Isotron antenna

Once again, the challenge any short antenna system has is efficiency. The Isotron antenna's approach to improved efficiency is to use lower loss components. And since the model 200B does need a radio frequency ground system to work, it is legal under Part 15 for AM.

The design and construction of amateur radio antennas by Isotron is the same as for the Part 15 model. Essentially, the device is a resonant 50 ohm impedance tank circuit suspended on a support mast.

I have no clue as to the comparison with a base loaded vertical antenna system. However, logic would tell you the ground losses would be remarkably different. Most of the loss in the base loaded vertical is in the ground radial system.

Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.

Rhema Radio - The Word In Worship
AM 1660 - FM 93.5
http://www.rhemaradio.org

Once again, the challenge any short antenna system has is efficiency. The Isotron antenna's approach to improved efficiency is to use lower loss components. And since the model 200B does need a radio frequency ground system to work, it is legal under Part 15 for AM........

Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.

Rhema Radio - The Word In Worship
AM 1660 - FM 93.5
http://www.rhemaradio.org

Has anyone out here used one. I know of some use on amateur radio but much higher in frequency and as one would suspect, the BW is quite sharp. (narrow)

...And since the model 200B does need a radio frequency ground system to work, it is legal under Part 15 for AM.

Did you intend to write "does NOT need" a ground?

In any case, here is a paste from the Isotron website about their MW AM antennas:

Antenna should be mounted on a metal mast with a maximum size of 1.5 inches. The mast can be ground-mounted with guy wires, mounted to a wooden pole, or mounted to a tower leg. Antenna should be mounted as high as possible for best performance.

This suggests that some, or even most of its gain could be supplied by radiation from the conductor and/or metal mast leading to true r-f ground below the surface of the earth.
//

You might want to check out this thread about a guy built his own Isotron antenna. Although it was tricky to tune, he was pleased with the results. There are pictures of the finished antenna and he explains how he built it.

As you know, there aren't many MW antenna designs that eliminate the need for ground radials. The EH antenna is the only other one that comes to mind and, so far, the published results have been inconclusive.

http://www.pcs-electronics.com/phpBB2/viewtopic.php?t=1092

DB52

OOP's. Rich you are correct. The Isotron Part-15 antenna does NOT need a radio frequency ground. And the only way a radio frequency ground would not radiate is if it were a tuned counterpoise. It would be, after all, the hidden and very lossy side of the dipole. My experience has been that all radio transmitting and receiving antenna work against some sort of ground potential. The FCC, however, has for decades encouraged the use of lightning and service ground systems on all transmitters external to the chassis for safety reasons. Practically, that requires a large current carrying conductor to run from the chassis to ground potential. Part 15 does not define what constitutes ground potential. It covers only the added length of the ground lead to the total length of 3 meters or about 9 feet, 9 inches. In the strictest interpretation of Part 15 rules, the Isotron seems to pass muster.

I know several amateur radio folks who have used the 160 meter model antenna from Isotron with reasonable results in comparison with most 1.8 MHz short antennas not mounted a half wave length in the clear. It is a better transmitting antenna than receiving due to the small surface area. The addition of ground radials does not seem to radically improve performance. Drawing parallels to the part 15 model, you probably could expect similar performance.

Not a lot of science here, just on the ground experience and logic.

Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.

Rhema Radio - The Word In Worship
AM 1660 - FM 93.5
http://www.rhemaradio.org

Is there away to couple this to the AMT 1000 without a boat load of mods?

WDCX AM1610 Part 15
John
Owner-Operator-Chief Engineer-Program Manager

The Isotron Part-15 antenna does NOT need a radio frequency ground. And the only way a radio frequency ground would not radiate is if it were a tuned counterpoise. It would be, after all, the hidden and very lossy side of the dipole.

Sorry, but you might want to research this a bit further. A buried r-f ground consisting of radials, ground rods or other conductors, and used with a vertical "monopole" MW radiator only serves as a return path to the tx system for r-f currents induced in the earth by the MW radiator. Not supplying a return path for those currents is similar to connecting something to only one terminal of a battery -- current doesn't flow. And in the case of a Part 15 AM antenna, no/very low r-f current flowing in the antenna system means zero/very poor radiation efficiency.

The buried r-f ground itself produces no useful radiation, but a conductor leading from the buried r-f ground to an elevated Part 15 tx chassis does radiate. Physics shows that the flow of r-f current along an exposed conductor generates that radiation, just as it does when flowing in the 3-meter part of the antennna.

My experience has been that all radio transmitting and receiving antenna work against some sort of ground potential.

