Isotron with SSTRAN AMT5000

Hi Ken!

The person with reported Isotron experience is RFB, and he checks here a lot, so he'll probably give the answer you're looking for.

In the meantime I get to give an opinion, which may not be exactly correct.

I think the Isotron expects a standard 50-ohm input, but since they make special models for Part 15, there may be an exception. But here's why that's important.

The AMT5000 was very intelligently designed around the fact that Part 15 only allows a 3-meter antenna, whereas licensed AM more typically has 1/4-wave antennas.

The 50-ohm standard is designed around tall 1/4-wavelength antennas, but does not agree well with short antennas.

The AMT5000 provides an exact match to a short (3-meter) antenna, plus a good grounding system.

Even with all that, there could be a way to make the Isotron match.

Check to find out the impedance of the Part 15 Version of the Isotron. That is probably the key to everything.

Love Tiny Radio!!!

Well for starters, the Isotron does not require a ground plane, or in your case, ocean ground.

The name given to the antenna "Isotron" is more than just a name for it. The first three letters are the clue. "ISO", short for "isolation/isolated".

This means the antenna does not need a ground plane, which works perfectly for situations like hi-rise apartments or rooftops with limited space to lay down radials.

With the AMT5K's efficiency, putting most of the RF to the output instead of dissipating in active element heat, the Isotron will perform exceptionally well.

When I used mine, I was driving it with an AMT3K, on a 3rd floor apartment dwelling. It was placed at one end of the room and the transmitter was mounted directly beneath the antenna. The whole thing was mounted on an old music stand tripod with the top of the Isotron about 4 inches from the ceiling. Coverage was rock solid throughout the complex and in each building.

Outdoors it will perform even better, and with the AMT5K should work incredibly well..if the AMT5K output can match up to it's 50 ohm impedance. Somewhere in the thread abyss is a discussion about the matching up of the AMT5K to a 50 ohm load or Isotron. PhilB should be able to add more additional info on that.

RFB

Wow what a cool looking antenna .
No grounds ?
I have got to give one of these a try.

RFB, is this the one you were using?
http://isotronantennas.com/index.php?main_page=product_info&cPath=1_4&products_id=15

Yes End80, and a home brew version slightly different.

RFB

Hi Ken,

The Isotron will work with the AMT5000 with one caution. Coax can't be used between the TX and the antenna. Instead, a relatively short wire (no more than maybe 2 ft. tops) should be connected from the TX antenna terminal to the center pin of the coax connector on the antenna. The TX ground terminal should be connected with a separate wire to the bottom end plate on the antenna. The AMT5000 has a jumper option to bypass internal tuning. This jumper plug must be installed.

In general the MW version of the Isotron is really a base-loaded vertical. The loading coil can be seen near the bottom. Also, there is a capacitance top hat (top end plate) and an adjustable tuning rod at the top for fine tuning. The bottom end plate could possibly be considered a rudimentary elevated ground plane, except it is too small to have that effect. There are no taps on the coil, so it will tune only within a fairly narrow range of the frequency you specify when ordering. Since the tuning rod is near the top, you should consider that access to it will be needed when installed in its final location on the roof. You can't tune it on the ground first because the tuning conditions will be different on the roof.

Here are two links from the Isotron site you should study to gain understanding.

PICTURES
http://isotronantennas.com/index.php?main_page=page&id=12

INSTRUCTION MANUAL 160C MODIFIED ALSO AM BROADCAST BAND MODELS
http://isotronantennas.com/download/inst160cmodified.pdf

Particularly, you should read the sections in the manual that discuss grounding. They recommend grounding the bottom of the mast. If that is not done, then they say the ground will be through the coax shield to the transmitter ground. In, your case, you should connect a heavy-gauge ground wire from the bottom of the mast on the roof, down the outside of the building, to earth ground. This will improve performance and provide that all important safety ground.

you should connect a heavy-gauge ground wire from the bottom of the mast on the roof, down the outside of the building, to earth ground. This will improve performance and provide that all important safety ground.

Ummmm... yeah.

My take on what PhilB said about the ground wire was plain technical advice based on how to get an Isotron to work properly with a part 15 AM transmitter.

If there is a hidden meaning, it is not to suggest that we break the rules by using an improper ground wire, but that the Isotron makers themselves may not have revealed everything regarding the effective implementation of their antenna design.

