But then, aren't we saying that the added horizontal lengths up on top of the Star-H are doing much the same thing good coil loading would do?
Yet, at the same time, the "Litz" method of driving 4 parallel vertical legs so as to bring the impedance down has its appeal. So maybe driving 4 coils and 4 verticals in parallel would do the same as a Star-H minus the horizontals on top.
Laboratory time.
But then, aren't we saying that the added horizontal lengths up on top of the Star-H are doing much the same thing good coil loading would do?
Yet, at the same time, the "Litz" method of driving 4 parallel vertical legs so as to bring the impedance down has its appeal. So maybe driving 4 coils and 4 verticals in parallel would do the same as a Star-H minus the horizontals on top.
Laboratory time.
As has been stated here, a properly designed "top hat" does not radiate but does aid an antenna in radiating by changing the distribution of current on the antenna. It also adds capacitance to the antenna which, although not physically longer. becomes electrically longer.
In my case, the antenna which I built and featured on my website some time ago utilizes a capacitance hat to lower the resonant frequency of the antenna even though it was not at the top. It does so by increasing the total capacitance of the antenna which offsets the fact that the antenna was a tad shorter (read smaller inductance) than required.
I've read pros and cons regarding the FCC's take on a 3 meter antenna with a top hat. But, in either case there is nothing wrong with using a top hat on a Part 15 transmitter in so much as it is not going to harm the transmitter. Yes it will alter the resonant frequency but that is designed into the antenna to work with the transmitter to which it is attached. By the same token, a properly designed ground counterpoise does not radiate but definitely aids an antenna by reducing ground losses. There again the FCC probably frowns upon artifical grounds such as that.
Carls idea of parallel wires is not unlike that of some antennas I've seen. Fed from a common point, three radiators each slightly different in lenght are each resonant at slightly different frequencies; ie 1505, 1500, 1495 kHz. Like the "Fan Dipole" but covering a very small range of frequencies the bandwidth is larger, more suitable for AM than a single radiator. Many discussions here have pointed out problems with electrically short antennas having very narrow bandwidths. I wonder how the FCC would view that type of antenna? Would it be the same as a single conductor, Litz wire or using a top hat?
This started out as trying to answer one question but seems to have raised many more...
As has been stated here, a properly designed "top hat" does not radiate but does aid an antenna in radiating by changing the distribution of current on the antenna. It also adds capacitance to the antenna which, although not physically longer. becomes electrically longer.
In my case, the antenna which I built and featured on my website some time ago utilizes a capacitance hat to lower the resonant frequency of the antenna even though it was not at the top. It does so by increasing the total capacitance of the antenna which offsets the fact that the antenna was a tad shorter (read smaller inductance) than required.
I've read pros and cons regarding the FCC's take on a 3 meter antenna with a top hat. But, in either case there is nothing wrong with using a top hat on a Part 15 transmitter in so much as it is not going to harm the transmitter. Yes it will alter the resonant frequency but that is designed into the antenna to work with the transmitter to which it is attached. By the same token, a properly designed ground counterpoise does not radiate but definitely aids an antenna by reducing ground losses. There again the FCC probably frowns upon artifical grounds such as that.
Carls idea of parallel wires is not unlike that of some antennas I've seen. Fed from a common point, three radiators each slightly different in lenght are each resonant at slightly different frequencies; ie 1505, 1500, 1495 kHz. Like the "Fan Dipole" but covering a very small range of frequencies the bandwidth is larger, more suitable for AM than a single radiator. Many discussions here have pointed out problems with electrically short antennas having very narrow bandwidths. I wonder how the FCC would view that type of antenna? Would it be the same as a single conductor, Litz wire or using a top hat?
This started out as trying to answer one question but seems to have raised many more...
MRAM made the observation that this thread asked one question but branched into many more, and that's true, but I argue that everything that's been said is related to the original question. I see the top L-bends into horizontal branches as having the same net effect as a top hat.
Another observation, probably obvious, is that it becomes often necessary to discuss the larger scale of licensed technology and then try to reduce the size to fit Part 15 limitations.
One question buried in this ongoing dialogue which has not been directly confronted is my posing the "cage monopole" (a term only now being introduced to this thread), consisting of four parallel 3-meter antennas all fed from a single transmitter, as being equivalent to a single 3-meter wire, except lower in impedance. I likened it to a Litz wire for its multiple-wires-in-one.
The paper on the Star-H says, "It is well known that creating a cage monopole of vertical wires to increase the diameter of the radiator can increase the bandwidth of a short vertical antenna." That comment gives an especially appealing reason to consider the cage monopole as a realistic Part 15 design.
