I don't think the parts are worth $5.00 purchased retail.

I agree Hank, if you want something small and cheap on 20M, lots of
alternatives.
73 Gary N4AST

The theory has been worked out for the last 100 years and your Isotron will
work exactly as the theory predicts.

Radiated power will be about 1 watt and the antenna itself will glow in the
dark.

I'm surprised you backward Yanks still believe sales blurbs. In Europe we
have what are known as "The Trades Description Acts" (Of parliament).
----
Reg.

Reg

Yanks started on snake oil in the old west and can't break the habit. I'm a
Canuck and didn't get as exposed! But a little more info would be
appreciated. Also I'm wondering if the angle of the dangle on the Isotron
is important, hi..hi..
73
Hank WD5JFR
"Reg Edwards" wrote in message
...
The theory has been worked out for the last 100 years and your Isotron
will
work exactly as the theory predicts.

Radiated power will be about 1 watt and the antenna itself will glow in
the
dark.

I'm surprised you backward Yanks still believe sales blurbs. In Europe we
have what are known as "The Trades Description Acts" (Of parliament).
----
Reg.

That is probably like our "truth in advertising" laws. They are on the books
but poorly enforced. It is, in most cases up to the consumer to enforce
these laws by lawsuit.

"Reg Edwards" wrote in message
...
In Europe we
have what are known as "The Trades Description Acts" (Of parliament).
----
Reg.

Hank,
I had one for 10 meters and it worked as well as any
generic 1/4 wave, sort of. Not my first choice, but if
you need an unobtrusive antenna, it works, and it's
better than nothing. Don't know about the 20 meter one,
but the 10 meter Isotron was a real P.I.T.A. to tune.
'Doc

PS - The thing about 'snake oil', most of it contained
alcohol. Drink enough of it and who cares if it works
or not...

UK Trade Description Act, 1968.

It is an offence for a trader to apply a false or misleading description to
goods. (Note it is the trader, not the manufacturer, who is involved.)

All goods are covered except houses.

The local (the Council) Trading Standard Authorities are under a statutary
duty to enforce the act. The local Trading Standards Officer has powers of
entry, inspection and seizure of goods.

It is not the job of the Authority to obtain compensation for the offence
but to take steps necessary to prevent others from being deceived such as
confiscation of goods from shops.

It is up to the purchaser to take action in the civil courts for
compensation. With the support of the Authority he will very likely succeed.

But for the sake of a falsely-described, $10, second-hand radio antenna is
it worth the trouble?

The Trading Standards Officer would have to engage the services of
consultant radio engineers to conduct prolonged and expensive field trials
in order to prove the point.

A court of law would not accept a mere statement of Maxwells equations or
any of Terman's or Kraus's learned dissertations. A bewigged judge, of
course, would be well advised to seek the opinions to be found on this
newsgroup.
----
Reg, G4FGQ

I've just had a look in Google at the manufacturer's so-called specification
for the Isotron.

Very carefully, nothing is said which could cause dispute.

But there's no mention of by-far the most important characteristic -
radiating efficiency!

There's no law against NOT mentioning anything. This is precisely where the
manufacturer/trader has the advantage over a prospective gullible ignorant
customer.

Quality is a measure of conformance to the intended (as specified and
agreed) purpose.

If a buyer with a fistful of cash doesn't know what he wants he can't
complain if he doesn't get it.
----
Reg.

Reg Edwards wrote:

I've just had a look in Google at the manufacturer's so-called specification
for the Isotron.

Very carefully, nothing is said which could cause dispute.

But there's no mention of by-far the most important characteristic -
radiating efficiency!

There's no law against NOT mentioning anything. This is precisely where the
manufacturer/trader has the advantage over a prospective gullible ignorant
customer.


Unfortunately, the enthusiastic ham, most of whom have only a rudimentary
knowledge of antennas, is always looking for something that will help him
get his signal out. It is not so much that he is gullible or ignorant, but
desires to get his signal on the air in the easiest way possible. I've been
hamming since 58, spent my whole navy career in communications and electronics,
and after retiring became a journeyman technician -- and I am often tempted
to try some of these gadgets. Thanks to rec.radio.amateur.antenna I have
learned enough to know what is worth trying, and what is not.