Just to note that there are many antenna forms that do not need or use an r-f ground to radiate very efficiently. A 1/2-wave dipole is one example. The antennas on satellites are another. Unfortunately such antennas are not practical for use in the medium wave broadcast band.

In the strictest interpretation of Part 15 rules, the Isotron seems to pass muster.

Only if the installation does not include a radiating conductor length greater than three meters, including the conducting path from the tx chassis to the true r-f ground for the system -- which r-f ground does NOT exist at the top of a large "grounded" conductor/tower/metal flagpole/billboard frame or whatever leading up to the tx from a buried ground, but at the other end of that conductor, where it connects to the buried ground conductors. Again, this is what physics tells us.

Hopefully my post will not be taken as combative, unloading, or being unreasonable simply because it contains information that differs from what prompted my response.

//

Sorry, but you might want to research this a bit further. A buried r-f ground consisting of radials, ground rods or other conductors, and used with a vertical "monopole" MW radiator only serves as a return path to the tx system for r-f currents induced in the earth by the MW radiator. Not supplying a return path for those currents is similar to connecting something to only one terminal of a battery -- current doesn't flow. And in the case of a Part 15 AM antenna, no/very low r-f current flowing in the antenna system means zero/very poor radiation efficiency.

Ok, I'm probably jumping in way over my head here, Rich.. But looking at the schems of the 80 meter version of the antenna in the manual (page 19 of the pdf) at:

http://www.isotronantennas.com/isomn80.pdf

..ok, now that's 3 of them linked together, but it was a place that shows a simple schem of the beastie.. Now it *looks* like electrically it amounts to a sort of physically large tuned tank, somewhat like some of the old loop antennas, though with the parts set up in maybe a different physical arrangement.

Now, with a straight "stick" vertical being fed from a tap on the loading coil and a tuning cap between the base of the coil and the ground, we'd clearly have an "open circuit" if it were not for some of the radiated power returning to the antenna's ground via something like buried radials.

But looking at the Isotron antenna schematics, it looks like a simple series LC "tank", so wouldn't that circuit provide the path for current flow without the ground radial system needed for a standard vertical? I definitely agree that the standard vertical needs the ground return to "make a circuit".. But this looks a bit different from that to me, at least at first glance.

Now the real questions I'd have about the Isotron antenna...

Since a series LC offers zero impedance at resonance, wouldn't a transmitter see the "load" from this thing as basically a short circuit? Like connecting the antenna terminal right to a ground? I suppose the resistance value from the coil winds might prevent that, but it was one of the first thoughts I had.

Also, what affect is the close proximity of the earth going to have in an antenna where the top of it is only 3m off the ground? I could see where this design might be theoretically superb if one was transmitting from say a hot air ballon with it hanging underneath, where one could easilly be a wavelength or more off the ground. But I'd think that in any practical application where it's mounted a few feet or meters above the ground, the earth would act like a capacitor plate, so height could drastically affect tuning?

Also, those capacitor plates are rather large. Could wind on them result in enough vibration to add unintentional modulation sort of like a rather odd and large condenser mic? Or maybe even any loud nearby sound like a truck passing.

As wdcx already mentioned, one would expect the tuning to be a bit touchy and the bandwidth to be pretty narrow. Might be great for cw or something like a 200 hz test tone for a beacon, but would the bandwidth even be usuable for music at a reasonable fidelity?

Sorry if some of those questions are a bit nave, but anybody have any thoughts on any of them?

Daniel

Now it *looks* like electrically it amounts to a sort of physically large tuned tank... etc

What I see when looking at the picture of the Part 15 AM Isotron is a base-loaded, short vertical with additional loading elements (the plates) on the ends of it. The plates might serve to raise the radiation resistance of this electrically short radiator slightly, and reduce the inductance needed in the loading coil.

But a fundamental "given" about antennas is that their efficient radiation requires r-f current to flow over some physical length of a conductor. For a given amount of r-f current, then the longer a MW vertical radiator is (up to 5/8 wavelengths), the greater the peak radiation it produces. Structures of electrically similar physical dimensions produce nearly the same radiation patterns and gain, other things equal.

IMO radiation from a Part 15 Isotron wouldn't be much different than from a normal, base loaded, short radiator. Both of them benefit by radiation from a long "ground lead" connecting the tx chassis to a buried r-f ground, because that extends the radiating length of the antenna beyond that of the 3-meter section, itself.

//

IMO radiation from a Part 15 Isotron wouldn't be much different than from a normal, base loaded, short radiator.