MRAM made the observation that this thread asked one question but branched into many more, and that's true, but I argue that everything that's been said is related to the original question. I see the top L-bends into horizontal branches as having the same net effect as a top hat.
Another observation, probably obvious, is that it becomes often necessary to discuss the larger scale of licensed technology and then try to reduce the size to fit Part 15 limitations.
One question buried in this ongoing dialogue which has not been directly confronted is my posing the "cage monopole" (a term only now being introduced to this thread), consisting of four parallel 3-meter antennas all fed from a single transmitter, as being equivalent to a single 3-meter wire, except lower in impedance. I likened it to a Litz wire for its multiple-wires-in-one.
The paper on the Star-H says, "It is well known that creating a cage monopole of vertical wires to increase the diameter of the radiator can increase the bandwidth of a short vertical antenna." That comment gives an especially appealing reason to consider the cage monopole as a realistic Part 15 design.
The original government studies involving parallel vertical radiators (Folded Monopole), or a cage monopole, was conducted by the U.S. Navy years ago before it was developed for commercial antenna use or patented for commercial use. I used to have a copy of the original study. It was quite revealing. The outcome was that, even though the bandwidth was increased, the efficiency of a single radiator of the same length (i.e. a tower) was essentially the same; all things being equal (radiator, feed system, ground system). The study involved development of the Folded Unipole antenna design. More information on the Unipole antenna system is available here:
http://en.wikipedia.org/wiki/Folded_unipole_antenna
The Star-H, or Kintronics, antenna system is essentially an out growth of the same body of antenna design and theory. The KinStar antenna is used primarily where a tall tower cannot be erected due to height restrictions, usually because of proximity to an airport or heliport (KCST AM). Several Companies construct and sell the Folded Unipole as stock in trade. The Folded Monopole has been used for VHF and UHF communications for many decades. Even a version of the antenna has been published in the "ARRL Antenna Book" for decades. Here is more information for your consumption:
http://ezinearticles.com/?Grounded-Folded-Monopole-Antenna---Tunipole&id=4435064
Because of the physical mass and weight of this antenna design, using it for the purpose of improving the antenna system for the Rangemaster would necessarily cause stress the transmitter casing and possible compromise of the transmitter with moisture. Any perceived improvement to the Part 15 signal would be minimal at best.
I have personally designed and installed 2 Folded Unipole antenna systems with great success. Both of the systems were installed to overcome ground system losses. The ground systems in both stations were either seriously compromised or constructed in soil with next to no conductivity (near pure silica). Efficiency of the system did improve somewhat. Bandwidth was improved as well. The vertical was very near 90 degrees in length in both cases. And, both are still in operation today, after 20+ years of service (KORE AM & KLOG AM).
The original government studies involving parallel vertical radiators (Folded Monopole), or a cage monopole, was conducted by the U.S. Navy years ago before it was developed for commercial antenna use or patented for commercial use. I used to have a copy of the original study. It was quite revealing. The outcome was that, even though the bandwidth was increased, the efficiency of a single radiator of the same length (i.e. a tower) was essentially the same; all things being equal (radiator, feed system, ground system). The study involved development of the Folded Unipole antenna design. More information on the Unipole antenna system is available here:
http://en.wikipedia.org/wiki/Folded_unipole_antenna
The Star-H, or Kintronics, antenna system is essentially an out growth of the same body of antenna design and theory. The KinStar antenna is used primarily where a tall tower cannot be erected due to height restrictions, usually because of proximity to an airport or heliport (KCST AM). Several Companies construct and sell the Folded Unipole as stock in trade. The Folded Monopole has been used for VHF and UHF communications for many decades. Even a version of the antenna has been published in the "ARRL Antenna Book" for decades. Here is more information for your consumption:
http://ezinearticles.com/?Grounded-Folded-Monopole-Antenna---Tunipole&id=4435064
Because of the physical mass and weight of this antenna design, using it for the purpose of improving the antenna system for the Rangemaster would necessarily cause stress the transmitter casing and possible compromise of the transmitter with moisture. Any perceived improvement to the Part 15 signal would be minimal at best.
I have personally designed and installed 2 Folded Unipole antenna systems with great success. Both of the systems were installed to overcome ground system losses. The ground systems in both stations were either seriously compromised or constructed in soil with next to no conductivity (near pure silica). Efficiency of the system did improve somewhat. Bandwidth was improved as well. The vertical was very near 90 degrees in length in both cases. And, both are still in operation today, after 20+ years of service (KORE AM & KLOG AM).