Irv VE6BP




--
--------------------------------------
Diagnosed Type II Diabetes March 5 2001
Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
--------------------------------------
Visit my HomePage at http://members.shaw.ca/finkirv/
Visit my very special website at http://members.shaw.ca/finkirv4/
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--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Henry Koleanik, WD5JFR wrote:
"Anyone really know theory behind these things?"

The Isotron is a small tuned loop. Tuning gets rid of reactance which
would cripple performance were it not removed from the loop.

A small loop has a null perpendicular to the plane of the loop. Energy
suppressed in directions of the loop`s axis is radiated in the plane of
the loop giving a directivity power gain of about 1.5 (not dB, where
it`s just under 2 dB gain) over an isotropic radiation in the plane of
the loop as in other directions as well.

The bad news is that even made with a large surface area, the small
loop`s loss resistance looms large as compared its radiation resistance.

The 3rd edition of Kraus` "Antennas" is a clear source of single-turn
circular loop information. Fig.7-10 on page 209 gives radiation
resistance versus loop circumference. Fig. 7-11 gives directivity.

If radiation resistance were 0.5 ohm and r-f resistance were 0.5 ohm,
efficiency would be:
0.5/1=50%

Kraus has Fig. 7-17 on page 217 which gives radiation efficiency as a
function of frequency for a 1-m-diameter single-turn 10mm copper tubing
loop in air. At 1 MHz, the loss is about 40 dB. At 10 MHz, the loss is
about 6 dB. The radiation resistance of the loop is rising more rapidly
than is the loss resistance as frequency goes up. The loss is enormous.
This is ok for reception in most cases, but it`s very dear for
transmitting.

Best regards, Richard Harrison, KB5WZI

Thanks, I'll dig out Kraus..
Hank
"Richard Harrison" wrote in message
...
Henry Koleanik, WD5JFR wrote:
"Anyone really know theory behind these things?"

The Isotron is a small tuned loop. Tuning gets rid of reactance which
would cripple performance were it not removed from the loop.

A small loop has a null perpendicular to the plane of the loop. Energy
suppressed in directions of the loop`s axis is radiated in the plane of
the loop giving a directivity power gain of about 1.5 (not dB, where
it`s just under 2 dB gain) over an isotropic radiation in the plane of
the loop as in other directions as well.

The bad news is that even made with a large surface area, the small
loop`s loss resistance looms large as compared its radiation resistance.

The 3rd edition of Kraus` "Antennas" is a clear source of single-turn
circular loop information. Fig.7-10 on page 209 gives radiation
resistance versus loop circumference. Fig. 7-11 gives directivity.

If radiation resistance were 0.5 ohm and r-f resistance were 0.5 ohm,
efficiency would be:
0.5/1=50%

Kraus has Fig. 7-17 on page 217 which gives radiation efficiency as a
function of frequency for a 1-m-diameter single-turn 10mm copper tubing
loop in air. At 1 MHz, the loss is about 40 dB. At 10 MHz, the loss is
about 6 dB. The radiation resistance of the loop is rising more rapidly
than is the loss resistance as frequency goes up. The loss is enormous.
This is ok for reception in most cases, but it`s very dear for
transmitting.

Best regards, Richard Harrison, KB5WZI

Richard,

I think you are confusing the Isotron by Bilial with the Isoloop
formarly made by AEA. The Isoloop was a small loop antenna tuned with
a large remote variable capacitor like you describe. The Isotron is
just a large fixed capacitor (you can make a slight manual tune to it,
not remote tune like a magloop) and a muliturn solenoid inductor. I
serves as nothing more than a lossy load to dump your power into. The
actual antenna is the metal mast you are supposed to attach the
Isotron to. The antenna is essetially a small radom wire antenna
composed of the metal mast and/or the outside shield of the coax
attached. Whatever power is not lost in the Isotron, travels on the
metal mast and outside shield of the coax and couples into your house
wiring, television and neighbors appliances, and oh yes, a small
amount is radiated. It works essetially the same as the supposed
cross field and eh antenna. A large LC tank connected to a short
random wire antenna composed of the ground lead and outside of the
coax shield. If you choke off the current from the ground lead and
outside coax shield, you essentially have an unshielded dummy load.
Thats all there is to them.

