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Author Topic: Isotron ant and QRP? Has anybody experience to sha  (Read 3696 times)

Posts: 79

« on: October 05, 2002, 09:52:31 AM »

After reading favourable reviews on this website, I wonder if some QRPer has used this antenna and wlt share his impressions. Thank you. Chris

Posts: 17477

« Reply #1 on: October 07, 2002, 04:01:09 PM »

In my experience, the Isotron 40m antenna would be a
great way to introduce newcomers to QRP:  if they run
100 watts into it, they will probably have a good
experience of what it is like to operate QRP!!!

And, of course, QRP'ers know that it is possible to get
great signal reports running low power, so the same is
true of an inefficient antenna when running higher

Again, from my experience, it appeared that the main
source of radiation was the outside of coax cable
itself (and/or the metal mast to which the Isotron is
mounted).  This makes performance highly variable on
the specifics of an individual installation (including
the length of the coax, height of the antenna, mast
material, whether or not it is grounded, etc.)  If you
can put it up 30' on a tower with 50' of feedline
running back to the radio, it may work pretty well:
perhaps about as well as a 50' wire tied off at 30' on
your tower.

Posts: 21764

« Reply #2 on: October 07, 2002, 04:48:50 PM »

When I look at the Isotron, at least the 20m, 30m and 40m models, it's starting to look more and more like an "E-H" antenna (see article on this subject, under  From the experience I've garnered over the past few days, that's a good thing, and a bad thing, depending on your point of view.

(I just "Posted" a comment re the E-H antenna under "Antenna Restrictions" Forum on this site.)

As I found with the E-H, it's 20-30 dB down from my "full sized" vertical, which at first blush sounds horrendous.  However, to its credit, or maybe to mine (good operator!), I used the little 20m E-H antenna for a couple of hours this past weekend, and had absolutely no problem making contacts...including one with Zambia, a country I've rarely worked before, early on Sunday morning, on CW.  The fact that there was "no competition" for this contact made a lot of difference -- in a contest situation, with 200 guys calling him, I probably could not have made the contact.  But it was 7:50am on Sunday, and the Left Coast must have all been sleeping, I got right through.

Try the Isotron, it might surprise you!  However, you could also homebrew an E-H antenna for about $20 and have what appears to be something quite similar...


Posts: 14491

« Reply #3 on: October 19, 2002, 03:51:17 PM »

WB6BYU makes a good point. If I can work a DX station with a good antenna and 1 watt then I should be able to do it while running 100 watts to an antenna that is only 1% efficient. On the other hand, if I'm starting out at only 1 watt then I'm effectivly only radiating 100 mW. In general, QRP and an inefficient antenna is not a good combination.

When you start hearing reports about how great some of the small antennas are, be sure and find out what band was used. An antenna that is pretty inefficient at 75 or 40 meters can be much better on 10 meters.

Bob  AA4PB
Garrisonville, VA

Posts: 11

« Reply #4 on: October 21, 2002, 03:18:07 AM »

I notice that two of the posts really talk bad about the antenna but no where in their posts do I see where they have actually owned or used one.  I'm not even sure they have ever seen one.  All the reviews I have seen from people who actually own one are positive.  I live in an area with heavy restrictions and have ordered one for myself.

Posts: 21764

« Reply #5 on: October 21, 2002, 06:37:13 PM »

NC5C, I have owned the Isotron-20 (20 meter model) for seven years and do occasionally use it for portable camping outings and such.  I've made a great many contacts with it, although my MFJ Super Hi-Q Loop model MFJ-1786, which is no larger (and, in fact, is actually smaller) than the Isotron makes more contacts, more easily, and hears better as well.

Having said that, I was the one who recommended the original poster try an "E-H Antenna," because all the plans and diagrams to do so are public domain and have been published on the internet for some time, and the E-H appears to work about the same as an Isotron, while costing less.  A 20m E-H can be homebrewed for about $20, is somewhat smaller and lighter than the Isotron, and works the same in principle (and in reality, as far as I can tell, since I've been testing an E-H for 3 weeks now).


