"ght, and you could offer Part15 compliant haircuts on the side"
Huh??? Oh, I get it. No, not barber poles, they corkscrew around. I mean something like this little tower:
I think five bands would look about right on a 10' pole. Spec colors are white and International Orange.
Also, concerning loading coils, here's one y'all might like:
http://www.lbagroup.com/technology/super.php
... but you might want to build a nice little white and International Orange checkerboard hut for it 😉
I've been working on a scale tower design, i.e., a 10' scale version of a real commonplace free-standing commercial AM radio tower.
My concern is that I want a little red flashing light on top, but I'm afraid it will either suck up precious signal amps, or interfere, or maybe just explode ...
Ken Norris, You've asked several questions I still have about the cage monopole, particularly the question of eddies and phasing. I didn't myself consider eddies until you mentioned it, but the phasing is an issue because of the time difference between nearby points in space, that is, the distance in space and time between the elements. Look ast it this way: when you are standing nearby, some of the elements will be close and some farther away. That means the signal from the nearest elements will reach you first, then the farther element's signals, perhaps causing a small bit of phase cancelation.
I can report that for an indoor FM setup a 4-element cage works better than 1-wire because it actually overcomes multipathing caused by people walking in the field.
I am just about to try cage monopole on AM, and I will write about that.
Using pipes to build a cage... another great question.
Grounding for the cage would be exactly the same as for a 1-wire or 1-pipe antenna.
Using flimsy wires, etc., simply to make it cheap and easy to try.
Tuning is no different - it will need a loading coil, albeit a smaller coil, which is part of the hope, reduced coil resistance means a tiny bit more juice to the listeners. In theory, the tuning would be a bit more forgiving as the bandwidth is greater
I doubt it could be considered an array, in part because it's shorted to all points.
It's grounded like any other antenna, in this case ten turns from the bottom of the loading coil.
As far as phasing, etc., we're talking about wavelengths hundreds of feet in length so I'm guessing the cage looks like a single radiator to the signal.
I would anticipate more even coverage, easier tuning and a small but noticeable extra bit of range.
There was an interesting antenna out there for a while made by the GAP antenna company.
Here is a LINK to info about the "Super C" antenna which works on the idea of very large surface area (Caged Monopole) to reduce the loading coil needed.
They seem to have discontinued it but I did read a favorable review.
That is a cool idea Ken.
My concern is that I want a little red flashing light on top, but I'm afraid it will either suck up precious signal amps, or interfere, or maybe just explode ...
How about maybe gluing a ball bearing or a little round mirror to it, and then modify an inexpensive pen laser to blink and beam onto that mirror.. http://www.dinodirect.com/red-lasers/
edit: Actually a clear glass bead would probably be more effective, that way when the red laser hits it; the glowing red sphere could be seen from all directions
Looks like it came from a mink farm.
The problems are that it looks like it's being used with 200 watts, plus it shows 20 meters then next to that 300kHz minimum ... which is nowhere near 20 meters. I'd like to know what it will do at 160 meters (closer to high end of the AM BCB).
If it would do well with 100mw final input even at the low end of the AM BCB, it might be the solution for the apartment dweller with little space.
The magnetic loop antenna I saw awhile back is just 3' square and can penetrate rock walls. A number of folk here said such an antenna would not be efficient, but the proof is in actual use. So, I think I'll go ahead and wake up those old formulas and start running numbers. My engineer friend (60 years in the business) who also thinks it should work will show me how to build a matching network for it.
ITMT, I believe this article, diagrams and photos, has been posted before, but here you go (scroll down 'till you see the square copper tube):
http://www.techlib.com/electronics/amxmit.htm#field%20strength%20meter
I have been monitoring the discussion here regarding the Caged Monopole antenna system. I offer my experience to the discussion.
The original research on the antenna system known as a Folded Unipole or Monopole antenna was developed as a graduate research project at the U.S. Naval Academy. The focus of the research was to discover if the antenna design produced an increase in theoretical signal strength over a standard quarter wave vertical with ground radial system. The Folded Unipole was tested with the same ground radial system as the standard vertical. In a nutshell, here are some of the findings.
The Folded Unipole antenna system produced the same field strength as the standard vertical antenna system. However, depending on the length to diameter ratio, the Folded Unipole exhibited a considerable increase in operational bandwidth. This increase would naturally add to the high frequency audio side band response of a transmitted AM signal. In some cases, AM sounded as good as mono FM.
Because the "folds" of the Unipole antenna are hung on another structure of some sort (tower, mast or non-conductive structure) one would think that the support structure would be part of the antenna system. Not so. In fact, research and practice show that the Unipole system doesn't even see the support structure electrically. The fold wires are connected to the top of the metallic structure or return wire, and insulated from ground at the base and fed signal by a common feed ring. Most AM broadcast towers/support structures using Unipole antennas are grounded at the base, unlike standard broadcast vertical systems that sit on an insulator. The grounded tower allows for the mounting of other RF service antennas directly to the support structure without other isolation from the Unipole system (cell phone, vhf/uhf radios, STL systems, TV translators, etc.). These additional antenna systems don't seem to effect the Unipole at all.
The best part of the Unipole antenna is impedance matching; a simple task. Regardless of the length of the support structure, the Unipole can be any near resonant length or even non-resonant. Impedance matching can be done with a mid-fold shorting ring (or shunt) to the metallic, grounded support structure or a simple Pi-network at the feed point. The shorting ring shunt can be adjusted so that the feed point impedance is less than (but near) 50 Ohms exhibiting inductive reactance. This would mean that a series connected variable capacitor could be used to cancel out the reactance while still maintaining a wide antenna bandpass and increased network efficiency. No coils are necessary.
I have designed and built two of these antenna systems over the years for commercial AM BCB stations. They are still in service 25 years later. My experience has indicated that these Unipole antenna systems, for some reason have the ability to overcome poor ground systems and ground conductivity to produce a marketable commercial radio signal. One station is 5 KW daytime and 150 watts at night, with a very poor ground system and a very listenable signal in a community of 600,000 stretching over 25 miles.
Included here is a link from the firm and engineer that pioneered the use of the Unipole system in broadcasting:
This antenna system design has been successfully used by amateur radio operators working overseas with a kilowatts or less on 160 meters (1.8-2.0 MHz) for decades. Hams call this antenna a shunt feed folded vertical in the antenna manuals. It is the same antenna as a Unipole, just simplified. The final word on this antenna design is that for Part 15, the increase in signal strength of a 3-meter standard vertical antenna system compared to a Folded Unipole would be almost imperceptible. That doesn't mean it wouldn't be fun to build one, just to see how it works. Mullaney's design would be a good starting point.
The antenna plan or the cool 1986 electronics ads
Memories... 🙂
Thank you for the cool link!