Short fat antennas are more efficient? Wider bandwidth yes.
All antennas are built from metal of one kind or another.
WDCX is right, as far as I know, that "fat" metal has better bandwidth, up to a point I'd guess. There is probably such a thing as "too fat" where there would be diminishing returns.
And I share skepticism over the notion of "shorter" being in any way advantageous, although there is talk in the industry of designing "smaller AM antennas" as part of revitalization, but we'll believe it when we see it.
Which brings me to a new question I have had for a long time... do DENSER metals improve efficiency?
What is the MOST DENSE metal available for making an antenna?
Osminum is the MOST DENSE but the conductivity is not a good as Silver. Now to answer your question, density in my opinion is moot as radio frequency currents tend to travel on the surface of the conductor rather than through it.
From what I've been reading, the "smaller AM antennas" being talked about seem to be half or quarter size of current towers, and needing proportionately smaller ground planes, to fit on smaller areas of land and in areas where there are structure height restrictions like airplane flight paths.
Some will be fed higher on the structure like a unipole, I think that's the one being talked about, or be a short tower with a long cross shaped capacitance hat. No matter what, these antennas are going to be less efficient, with signal strength made up for by increasing power.
I haven't seen anyone propose ten foot antennas as in our service, more like the idea is a heaight similar to other structures in the area.
Thats mainly because a 10 foot antenna is so horrifically inefficent in the Medium Wave band. Its great for CB up at 27 mHz though.
3-meter antennas are also just about right for the FM band.
Mighty 1650 said: "a 10 foot antenna is so horrifically inefficent in the Medium Wave band".
I know nothing about the technical end of this, but would an AM antenna be more efficient if LESS than 10'? Is it the wave length that is so bad or just the short length of the physical antenna?
Is it the wave length that is so bad or just the short length of the physical antenna?
It is the electrical length of a 3-meter antenna compared to the wavelengths used for AM broadcasting in the medium-wave band.
Antenna systems using vertical monopoles become more efficient as they get longer (taller) in terms of electrical wavelength. For reasonable system efficiency they need to be at least 1/8 of a wavelength at the operating frequency.
For example, a wavelength at 1700 kHz is about 176 meters, so a 3-meter monopole is about 3/176ths of a wavelength there -- and has poor system radiation efficiency.
Medium-wave antenna systems using monoples of less than 3 meters would have even worse system efficiency.
Two words everyone needs to think about and read the older articles about. Harmonic Antenna. Sometimes less equals more if you want a compact antenna. Think Star Antenna for AM and also think about the 40 meter/15 meter harmonic antennas for Ham Radio. So you take that figure for AM and use the 1st harminic, 2nd harmonic, 3rd and so on till you get it as compact as possible. Plus the thickness is another factor. All can be made to fit the rules without going over. Hey that is what this initiative is all about. We are trying to change some of the restrictions for AM due to the raised noise factor and to make that 100 mW work better. Even if we don't get the 2 Watts for AM, we should get the limit taken off the antenna length now that the status for AM is not the same as it was in 1934.
Thelegacy wrote: "... Think Star Antenna for AM and also think about the 40 meter/15 meter harmonic antennas for Ham Radio. So you take that figure for AM and use the 1st harminic, 2nd harmonic, 3rd and so on till you get it. ..."
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Specifically what is meant by "use the 1st harminic, 2nd harmonic, 3rd and so on till you get it?"
I've never heard that either. I suppose antennas obviously hit key wavelengths on multiple frequencies, but none of which will resonate for the MW band at 10 feet or less.
There are formulas for ½ wave antennas like 468/frequency and the like. So you figure the harmonic that is less than the actual frequency and keep going down till you hit or go under 10 foot for AM. There are many articles in older magazines such as Popular Electronics and Ham Radio Horizons, but you'll have to look back to 1967-1978 or so to get these articles. There has even been antennas designed for commercial broadcasting but at much smaller lengths than a regular sized AM antenna. This antenna project that Station8 and a few beta testers has been researched based on actual homework and understanding many different designs. Nothing said in the FCC rules you have to use only a steel whip or piece of wire for an antenna. So think outside the box and have a happy antenna building project for your part 15 station. Or just sit back and wait till we can get this antenna machined for those who just want plug and play.
Thelegacy wrote: ... So you figure the harmonic that is less than the actual frequency and keep going down till you hit or go under 10 foot for AM. ...
Harmonics of a frequency are integer multiples of that frequency, which never are less than the original frequency, itself.
There is little reason to use an antenna cut for a harmonic of the operating frequency. It might radiate that harmonic more efficiently, but radiate the operating frequency LESS efficently.
... There has even been antennas designed for commercial broadcasting but at much smaller lengths than a regular sized AM antenna. ...
They are shorter, but heavily top-loaded. Their radiating length is much longer than the 3 meters allowed for compliant Part 15 AM.
How about negative frequencies Rich? 🙂