73,
Dan

(Richard Harrison) wrote in message ...
Henry Koleanik, WD5JFR wrote:
"Anyone really know theory behind these things?"

The Isotron is a small tuned loop. Tuning gets rid of reactance which
would cripple performance were it not removed from the loop.

A small loop has a null perpendicular to the plane of the loop. Energy
suppressed in directions of the loop`s axis is radiated in the plane of
the loop giving a directivity power gain of about 1.5 (not dB, where
it`s just under 2 dB gain) over an isotropic radiation in the plane of
the loop as in other directions as well.

The bad news is that even made with a large surface area, the small
loop`s loss resistance looms large as compared its radiation resistance.

The 3rd edition of Kraus` "Antennas" is a clear source of single-turn
circular loop information. Fig.7-10 on page 209 gives radiation
resistance versus loop circumference. Fig. 7-11 gives directivity.

If radiation resistance were 0.5 ohm and r-f resistance were 0.5 ohm,
efficiency would be:
0.5/1=50%

Kraus has Fig. 7-17 on page 217 which gives radiation efficiency as a
function of frequency for a 1-m-diameter single-turn 10mm copper tubing
loop in air. At 1 MHz, the loss is about 40 dB. At 10 MHz, the loss is
about 6 dB. The radiation resistance of the loop is rising more rapidly
than is the loss resistance as frequency goes up. The loss is enormous.
This is ok for reception in most cases, but it`s very dear for
transmitting.

Best regards, Richard Harrison, KB5WZI

Dan, WK8L wrote:
"I think you are confusing the Isotron by Bilal with the Isoloop
formerly made by AEA."

I apologize for causing confusion. The Isotron is only a large capacitor
with a trimmer?

A large capacitor has a low reactance and to form a resonant circuit.
must be paired with an equally low reactance of the inductive variety. A
small rod or a small loop, in terms of wavelength, have similarities.

Terman is much more eloquent than I so I`ll quote from page 907 of his
1955 edition:
"The directional pattern is independent of the exact shape of the loop,
provided the loop is small compared with a wavelength.

The directional pattern of a small loop is identical with that of an
elementary doublet. The only difference is that the electric and
magnetic fields are interchanged. For this reason a small loop is often
called a magnetic
doublet.

The radiation resistance of a loop antenna is less the smaller the loop
area. For the radiation resistance to be large enough to give good
antenna efficiency, it is necessary that the loop perimeter be of the
order of a wavelength."

So the name "magloop" may come from "magnetic doublet". When is a loop
small enough to be a 'magloop"? One requirement may be the same current
in all sides of the loop and I`ve seen that specified as a perimeter of
0.1 wavelength or less. Like many specifications it may be arbitrary.

I suppose calling a capacitor an "Isotron" is arbitrary too.

Best regards, Richard Harrison, KB5WZI

In article ,
Richard Harrison wrote:

I apologize for causing confusion. The Isotron is only a large capacitor
with a trimmer?

Well, from what I can see of it (based on the diagrams on the Web), it
looks rather as if it's intended to behave like a very short dipole.
It's center-loaded and resonated with a large coil, and has a really
humongous capacity hat (the plates). The center coil, and the short
conductors leading from the top and bottom of the coil to the two
capacity-hat plates, would do the radiating.

If this is a correct description, then I'd expect the Isotron to
suffer from the same limitations as any short, loaded dipole - a low
radiation resistance (perhaps only an ohm or two) and a relatively
high loss resistance. Used in isolation (e.g. on an ungrounded mast,
with a choke on the feedline) its efficiency would be quite poor.

The fact that it's stated that it _must_ be grounded to a metal mast
for proper operation raises a big red flag (in my own humble view, at
least). This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.

It's even possible that in this configuration, the antenna system does
its best radiating when the Isotron itself is tuned _away_ from a good
match with the feedline, thus forcing significant currents onto the
feedline and the mast. One might (in this case) even view the Isotron
assembly as being something akin to a transmatch, with its reactivity
matching the impedance of the "antenna" (the mast and feedline) to the
feedline.

It'd be quite interesting to have somebody set up an Isotron as
directed, tune it to get the best signal in and out, and then run an
RF current meter over the mast, mast-grounding wire, and feedline when
transmitting. If there are relatively high currents present on
these conductors, it'd certainly be diagnostic!

