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Author Topic: Isotron antennas  (Read 735 times)
W3JJH
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« on: July 19, 2004, 09:44:46 AM »

ANY antenna that is small compared to a wavelength will radiate equally poorly in all directions.  It will be omnidirectional because it approximates a point source.  It will radiate poorly because its radiation resistance (output impedance, if you will) is badly matched to the characteristic impedance of free space.

As Scotty told the Captain"  "Ye cannae change the Laws of Physics!"
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K7IBC
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« Reply #1 on: July 18, 2004, 07:52:33 PM »

I'd like to get input from users of Isotron antennas both positive and negative.

I am researching different antenna options for my station.  The only information I have come across so far have been the CQ and ARRL articles touted on the Isotron web site.

Thanks a lot.

73 de Pat K7IBC
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KR4BD
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« Reply #2 on: July 18, 2004, 08:05:40 PM »

I had the 40 & 80 meter combo Isotron antennas in portable operation from 1997-1999 in Rochester, NY.  They weren't great, but I had NO ROOM for anything else, so I mounted these antennas on a 10ft mast on a second floor balcony.  I installed them as prescribed (grounding is important) and used an IC-706 (100 watts).  I was able to work regular schedules with friends in the midwest and Florida on 80 and 40 SSB.  I even worked a German station on 3795 kHz with it, so they DO WORK.  I also have a local friend who mounted the 80 meter version on his chimney and regularly loaded a kilowatt (SSB) into his with supposedly good results.  I first learned of these antennas when QSOing with a guy on 40 meters one night and was impressed how well I was hearing him with only 100 watts...  But, you will get better results if you have the room to put up simple dipoles where you live. If you have no other options, I can assure you will get a signal out with these compact antennas.

Tom, KR4BD
Lexington, KY
 
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N6AJR
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« Reply #3 on: July 18, 2004, 10:01:26 PM »

I feel they are better than no antenna at all and actually work better than you would expect, but my favorite is still the fan dipole..

http://www.hamuniverse.com/multidipole.html
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K0RFD
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« Reply #4 on: July 18, 2004, 10:29:05 PM »

This really needs to be an Eham Elmers FAQ.
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K7IBC
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« Reply #5 on: July 18, 2004, 11:06:41 PM »

It probably could qualify as a FAQ, but the answers in an FAQ don't give true personal testimonies and opinions.

Anyway, thanks for the answers thus far.  I am considering the Isotron due to space constrictions.
A dipole would be great, but the yard plot dimensions and the XYL are against it.

73 de Pat K7IBC
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KT8K
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« Reply #6 on: July 19, 2004, 11:51:42 AM »

I'm with Tom W8JI on this.  The isotron is a poor compromise as an antenna, and its performance can be exceeded by (for example) a slinky dipole, a loaded-shortened dipole (even if half or more of its length is taken up in coils), a hamstick dipole, a coil-loaded vertical, etc.

I have a wire antenna and radials for my HF9v all made from 18 gauge magnet wire.  It's brown in color and thin enough that I can't see it easily or sometimes at all looking out my own kitchen window, just 10 or 20 feet away.  I have a horizontal loop of the stuff hanging over the 2nd floor gutters and around the house, extending to the top of a small tree near the back of the house, and I have to look really hard to tell it's there.  It does fine with a tuner on 80-15 meters, and beats my vertical antennas for dx on 10 meters.  Higher would be better, but 18-20 feet is all I can manage at this house.  I'm sure it would beat an Isotron all hollow, though.  

Think stealth, and nearly-invisible wire antennas, and you will be so much better off (and save a lot of $$ too).  If I had a closet as my only space for an antenna I might try a magnetic loop antenna such as the Isotron, but I can't see that ever being the case.

Feel free to contact me if you'd like to discuss your antenna situation in more detail.  Join your local ham club, if you haven't already (search for local clubs by going to www.arrl.org and picking the "clubs" link at the top).  And check out the articles here on eham as well as the popular books on stealth antennas.  You will be pleased with what you can do.

