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Author Topic: Curious about Isotron  (Read 4870 times)
KK4AXX
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« on: August 31, 2011, 01:07:15 AM »

Hope not to start a stink, (and no, I'm not planning a purchase), but I am curious about the tiny footprint Isotron antennas.  The curiosity comes simply from never seeing them mentioned, save for one little post that brought them to mind.  Whether they work or not I will leave to those that have tried them and the 'experts'.  I tend to be a sceptic though I enjoy experiment with radiators up in the air... like most of us! Grin

So, what's the scoop?
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W8JI
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« Reply #1 on: August 31, 2011, 03:34:05 AM »

Hope not to start a stink, (and no, I'm not planning a purchase), but I am curious about the tiny footprint Isotron antennas.  The curiosity comes simply from never seeing them mentioned, save for one little post that brought them to mind.  Whether they work or not I will leave to those that have tried them and the 'experts'.  I tend to be a sceptic though I enjoy experiment with radiators up in the air... like most of us! Grin

So, what's the scoop?

There are many antennas and parts of antenna systems made by people who know how to build and sell things, but haven't the faintest clue how they actually work or if they really work as claimed.

The Isotron is just one of many from that mold.

If you read the literature you will see it claims SURFACE area matters, and that the Isotron radiates like a "large antenna" because it has a great deal of surface area. (A similar claim was made in a recent eHam loop antenna article, so this is a very common false claim.)

Radiation comes from RF current moving over a linear distance of space. Radiation is all about ampere-feet of linear spatial distance, not surface area. Don't walk, RUN away from anyone telling you that surface area determines radiation characteristics of anything but a geometric collimator of some type (i.e. dish, fresnel lens, or screen reflector). For simple antennas, surface area or conductor length packed in a given volume of space is unrelated to radition effects. It is always all about linear length across an area of space and how current is distributed across that area.

The Isotron actually works because the large plates act like capacitors. The coax comes up in the middle, but will never be symmetrically placed in the electric field between the capacitor plates. This excites the coax shield through displacement currents, and the coax shield acts as an antenna. Since the coax is long, it does not take many amperes of common mode to have a realitively large number of ampere-feet.

So in reality it is a simple end-loading system to make the coax radiate.

Now if you should happen to perfectly balance the e-field and isolate the coax, it would still radiate a little bit. It would act like a very very short end-loaded dipole. The spatial distance is very small, so to radite the same power the amperes would need to greatly increase.  But in most cases the coax will have many times the radiation, from common mode, and the thing that is called the antenna really just helps the coupling that drives the coax.

By the way, this is typical for many small antennas. The EH antenna and the CFA antenna are two other systems that cause the coax to radiate, and there are more. If you installed an Isotron, EH antenna, or CFA antenna up on a 100 foot pole with the feeder running down the pole, all three could work with a signal very much like produced by a 100 foot vertical.  :-)

73 Tom
« Last Edit: August 31, 2011, 03:44:28 AM by W8JI » Logged
AC4RD
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« Reply #2 on: August 31, 2011, 04:07:44 AM »

There has been a LOT of discussion of this here on eham; doing a bit of browsing will turn up a great many comments about the Isotrons.   I believe they're in the "Reviews" section, too.
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KG4RUL
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« Reply #3 on: August 31, 2011, 05:28:20 AM »

Based on personal experience with an Isotron, I can safely say that it radiates about as well as the coax that is connected to it.  If it is the ONLY antenna that you can use, then it WILL get you some contacts.
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KI4SDY
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« Reply #4 on: August 31, 2011, 05:47:56 AM »

You could do a lot better spending a lot less with just a simple dipole wire antenna.  Wink
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K8AXW
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« Reply #5 on: August 31, 2011, 09:37:09 AM »

JI: Thanks Tom for this explanation.  I saw the Isotron advertised in QST recently, once again.  Also, once again, I dismissed this antenna/ad as a "gimmick" but have always wondered if it did work and if so, how well.

I recall an antenna advertisement in QST many years ago for what looked like a dipole antenna with loading coils at the ends.  Apparently someone bought one and tore it apart and found that the "loading coils" were a clump of resistors. The ARRL pulled the ad immediately.

Sometime later, a friend bought a B&W inverted V antenna which looked like the above mentioned antenna.  I had my physician brother-in-law have it X-rayed at the local hospital and found that the 'lumps' at the ends of the wires were full of resistors.

I wrote the ARRL about this and was ignored and last time I checked, B&W was still selling it.

I guess the bottom line of this little dissertation is, if a company says it quacks like a duck and walks like a duck but looks like a turkey,  it probably is a turkey!
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KD0NFY
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« Reply #6 on: August 31, 2011, 10:08:04 AM »

If surface area is what matters, I'm going to make an antenna out of old heat sinks.  8000 db of gain!
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W8JI
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« Reply #7 on: August 31, 2011, 10:08:28 AM »

I think in many cases, the "fraud" is totally unintentional.

In the case of the company in Florida, they had to know they were lying. They were actually chopping up pieces of PC board with IC's and gluing them in the box with the IC's exposed, so people would assume the IC did something. They also had "tuning times" published. The ARRL had no way around pulling their ads.

In the case of resistor loaded antennas, things like the EH or CFA, and several of the small Ham antennas it really is a case of the "inventors" kidding themselves. They make bad measurements, use or invent bad theory, and convince themselves they are telling the whole factual story.

I was around when the resistor loaded folded dipole stuff was first being played with, and knew the original fellow involved who sold the design to the long time vendor. I actually made some load measurements, and knew about 30 years ago how it really worked because I measured heat in a load on an identical antenna. The "inventor" was a nice guy and a good friend, but he really was clueless about how things worked. He was very enthusiastic and always copying or thinking up stuff, but everything was just like magic for him.