I am out on a plank here, and may be on the wrong path, but I am certain that PhilB is not suggesting we violate the 3-meter rule.

At this time I invite rebutts.

Carl,
Thanks for pointing that out.

... I am certain that PhilB is not suggesting we violate the 3-meter rule.

Oops, I guess it looks like I violated my own previously stated position of neutrality on the 3 meter rule. I did only wish to point out that the Isotron manual says there must be a ground, either by grounding the bottom of the mast pipe, or through the coax, when used. The lightning safety issue is simple and mandates a ground wire to earth. I should have added words around the phrase "improve performance" to point out that it raises the 3 M rule issue and should be considered by the individual user. I really didn't intend it as a recommendation to violate the 3 meter rule, but it obviously came out the wrong way. Its too late to edit that post.

PhilB's point of a proper ground for lightning protection is valid, however as long as the ground lead issue debacle is unresolved and remains undefined with clarity from the OET/FCC, it is and will remain just that...a debacle.

Not to re-open old wounds, but this is why the choke along that ground line will help reduce radiation from that long ground line. Though not entirely, it is better than no choke and a ground line radiating more than the intended radiating element, be it a monopole or Isotron.

However if the Isotron is set up 1 meter off the ground, there is no worry as every certified Part 15 device is tested 1 meter over an artificial ground system in the testing chambers with the DUT connected to that artificial ground system either through the table which is metal that the DUT is sitting on, or through a wire connected to that artificial ground below it.

Regardless, using an Isotron or a loaded 3 meter monopole on a roof installation, your going to face the debacle endless loop argument over the exceeding 3 meter limit thing and ground line radiating debate.

RFB

"The 50-ohm standard is designed around tall 1/4-wavelength antennas, but does not agree well with short antennas."

True..for far field radiators. However look down there in the basement..ie the CC system, which has a 50 ohm standard input impedance coupling to a much different impedance on the output of the coupler while maintaining the 50 ohm input impedance standard.

Now with short radiators to produce far field, the short radiator CAN be matched up with a 50 ohm impedance standard with the right matching circuitry. The TCU-8/30 and CP-15 couplers would do that very nicely btw.

The Isotron manual reference to needing a ground is not a definition of needing a ground for antenna performance or functionality whatsoever. It is for lightning protection and nothing more. The Isotron in of itself to operate (resonate) and emit a signal requires no additional ground attached to the lower plate. In most cases the reason for using an Isotron is because of limited access to Earth dirt for a grounding system. Though they can be used outdoors and elevated, they still do not need that ground line to Earth dirt below to operate or shoot a signal. That ground line going below only serves for a lightning or static charge dump..ie pathway to Earth dirt.

The 15.219 Isotron does it's best sitting on it's own in situations where access to that Earth dirt is hindered, such as apartments or hi-rise buildings, and excellent for indoor uses, ground level or elevated. But when outdoors in the open, on top of roofs or up on a mast, to meet NEC safety requirements you need that ground line no doubt. But the Isotron does not require that ground line to function as an antenna or require it to bring it to resonance.

What happens at that point is the long ground lead issue and the radiating ground lead issue..to which that round and round merry go round circus needs no further spinning or discussion. And I say it again, no matter if it's an elevated Isotron or elevated 3 meter monopole, the ground lead length/radiating/lighting protection argument applies to both.

The only difference, elevated or not, is that the Isotron does not need any help with a ground to function, whereas the 3 meter monopole does.

RFB

i am discovering the amt5000 wants to see that specific antenna capacitance and the taps have very little affect in tuning out anything outside of that small window of capacitance on the radiator. at least at 1670 anyway.

i have determined the ground does not have much of an effect on tuning as the antenna capacitance does.

kc8gpd I agree with your statement...

"i have determined the ground does not have much of an effect on tuning as the antenna capacitance does."

And I would add this important additional experience on my part...

There is an area uphill from the transmitter that had no signal at all before I added ground radials, the signal was only good in the downhill direction.

After I added radials in the ground the signal up the hill is now as solid as it is near the transmitter.

works nice in an isotron type configuration. but the one word of caution is watch that top hat. the amt5k wants to absolutely see phils suggested capacitance range. you will not get that peak without it.