The Star-H or KinStar antenna developed and marketed by Kintronics is being used by a live AM BCB station here in Oregon; KCST AM. Here is the link to a "Radio World" story on the station and the antenna:
http://radioworld.com/article/77198
KCST AM-Florence, Oregon, is licensed for 900 watts and has one of the better signals on the coast; at least nearly equal to the 50 KW box a few miles to the south in Reedsport. Radio stations right on the Pacific Ocean coastline don't produce a great ground wave signal over land customarily (ground conductivity is poor and salt air destroys ground systems).
The article is pretty self explanatory. My company has been looking at installing one of these systems near an existing airport for sometime. In commercial service the only drawback is the complete required antenna proof when its all installed to prove to the FCC it will spec out to their standards.
Just a guess, but this antenna would not present measurable or perceptible signal increases for Part 15 stations with only 3 meters of allowable conductor length (FCC considers only the total length, not height or width).
The Star-H or KinStar antenna developed and marketed by Kintronics is being used by a live AM BCB station here in Oregon; KCST AM. Here is the link to a "Radio World" story on the station and the antenna:
http://radioworld.com/article/77198
KCST AM-Florence, Oregon, is licensed for 900 watts and has one of the better signals on the coast; at least nearly equal to the 50 KW box a few miles to the south in Reedsport. Radio stations right on the Pacific Ocean coastline don't produce a great ground wave signal over land customarily (ground conductivity is poor and salt air destroys ground systems).
The article is pretty self explanatory. My company has been looking at installing one of these systems near an existing airport for sometime. In commercial service the only drawback is the complete required antenna proof when its all installed to prove to the FCC it will spec out to their standards.
Just a guess, but this antenna would not present measurable or perceptible signal increases for Part 15 stations with only 3 meters of allowable conductor length (FCC considers only the total length, not height or width).
You guys have a lot of it and I
appreciate it.
Best Wishes
Bruce, MICRO1690/1700
You guys have a lot of it and I
appreciate it.
Best Wishes
Bruce, MICRO1690/1700
A capacitive hat improves antenna efficiency by increasing the radiation resistance of the antenna and increasing antenna capacitance. Increasing the diameter of an antenna does not increase radiation resistance much, but it does increase antenna capacitance.
I recently received a message addressed to me personally that claims that radiation resistance alone determines antenna efficiency, and antenna capacitance merely increases the antenna bandwidth. I've heard this opinion expressed before.
Increasing the diameter of an electrically short antenna improves efficiency by reducing the loading coil inductance needed to tune the antenna to resonance. A smaller inductance coil can be made with less loss resistance. Loading coil loss is a major component of Part 15 AM antenna inefficency, and the higher the antenna capacitance, the better.
The Rangemaster uses a CB whip, which has a small diameter. Using a larger diameter pipe would allow the transmitter to be tuned to a smaller inductance tap on the secondary winding of the output transformer, which is the loading coil. This would improve the efficiency of the transmitter. The certification issue was already discussed. Rangemaster would need to design a fatter antenna for the AM 1000, and re-certify, in order to make the larger diameter antenna legal.
IIRC, and I've looked at several different history threads, the FCC considers that the 3m antenna length does not include the wire in a base loading coil, but concerning a hat, it does include the length of a top hat radial, IOW, the length of the vertical plus the radius of a flat top hat.
Even though the function is capacitive, it does have the potential to increase radiation by building more output power, i.e., it helps prevent losses as the signal goes up the vertical. Of course, it's also different than ground radials.
I would think that in a normal land-based environment, if it weren't for the restriction mentioned above, the combination of ground radials and capacitive hat could do two things for a given signal strength:
1) Decrease the number and length of ground radials.
2) Decrease the height of the vertical antenna component.
That is, if you have a height restriction, such as you have in close proximity to airport landing patterns, along with limited property boundaries at the base of the antenna, then you could still have similar signal strength to a system with more/longer ground radials and increased height with no hat.
The best example for lower power stations may be the old-style LF NDB systems at airports. Because of the nature of our local airport, they recently replaced one here ("FHR" @ 284kHz) and I became interested in the old one, so I checked it all out. It is 50 ft. high triangular tower with 12 buried ground radials 30ft. each, and 6 capacitive hat radials about 5 ft each. The TX puts out 25 watts, and an ADF in an average aircraft can pick it up reliably from at least 30 miles out.
When this thread began I thought capacitance hats were mythical, but the extremely detailed discussion has converted me into a believer.
Does anyone think there is an ideal design for a capacitance hat, such as a shape, or a particular proportion in comparison to the vertical part?