Most things that are bad ideas, like helically loaded magnetic loops on through the EH and CFA antennas and such, start out as well-intentioned experiments or ideas. The inventors then close off any critical comments, sort through tests to find anything remotely supporting their claims (usually through a series of bad measurements or useless comparisons), and then stay on their unintentionally misguided path because they have fooled themselves into thinking they invented something.

I'm not sure whose responsibility it is to protect buyers or experimenters from unintentional but very false claims. They are far more common than most people think. It's a fine line between hurting people who may be nice people but making mistakes, people who just refuse to admit mistakes, and intentional fraud.

73 Tom
« Last Edit: August 31, 2011, 10:11:46 AM by W8JI » Logged
AE4RV
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« Reply #8 on: August 31, 2011, 12:22:23 PM »

I've no personal experience with Isotron antennas and they are pretty widely disparaged but for what it's worth, there's a guy in West Virgina who is very active with an indoor Isotron and a QRP rig. He gets a good bit of DX, too. I worked him myself a few months ago.

http://n8zyaradioblog.blogspot.com/
« Last Edit: August 31, 2011, 12:25:36 PM by AE4RV » Logged
W3LK
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« Reply #9 on: August 31, 2011, 12:27:25 PM »


Sometime later, a friend bought a B&W inverted V antenna which looked like the above mentioned antenna.  I had my physician brother-in-law have it X-rayed at the local hospital and found that the 'lumps' at the ends of the wires were full of resistors.

I wrote the ARRL about this and was ignored and last time I checked, B&W was still selling it.

The only wire antenna B&W is currently selling is their Terminated Folded Dipole. It is a legitimate antenna design and has beeen around for years.There is nothing at the ends except the supports for the wire. There IS a resister in the junction of the where the ends fold back, but this is well known, well documented, and B&W doesn't hide the fact. No attempt at fraud, no attempt at anything nefarious. It's the way all such antennas work and there are hundreds (if not thousands) in use by the military and MARS stations. I have one in my back yard.
« Last Edit: August 31, 2011, 12:30:37 PM by W3LK » Logged

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G3RZP
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« Reply #10 on: August 31, 2011, 12:30:39 PM »

In about 1948 or so, there were articles by Wheeler and Chu in what was then the IRE journals about the Q, efficiency and so on of small antennas. As far as I am aware, nobody has ever proved them wrong - even Professor Hately with his CFA.
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W8JI
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« Reply #11 on: August 31, 2011, 12:46:15 PM »

I've no personal experience with Isotron antennas and they are pretty widely disparaged but for what it's worth, there's a guy in West Virgina who is very active with an indoor Isotron and a QRP rig. He gets a good bit of DX, too. I worked him myself a few months ago.

http://n8zyaradioblog.blogspot.com/


No offense, but this style of example is the number one defense of incorrect antenna technical claims.

I can work Japan on 160 meters from my mobile from here in Georgia, and easily work VK's on 160 with that antenna. It is less than 1% efficient. On 40, I can work VK longpath and often break through pileups ahead of other stations.  I could invent some wild pie in the sky claims, write some blathering about surface area, but I know what the efficiency is.

Almost anything will make contacts, and with enough patience and time and being in the right place I could easily have DXCC on 80-10 with a very poor antenna.

Everyone should know almost anything can make contacts, and make some people happy.  This doesn't mean at all that an antenna works as described or claimed.

Understand disagreeing with false claims is nothing like saying no one will ever be happy with the contacts they make.
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G8HQP
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« Reply #12 on: August 31, 2011, 12:58:09 PM »

There may be a small advantage from more surface area. Not better radiation, but broader bandwidth. The more closely an antenna fills the 'Chu-Wheeler sphere', the more closely can it approach their limit (roughly speaking). This of course does not apply to 'antennas' which rely on feeder radiation, as these are just bits of wire. On the other hand, an 'antenna' which works by inducing secondary currents in surrounding items (so it is actually just an exciter/primary, with the surroundings doing the real radiation) might appear to do better than Chu-Wheeler.
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W8JI
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« Reply #13 on: August 31, 2011, 03:21:26 PM »

There may be a small advantage from more surface area. Not better radiation, but broader bandwidth. The more closely an antenna fills the 'Chu-Wheeler sphere', the more closely can it approach their limit (roughly speaking). This of course does not apply to 'antennas' which rely on feeder radiation, as these are just bits of wire. On the other hand, an 'antenna' which works by inducing secondary currents in surrounding items (so it is actually just an exciter/primary, with the surroundings doing the real radiation) might appear to do better than Chu-Wheeler.

Actually more surface area can reduce resistance and resistive losses, but that goes without saying. Bandwidth in a very small antenna is more proportional to stored energy, the ratio of dissipative (including EM radiation) resistance to reactances, than conductor widths.

Conductor widths, as you are using, apply to large antennas. A wide area where electric fields are strong can reduce the electric field concentration by spreading the boundary area out. Less concentrated fields reduce energy storage or Q.

More surface area does not mean more bandwidth unless it also reduces stored energy.

What Isotron claimed, the last time I read their site, was the wide surface area made it act like a full size antenna because it has the same surface area as a full size antenna. This is the same nonsense the helically wound loop used.

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K0CWO
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« Reply #14 on: August 31, 2011, 05:46:34 PM »

There is no substitute for cubic inches.  It is hard to beat 234/468 math when it comes to RF. Shocked
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