I looked at that YouTube link you
just posted. Very impressive work.
I wish I could build antennas like that.
Especially portable ones.
Best Wishes,
Bruce, 90.9, 88.3
You Isotron guys should read these two links:
http://www.antennex.com/preview/archive5/Oct602/introisotron.htm
http://www.google.com/url?sa=t&rct=j&q=&esrc ="s&frm=1&source=web&cd=2&ved=0CCUQFjAB&url=http%3A%2F%2Fwww.antennex.com%2Fpreview%2Farchive5%2FNov402%2Fisotron2.pdf&ei=xylUUNmzGY-v0AGDz4CwDQ&usg=AFQjCNG9Jpu0VK7s8lhnFz09e80Rr7PZCw&sig2=cvyG7jiWZnDtDxhODdE6aQ"
Those are great PDF's on the Isotron. And exactly what would result with that particular Isotron and configurations and frequency of operation, which that Isotron isn't for MW.
But for Part 15 MW, where 3 meters is the zone, and when access to an Earth ground is impossible, a 3 meter size Isotron built for MW does work far better than a simple wire.
The hight to impedance ratio is about the same however. Not much of a problem in a typical setting, but in a hi-rise apartment complex or building and your on the 15th floor, impedance of the MW Isotron rises just as it does for it's HF counterparts, so take that into account for those in such hi-living situations. That is probably the biggest error made when those trying an Isotron neglect to take into account during the build of the antenna the hight from actual Earth ground plays a role in how that thing will match up to your TX. haha! :p
RFB
Yes, according to RFB, but probably not indoors or near obstructions.
Many thanks to PhilB for linking the exceptionally thorough Isotron study undertaken and shared by Dave Cuthbert, WX7G.
The Isotron probably wouldn't be "wife friendly" inside the house, it isn't exactly artful in appearance.
The advantage of what has just been presented for readers here at part15 is that we can go on with a better idea of what the Isotron has to offer.
For outdoor, it remains to hold a competition between the Ultenna, PhilB's all time vertical with ground radials, and the Isotron.
One out distance the other?
Are hard to beat! Those old "Experimenters" were wise 'ol birds to figure all of this out. Not too many magical changes have been made to their basic discoveries..
GROUND MOUNTED:
Advantage to Isotron due to its capacitive top hat. No advantage if you add a top hat to a classic base loaded vertical.
ELEVATED MOUNT:
Toss up. The advantage of the top hat is swamped out by the substantially higher radiation from the coax or ground wire. There is minimal advantage from the Isotron "bottom hat". It will act as a minimal elevated counterpoise. It's too small to act as an effective elevated counterpoise.
TUNING:
The Isotron has tuning adjustments that vary the antenna capacitance. I suspect the tuning range is relatively small. I don't think the coil is tapped. You can have a much wider tuning range with taps on you classic base loaded antenna coil.
GROUNDING:
You need a ground wire for both antennas whether mounted at ground level or elevated. It' for lightning discharge safety!
COST:
Although the Isotron is quite expensive, individuals should weigh that cost against the parts cost and time and effort involved to build a classic base loaded antenna.
Neither antenna can be used with a transmitter that has an internal loading coil, unless the internal coil can be bypassed.
The Isotron is designed for coax feed, but you don't need to use coax. You can mount the transmitter immediately below the isotron and feed it with a short wire, just like a classic base loaded antenna.
The Isotron for Part 15 MW, cannot have a coax. Thus it is fed directly with a transmitter placed below it, as would be a monopole over a radial system.
The cost to make one...FAR less than a monopole over a radial system.
Tuning can be done two ways. Tapping the coil and/or a variable capacitance. Tuning by increasing the upper plate distance cannot be done in Part 15 MW because you may end up exceeding 3 meters length.
Elevating onto a pole using a ground wire or power wire or audio wire isn't a good idea either. The MW Isotron isn't designed or intended to be operated in that fashion.
Though it can be operated beyond Part 15 limits and perform very well, it's no different from going beyond the Part 15 limits with a monopole, such as elevated using a ground wire down to the radials.
If comparisons are going to be made, then make them with comparing it to the right counterpart, the Part 15 ground mounted monopole.
The Isotron does work good indoors. It's not easy however setting it up because of it's height versus your room's roof height. Sitting that close to the floor and roof, some change will occur in it's resonance and tuning.
A quick "poor man's" Isotron:
1- 9 foot long non-conductive/inductive tube 3 inches diameter.
#18 AWG insulated solid copper magnet wire.
#22 AWG insulated solid copper magnet wire.
2 12 or 15 inch pizza pie pans.
Begin by wrapping 220 turns of the #18 wire at the bottom of the tube, close wound. Then take the #22 wire and wrap from the top of the bottom coil with about 4 inches gap between windings, all the way to the top of the tube. Connect the upper winding's lower lead to the lower coil's upper lead.
Install pizza pie plates at the top and bottom, making an electrical connection to the top coil and lower coil with the pie pans.
Transmitter ground connects to lower pie pan. Transmitter "hot" connects to a tap on lower coil from about half way to about 3/4 from the top, depending on frequency (rough tune). 350pf variable across tap and ground for fine tuning.
There you go, a very effective and VERY inexpensive Isotron.
RFB
per isotron. the 200b is a 160c with a larger coil for the lower frequencies.
The Isotron, to me, looks like a place where a bird could build a fair nest.
As long as that came up, do birds ever make nests on antenna elements, like the "bays" of an FM antenna?
As long as the subject of birds is still up for discussion, would there be a capacitance problem if small birds came and went from a wooden house at the top of a 3-meter pole?
"would there be a capacitance problem if small birds came and went from a wooden house at the top of a 3-meter pole?"
Yes, it will have an effect, not much but it will.
I once had a 3 meter antenna system with a 2 foot diameter top hat. For some reason the birds loved to perch on that top hat more than the trees, and every time one parked on it, it would shift the tuning.
So I improvised and strung a length of fishing line with salvaged plastic lids attached along the fishing line. The plastic lids had mean bird faces drawn on them. They would swing and wave in the wind, keeping the birds at bay!
Fortunately no birds ever "clothesline" themselves!
RFB
Now we know that mean faces improve antennas.
I tried the same idea with the tree squirrels. It did not work. The tree squirrels began collecting pieces of the plastic lids and hauling them off to their huts elsewhere. In the end all that was left were ragged pieces of plastic butter bowl lids!
Maybe I should have drawn the face of a hungry fox on the lids!
The tree squirrels continue to gather and sit and hold membership meetings on top of my outdoor 3 meter antenna box.
RFB
Girl friend # 76 took me to visit an elderly lady whose hobby was watching the birdfeeder outside her kitchen window. On the wall near the kitchen sink was a door-bell button which she pressed whenever a squirrel got on the feeder. Pressing the button sent a tremendous electric shock on a wire that was strung around the platform of the feeder. Squirrels flew.
...Pressing the button sent a tremendous electric shock on a wire that was strung around the platform of the (bird) feeder. Squirrels flew.
Interesting. And did the birds then climb the trees?
What usually seemed to happen is that when squirrels showed up the birds flew away, so the woman had a clear shot.
But it is fascinating to imagine the one bold bird who stayed on for a face-down with the squirrel, and got jettisoned with the jolt.
Life has its share of sad stories, often intermingled with funny ones.
If it weren't for part 15, none of this would matter.