73 & good reception de kt8k - Tim
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W8JI
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« Reply #7 on: July 19, 2004, 07:17:59 AM »

Pat,

It almost seems silly to say it, but a small antenna is a small antenna. None of them will ever work like a large antenna.

The Isotron (I had one given to me at one time) isn't a particularly good small antenna, but you can make contacts with it.

A small MFJ loop antenna I had was about 1-3 S Units stronger than the Isotron with almost anyone I worked. When I'd bet a 579 with the loop, I'd typically get a 559 with the Isotron. A dipole was typically 589-599 in comparison to the loop.

Anything that get's you on the air is a good thing, but you might consider a single thin strealth dipole fed with TV twinlead and a small antenna tuner.

73 Tom
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W5WJP
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« Reply #8 on: July 19, 2004, 08:37:04 PM »

I had a 6m Isotron....waste of money. It could hear fairly well but could not contact anyone....yes 6 was open.

There are more options for "small" antennas.

You could try a dipole made from copper tape, put it up on the eaves, feed it with twin lead and use a tuner. Make the dipole for the lowest frequency you are going to use and with a decent tuner you should be able to work all bands higher. This could even be painted over (non-metallic paint) and will be invisible. The twin lead could even be connected with alligator clips.

For portable QRP use, I use a SuperAntenna mounted on a camera tripod. It works, but it still is a very comprimized antenna.

73,
W5WJP
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K9COX
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« Reply #9 on: July 19, 2004, 11:02:25 PM »

A good friend of mine, WA9PLW, has a full complement of Isotron antennas and also a loaded dipole and a GAP Titan vertical. The dipole is about 80 ft long for 75m and 40m. The Isotrons always compare favorably to the other antennas. Sometimes weaker by an S unit or two and sometimes the same strength or stronger with less QRN. I was skeptical of his claims at first, but have seen it too many times now. He has made me a believer in the Isotrons.
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W8JI
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« Reply #10 on: July 20, 2004, 06:32:24 AM »

by W3JJH on July 19, 2004  Mail this to a friend!  
It will radiate poorly because its radiation resistance (output impedance, if you will) is badly matched to the characteristic impedance of free space.
As Scotty told the Captain" "Ye cannae change the Laws of Physics!">>>

The Laws of Physics don't say anything about "matching the impedance of freespace". That has nothing to do with efficiency.

Spoick always said that "law" comes from Ham Radio Myths about how antennas work, not from science.

73 Tom
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KR4BD
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« Reply #11 on: July 20, 2004, 09:51:45 AM »

I think most of us can agree about the (in)efficiency of the Isotron antennas AND they probably violate every law of physics (and everything else, for that matter).  

The original question was basically:  Do these antennas work?  

The answer is YES.  Many of us who have been in the hobby for a while have decent antenna setups.  When compared to more "traditional" antennas, the Isotrons look like a joke.  In fact, I heard that the ARRL (QST) would not accept Isotron's advertising for many years because they considered them to be some sort of "snake oil" antenna.  All the while, CQ and other magazines ran ads for them.  Well, guess what?  Eventually someone at the ARRL realized these antennas DO WORK and now they gladly accept advertising for them.  

If you live in an antenna restricted area (and such areas are becoming more common every day), the Isotron might offer you your only hope of operating HF.  

Or...If you have no room for anything else, these breadbox sized antennas will certainly get you on-the-air---if you install them properly.  

Tom, KR4BD
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K1CJS
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« Reply #12 on: July 20, 2004, 11:54:51 AM »

I've had some small experiences with these antennae, and I can tell you they do work.  Another ham has his set up include a 20 meter isotron and a 40 meter isotron, and he makes contact after contact, inside and outside the US.

The key to making the isotron antenna work is following the instructions EXACTLY as they are written.  If the instructions say to do something, do it, no matter how hard it may be to do it.  If you bypass or change one item, it greatly impacts the efficiency of the antenna.
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KT8K
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« Reply #13 on: July 20, 2004, 04:32:24 PM »

I looked, and didn't find their instructions to be very specific regarding installation, except to avoid 1/4 wavelength feedlines.  Does that have any relationship to the claim I've read that most of the antenna's radiation comes from the feedline?
curious.  73 de kt8k - Tim
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