Mentions have been posted/linked here and elsewhere about the possible use of horizontal radial wires attached to the top of a 3 meter vertical radiator -- commonly described as a top hat.
Below are the results of a NEC4.2 study showing their effects, for the conditions given below:
- Frequency = 1650 kHz
- 3-meter vertical monopole base-driven against an 8-ft vertical ground rod directly below the monopole
- Base of monopole within 6" of the earth
- Top Hat = 8 horizontal conductors each 1 meter long, attached to the top of the monopole and deployed at 45° azimuth intervals
- Earth conductivty = 5 mS/m, d.c. 13 (average soil in the continental US)
The feedpoint impedance at the base of this system is about 74 -j 2300 Ω. A base loading coil of about 220 µH would be necessary to resonate the system at 1650 kHz.
With the top hat wires removed from this antenna system, the feedpoint impedance is about 72 -j 3700 Ω, and a coil inductance of about 360 µH is required to resonate it.
Note that the smaller reactance of the system with the top hat requires less inductance to resonate it, rather than more inductance (as some have stated).
Unknown in all of this is the FCC's view on whether or not the top hat wires or even the ground rod need to be included in the 3-meter limit defined in §15.219(b).
The tophat question has been around since the early days along with advocates and debunkers.
At KDX Worldround Radio we have maintained curiosity about them but have never tried it because what we experience with a plain vertical antenna suits our purposes.
The best aproach would be experimentation by those who reach for every inch of extended range by whatever (legal) means available.
Keep detailed notes and report in these forums until finally we know about top hats.
If the FCC inspects it we especially want to know the ourcome.
So Rich explained in his post what a top hat is so now I get it.....somehow I think this would be detrimental as AM transmitters are designed to be tuned to resonance with a vertial 9 to 10 ft antenna and the manufacturers point out that anything that changes that will result in reduced efficiency.
Mark
Thinking about antenna related subjects we had that almost religious experience by comparing and discovering through association opening like a bright light into a whole new world of discovery!
As of this moment I am bestowed the world's leading authority on the topic of antenna top hats but as yet have not shared my realization with another person anywhere on earth.
What I truly believe that I now know is information the FCC does not want you to know! But I will not seek hush money to keep it quiet!
Nor will I sell the vital knowledge to the failing and faltering competition who have lately resorted to stealing posts from our member, plagierizing Artisan Radio's posts on SSD (Solid State Drives and computer speed) while claiming full possession of the knowledge imparted, it being almost predictable that my top hat secret will appear on that site minutes after initial publication.
In the altruistic spirit of the ALPB (The Association for Low Power Broadcasters) the long lost secret of antenna top hats will appear here and at the ALPB Forums simultaneously but not quite yet.
Keep close watch over the next two days... it could be at 2 o'clock in the middle of the night but you are about to learn how top hats may be the holy grail of low power hobby radio!
We at The ALPB do not snitch.
I've got one, but since I bought the Procaster I didn't think I could improve upon anything. Perhaps next Spring I'll throw it together and put it on the AMT-5000 and see what happens.
In my Post # 4 (above) it was told that psychic associational thinking had opened new vistas of awareness about the secret of Making Top Hats Work.
Before launching into my own findings and conclusions, let's send you on a journey of discovery.
Visit this link, study the novel AM antenna presented, think about it and top hats at the same time. Ask your family to hold it down so you can concentrate.
Then watch back here for my prophesied return.
This Major Forum Presentation is Being Released Simultaneously On the World's Two Major Low Power Radio Forums