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.
============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

On Tue, 23 Mar 2004 19:44:47 +0000 (UTC), "Reg Edwards"
wrote:
What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

It's like promoting your SUV enjoying 80 MPG (but failing to disclose
that is with a 100 MPH tailwind).

Reg Edwards wrote:
What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

Maybe for an Isotron, but not for a beam.
--
73, Cecil http://www.qsl.net/w5dxp



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"Reg Edwards" wrote in message
...
This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.
============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

If I have a nice yagi array aimed at the moon and thus a low system noise
temp, and the feedline is allowed to radiate, I would think that might have
a bit of an effect not only on the array's pattern but also ruin the system
noise temp. The return loss then is also a function of cable length, routing
etc. Hardly a predictable array.
I can think of other examples. Although I admit in the case of the Isotron,
cable radiation is probably an advantage.

Dale W4OP

Reg Edwards wrote:
This suggests that other folks are correct in asserting that

the mast, and the outside of the feedline are doing a lot of the
radiating.

============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.



If your interest is to spray your rf all over the place then a radiating
feedline is really FB.

If you have a $1500 tower, a $600 rotator, a $800 beam, a $3000
amplifier all connected to a $3000 transceiver, then you really want to
steer your RF in a controlled direction. Under these conditions a
radiating feedline destroys the nature of the antenna pattern and you're
not getting what you paid for.

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

Maybe for an Isotron, but not for a beam.

Or in cases where radiation coming off of the feedline would be
inconvenient for other reasons - e.g. the feedline runs in close
proximity to other wiring (RFI and telephone interference, or signals
getting where they don't belong in a multi-repeater shared site), or
metal pipes or metal-loaded walls (e.g. stucco).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Steve Silverwood wrote:

Just for the record, Hank, I've had an Isotron antenna and it works just
like a very expensive dummy load. Provides a good SWR match but doesn't
radiate worth a darn, and it's deaf as a post for receive.

"But look at that beautiful plumage!"

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Dave Platt" wrote in message
...
In article ,
Steve Silverwood wrote:

Just for the record, Hank, I've had an Isotron antenna and it works just
like a very expensive dummy load. Provides a good SWR match but doesn't
radiate worth a darn, and it's deaf as a post for receive.

"But look at that beautiful plumage!"

It's "pinin' for the fjiords"...
__
Steve
KI5YG
..

Just for the record, Hank, I've had an Isotron antenna and it works just
like a very expensive dummy load. Provides a good SWR match but doesn't
radiate worth a darn, and it's deaf as a post for receive.

====================================

But that's exactly how it's supposed to work although the manufacturer
doesn't mention it in his specification.

And as every good amateur knows, the most important characteristic of any
antenna is the ubiquitous SWR. The ARRL and RSGB handbooks attach much
space to it.

"Reg Edwards" wrote in message ...
Just for the record, Hank, I've had an Isotron antenna and it works just
like a very expensive dummy load. Provides a good SWR match but doesn't
radiate worth a darn, and it's deaf as a post for receive.

====================================

But that's exactly how it's supposed to work although the manufacturer
doesn't mention it in his specification.

And as every good amateur knows, the most important characteristic of any
antenna is the ubiquitous SWR. The ARRL and RSGB handbooks attach much
space to it.

Also, a catchy name like "Isotron" helps...Sounds like some kind of
ray gun from a cheap 1950's sci-fi thriller...The combination of the
catchy name, and the low SWR, insure mo-tricity. :/ MK

Mark Keith wrote:
Also, a catchy name like "Isotron" helps...Sounds like some kind of
ray gun from a cheap 1950's sci-fi thriller...

Like the "Interositer" from "This Island Earth"?
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Mark Keith wrote:
Also, a catchy name like "Isotron" helps...Sounds like some kind of
ray gun from a cheap 1950's sci-fi thriller...

Like the "Interositer" from "This Island Earth"?

The interositer worked..

The interositer worked..

It sure did, almost got that guy and gal killed by aliens. That thing was like
a giant Heathkit from outer space. I envied the guy in the movie getting to
put it together.
73 Gary N4AST