Posts: 13

« Reply #6 on: October 22, 2002, 04:07:19 PM »

I have been using an 80m Isotron occasionally with a PSK80 Warbler w/ 2 watts output. The Isotron is mounted on my deck rail, about 10 feet off the ground, fed with about 50 ft of RG58. Best DX so far is about 700 miles. Not much to brag about, but useful for local and mde-range QSOs.

Posts: 290

« Reply #7 on: October 30, 2002, 08:02:08 PM »

I once owned the 40/80 meter Isotron combo and found they worked very well for my particular needs at the time.  I was doing consulting work two weeks a month near Rochester, NY between 1996 and 1999. I always stayed at the same place, which was owned by our client, and got permission to mount this antenna.  My bedroom was on the second floor and had a small balcony with a wooden railing.  I mounted the Isotrons on a 10' RS mast and fed it with 25' of RG-58.  The mast was grounded to an outside water pipe at ground level, 10 feet directly below the balcony.  With my rig, an IC-706 and 100 watts, I was able to work Germany in the 75 meter SSB DX window (have the QSL card to prove it) and talked pretty much all over the Eastern 2/3 of the US.  On Forty meters, at night, I regularly kept schedules with friends in Florida, Ohio, Indiana and Kentucky.  At first, I was very skeptical about the size of these antennas, but after talking to several stations who were using them, I figured I would give them a try.  I was satisfied with their performance as they allowed me to get on HF at my restricted portable QTH.

Tom, KR4BD
Lexington, KY

Posts: 17477

« Reply #8 on: October 31, 2002, 04:35:55 PM »


My comments are based on using a 40m Isotron, which is
why I used the phrase, "In my experience...".  I tried
it with different feedline lengths and mounting
methods, and it never seemed to work very well.  True
there might be installations where it works better, but
in my case I would estimate that signals were, at best,
20 dB down from a dipole.

However, I always encourage people to do their own
experiments instead of relying on what others tell
them, and this goes for my own comments as well.  We
will be interested in your experiences with the

If you want to verify my theory that the feedline
is a major contributor to the radiation, make a coiled
coax choke at the feedpoint and see if it changes the
tuning and/or performance of the antenna.  (This will
partly depend on the mast it is mounted on.)

(I found that I could not get ANY indication of
resonance with an MFJ SWR analyzer through a short
coax jumper, even when it was mounted on a metal mast.
The results were quite different with a longer length
of coax.)

Radiation from the coax is not automatically "bad", it
just helps to explain how the antenna actually works.
It also helps to explain why different installations
can have very different results.

The original poster asked for feedback from QRP'ers
who had used an Isotron.  Since I qualified on both
counts, I felt it was appropriate to reply, even
though my experiences were negative.

- Dale WB6BYU

Posts: 6

« Reply #9 on: November 16, 2002, 08:32:27 PM »

I have both the 80 meter and 160 meter Isotrons mounted on a 20 ft. mast fed with 50 ft. of RG-213.
The antennas are adequate, but have limitations in that the bandwidth is very narrow. If you understand their limitations, they are functional. Compared to a longwire or dipole (which I have done side by side comparisons with) they do not perform as well as the wire antennas on transmit or rcv. I have my Isotrons adjusted for favorite segments of the CW portions of the bands and use them for dedicated CW rigs. When you get your Isotron up put a dipole up too and do your own comparisons. When band conditions are good almost any antenna will make contacts. It is when conditions are less than optimal that an antenna's limitations start to show. Have Fun. 73.

Posts: 54

« Reply #10 on: January 09, 2003, 09:41:31 AM »

I live in a townhouse condo with pretty strict CC&R's regarding outside antennas. To get on the air quickly (while I studied how I might put up an 'invisible' antenna Wink I purchased a 20 mtr Isotron.

My shack is on the 2nd floor in the guest bedroom. I mounted the Isotron on an attic support stud and fed it with 25' of good quality coax. One thing about the Isotron, it takes some tweeking to get it working properly so it took me more than a few tries climbing in/out of the attic with my Autek RF-1 to get it tuned. However, after that I had very little trouble making contacts in N & S America.