Ok, so if I understand you correctly, you're saying basically it still looks a lot like a base loaded vertical (albeit with a sort of unusual capacitance "hat") because that's pretty much what it is. And as such the company's claim that:

The ISOTRONS exceed or equal (depending upon the model) the area of a conventional one-half wavelength dipole (#12 wire)...

...Tests have measured the ISOTRONS to transmit as well as a one-half wavelength dipole.

...is probably carefully phrased ad hype. So assuming both are mounted on or very near the ground, it wouldn't do much differently than the base loaded verticals usually discussed here?

Ok! That's what I was wondering when I looked at the design.

Thanks, Rich.

Daniel

Well, confusing to me, anyway. But confusing me isn't really all that hard. LOL

Their insistence in their technical literature that it does not actually rely on the groundwire is probably the biggest confusion I found. Bits like:

Please note that the shield of the coax is not considered to be the same ground as the grounded components of the antenna, such as the mast or bottom plate

... on page 14 of the 80 meter antenna manual. Particularly with the bit about cutting the grounding wire to splice in a capacitor, and using a *NON* metallic antenna support that the metal mast is attached to. I assume that 1000 pf at 160M would effectively pass the rf to ground even though it might block the DC path? But thinking about it, almost any practical operating situation would *still* have an actual connection to ground via the audio lines or the power supply lines. So it may still be radiating somewhat from a ground line, just not where the average person would think of the ground as being.

Their manual is a darned interesting little article anyway, though one might wish they had a manual up for the antenna they make that they claim is part15 compliant. I wonder if there is some difference in the wiring, or if they're just assuming it to be compliant because it's "less than 10 ft tall".

Having started this thread I needs say when talking to the manufacturer while ordering my Isotron and he told me that the ground on the outside mounted Isotron was for discharging static electricity. I believe somewhere on their site they state that an indoor or apartment patio mount doesn't require a ground. I plan to use the antenna with a PCS electronics AM Max II transmitter although I'd like to try it with my SSTRAN too. It's on the PCS site Forum that the home made Isotron is discussed along with Isotron entries on several of their Forum threads from which one can piece together the necessary information for a home brew. As to part 15 compliance of the Model 200B, although the height is less than 3 meters, when the additional length of the capacitance caps are added the 3 meter length is exceeded. I do believe the FCC counts the capacitance cap length. JimB

Rich and others,

I agree with your "physical" science assessment of how a RF ground works. The Isotron is, by design, a tuned L-C tank circuit, resonating within itself. The characteristic impedance of the device over ground produces the propagated radio signal. Other hams have tested this antenna (transmit only) on wooden supports with ferrite line isolators and they work nearly the same as mounted on a metal pole or mast. I know that theoretically it shouldn't, but in practice it does.

Also, just a note: I have engineered and constructed several licensed AM broadcast "Unipole" or folded monopole antennas that seem to work just fine over a non-existent or greatly diminished ground system. Theoretically, it shouldn't, but in practice the measured field strength is significantly greater than a conventional 1/4 wave tower with NO change in the ground system itself. No real explanation why.

The FCC has gone around and around the proverbial scientific pole with broadcasters for decades regarding how to define the different "kinds" of grounds. Your explanation of the workings of the ground path is correct. However, I have no scientific reasoning to explain the operation of some operational radio antennas and associated ground systems, in reality or practice.

To confuse the issue even farther, the FCC, with the assistance of some creative engineers and expensive FCC attorneys, have bent the regulatory interpretation that there is a difference in RF ground, tuned-ground, service ground, safety ground, EMP ground and lightning ground systems. They are all grounds, but according to "accepted" engineering practice, (FCC terminology) they are all different even though they may be intergrated into the same system. Sometimes, FCC rulings get muddled in legal, political and government process and physical science loses out. That is where the term, in broadcast enginering compliance, was authored, "wiggle room".

Rev. Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.

Rhema Radio - The Word In Worship
AM 1660 - FM 93.5
http://www.rhemaradio.org

Do you mean to use a Rangemaster AM1000 with an Isotron? You bethca. Just insert a 3/8-24 X 1/2 stainless bolt, with lock washer, in where the whip normally connects and attach a "short" wire between the transmitter and the antenna feed point. Connect the transmitter ground as directed by the xmtr manufacturer (ground side of the antenna) and you should be in business. Remember, you have only 3 meters to play with for length. Also, you will need to carefully re-tune the transmitter to the new antenna. Be careful of "false" peaks in the tuning indication.

Rev. Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.

Rhema Radio - The Word In Worship
AM 1660 - FM 93.5
http://www.rhemaradio.org