Lots of people are negative about the Isotron. However, it's easy to discount something like the Isotron if you aren't otherwise restricted in what you can have for an antenna.  True, it ain't no monobeam @ 60' so don't expect the same performance you would get from a 'real' antenna. And truthfully, if you CAN put up a 'real' antenna do so.  

However, for anyone that is severely restricted as to what kind of antenna they can have (if any), the Isotron can be a little miracle and mean the difference between being on the air or not.  

Posts: 13

« Reply #11 on: January 15, 2003, 08:41:26 AM »

I've recently learned something about the operation of the Isotron antenna that I want to pass along. I'm am using an 80m Isotron with a PSK80 Warbler (2 watts) for occasional PSK31 activity. My Isotron is mounted on a 5 foot metal mast which is bolted to the wooden railing of my deck, about 10 feet above the ground, and fed with 20 feet of RG-58 coax. The mast upon which the Isotron is mounted is grounded to a nearby electrical outlet (which essentially grounds the bottom plate of the Isotron and the end of the coax shield where the coax attaches to the Isotron).  The important point here (the "something" which I've learned) is that the other end of the coax shield (at my rig) must also be grounded in order for the Isotron to work. This became apparent to me recently when I changed the computer that hosted my PSK31 software. I was using a 133 MHz Pentium clone PC (with a metal chassis/enclosure). I recently switched to using a 400 MHz laptop. When I switched to the laptop the Isotron SWR went "through the roof" (it was previously about 2:1 when using the old Pentium system). After thinking about this I realized that the laptop was not grounded. My rig (and thus the rig end of the coax) was previously getting its ground connection through the RS-232 cable and the PC chassis ground. Switching to the laptop provided no such ground path for the rig and coax (the rig is a small PC board in a plastic enclosure, powered by a 12 V wall adapter). I attached a ground cable from the rig (at the coax connector) to a nearby electrical outlet ground and the SWR returned to a reasonable value (about 2:1).

With this current set-up (2 watts of PSK31 and the Isotron on 80m) I am easily able to cover New England, NY, and NJ from my QTH in eastern MA. I have also had contacts as far south as GA and west to Iowa (about 1,000 miles).

All this leads to my next comment regarding those critics of the Isotron who claim that the only reason that the Isotron works is because of feed line radiation. Well, I am hard-pressed to believe that a 20 ft. RG-58 coax feed line that has its shield grounded at both ends (and is mostly laying on the ground) could in fact radiate much, if at all. More unbelievable is the proposition that such a radiating coax could possibly radiate a signal that could be received 1,000 miles away. The Isotron must be doing the radiating.

It may be that the Isotron is not as efficient as an 80m skywire dipole, but the advantage of the Isotron is its small size (24 inches x 16 inches x 5 inches) which allows operation on a band that otherwise would be unavailable due to the larger size of traditional antennas.

Mike -  AB1AW  (ex-KB1GUF)

Posts: 157

« Reply #12 on: August 22, 2003, 12:34:43 PM »

You want a review of an Isotron from some who owned one? Ok, here it is. I had a 6m Isotron set up in my back yard at about 15 feet on a RadShack mast. Heard a XE1 40 over and tried for over an hour to contact him with 100 watts. No luck. Over the course of nearly 2 years zero contacts were made with the Isotron. The anteena was tuned to a SWR of 1.4 or less across the SSB portion of the band. Finally a windstorm took it out. The only thing I miss is the money I dumped into it.


Posts: 6


« Reply #13 on: November 25, 2007, 03:55:01 PM »

I have used the Isotron designed for 80 meters.  It is quite an interesting design looks something like a bird feeder.  I have tried the antenna in several posistions and heights...all i can say positively about this antenna is that it tunes up.  Its performance...its not a performer.  when conditions are favorable like any other hf band i get S9 reports around the country.  But under normal conditions i swear the wind blows the signal around!  although i can be heard as a weak station locally and several hundred miles away its nothing to brag about.  With a good tuner anything can resonate.  i reccomend trying to tune a butter knife before wasting your money on an isotron.  
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