Best Books/Websites for Antenna Theory and Building Recommendations
 

"Cecil Moore":
Jimmie D wrote:
One such mistake is calling a 4 ft long antenna that has a coil to make
it resonate on the 10M band a "10M loaded 1/4 wavelength antenna".

They should be more careful and specify that they are
talking about electrical lengths, not physical lengths.
______________

They also should point out that, although a radiator physically/electrically
shorter than needed for first self-resonance can be "loaded" to resonance,
this does not mean that loaded and self-resonant radiators perform equally
well in an installed system. In some applications there can be as much as a
100:1 difference in their radiated powers, for a given power at the
transmitter output connector.

RF

Best Books/Websites for Antenna Theory and Building Recommendations
 

Richard Fry wrote:
"Cecil Moore":
Jimmie D wrote:
One such mistake is calling a 4 ft long antenna that has a coil to
make it resonate on the 10M band a "10M loaded 1/4 wavelength antenna".

They should be more careful and specify that they are
talking about electrical lengths, not physical lengths.

They also should point out that, although a radiator
physically/electrically shorter than needed for first self-resonance can
be "loaded" to resonance, this does not mean that loaded and
self-resonant radiators perform equally well in an installed system. In
some applications there can be as much as a 100:1 difference in their
radiated powers, for a given power at the transmitter output connector.

Good point, Richard. An antenna's ability to "load"
is proportional to its electrical length. An antenna's
ability to radiate seems to be proportional to the
physical length of the antenna that is carrying the
highest current. In 75m shootouts, the mobile antennas
with the loading coil furtherest away from the feedpoint
(closest to top-loaded) generally won the shootout.
--
73, Cecil http://www.w5dxp.com

Best Books/Websites for Antenna Theory and Building Recommendations
 

"Cecil Moore" :
An antenna's abilty to "load"
is proportional to its electrical length. An antenna's
ability to radiate seems to be proportional to the
physical length of the antenna that is carrying the
highest current.
__________

Perhaps unexpectedly, the intrinsic pattern and directivity of a
physically/electrically short, unloaded monopole radiator are not greatly
different than those of a self-resonant 1/4-wave monopole. The big problem
with an unloaded, short radiator is the reactance at its feedpoint, which
means that very little current will flow into the short radiator from any
practical r-f source. But for the current that DOES flow in it, its
radiation performance will not be much different than that of a
self-resonant 1/4-wave monopole, at that same current flow (as NEC will
show).

Using a "loading" reactance to resonate the radiator allows maximum power
transfer from the r-f source into the feedpoint. But the remaining issue is
the low radiation resistance of the short radiator even when it is resonant,
which is a small fraction of the other series resistances in the antenna
system (ground and coil loss, mostly). As a result, much of the available
transmitter power produces heat rather than EM radiation.

RF

Best Books/Websites for Antenna Theory and Building Recommendations
 

"Richard Fry" wrote in message
...
"Cecil Moore" :
An antenna's abilty to "load"
is proportional to its electrical length. An antenna's
ability to radiate seems to be proportional to the
physical length of the antenna that is carrying the
highest current.
__________

Perhaps unexpectedly, the intrinsic pattern and directivity of a
physically/electrically short, unloaded monopole radiator are not greatly
different than those of a self-resonant 1/4-wave monopole. The big
problem with an unloaded, short radiator is the reactance at its
feedpoint, which means that very little current will flow into the short
radiator from any practical r-f source. But for the current that DOES
flow in it, its radiation performance will not be much different than that
of a self-resonant 1/4-wave monopole, at that same current flow (as NEC
will show).

Using a "loading" reactance to resonate the radiator allows maximum power
transfer from the r-f source into the feedpoint. But the remaining issue
is the low radiation resistance of the short radiator even when it is
resonant, which is a small fraction of the other series resistances in the
antenna system (ground and coil loss, mostly). As a result, much of the
available transmitter power produces heat rather than EM radiation.

RF I had an electronics instructor (not sure what he knew about antennas)
say thet there was a 10/90 rule about antennas. That an antenna 10 % as
long as a 1/4 wl will radiate 90%as well, wile he didnt say it I assume
this means with all other sources of loss minimized. Is this anywhere near
true?
/Jimmie

Best Books/Websites for Antenna Theory and Building Recommendations
 

"Jimmie D":
RF I had an electronics instructor (not sure what he knew about antennas)
say thet there was a 10/90 rule about antennas. That an antenna 10 % as
long as a 1/4 wl will radiate 90%as well, wile he didnt say it I assume
this means with all other sources of loss minimized. Is this anywhere near
true?
_____________

Theoretically yes, but not so much in practice.

Without losses, an "infinitesimally short" linear dipole has 91% of the
peak directivity of a self-resonant 1/2-wave dipole (1.5 vs 1.64). And
for a given applied power both of them would radiate the same total amount
of power, just with marginally different pattern shapes.

The problem is that system losses in a real, "loaded" short antenna can be
much higher than the radiation resistance, so a loaded short antenna may not
radiate much of the available power -- in some applications not even 1% of
it.

RF

Best Books/Websites for Antenna Theory and Building Recommendations
 

"Joaquin Tall" wrote in message
...
Hello All,

I have just gotten my tech license and am eager to get my station up and
running. I am starting on a shoestring; currently, I have no equipment
whatsoever and don't know what I should buy just yet. In absence of a
rig, I am now studying to pass my General license exam next month.

I am very interested in building my own HF/VHF/UHF antennas. I've seen
the ARRL books, but I was hoping that you good folks might have some
favorite websites, book titles or magazine issues [old or new] that
you'd be willing to pass along that could get me started.

I will make my (usual) pitch for the j-pole antenna.

Take a look at http://www.hamuniverse.com/jpole.html and see what can be
done at UHF/VHF with a few pieces of pipe, some solder and a torch. The
j-pole is a good match after a little fiddling, It's durable, requires no
ground plane and can be mounted almost anywhere. I have made about two
dozen of them for myself, for RACES and for friends in the local club. My
first one (early 90's) is on the roof of my house and I used it on 2m
earlier this evening, as I do most evenings.

Search google.com for jpole antenna and see about 40,000 other links.

The "quad antenna" and its cousin the "quagi," a quad/yagi hybrid, are also
possible, but I've never built any of them, myself. The venerable
whip-over-downward-radials is easy but can be tedious to tune for a good
match. (I built one of them onto a construction hardhat as an novelty; got
a good match, too.)

I'm next door to you in Chula Vista, by the way.

KD6VKW
http://members.cox.net/sobars/

Best Books/Websites for Antenna Theory and Building Recommendations
 

On Tue, 6 Feb 2007 20:55:54 -0800, "Sal M. Onella"

Don't ever sell the good ol' Di-Pole short! Besides being CHEAP,
it's easy to set up and take down, and not too annoying to the
neighbors ether.

If you got one set up, you can sling a wire under it and turn it
into a "Cloud Warmer", and that has a whole lot of interesting
possibility right there too.

73's
FFF




wrote:


"Joaquin Tall" wrote in message
.. .
Hello All,

I have just gotten my tech license and am eager to get my station up and
running. I am starting on a shoestring; currently, I have no equipment
whatsoever and don't know what I should buy just yet. In absence of a
rig, I am now studying to pass my General license exam next month.

I am very interested in building my own HF/VHF/UHF antennas. I've seen
the ARRL books, but I was hoping that you good folks might have some
favorite websites, book titles or magazine issues [old or new] that
you'd be willing to pass along that could get me started.

I will make my (usual) pitch for the j-pole antenna.

Take a look at http://www.hamuniverse.com/jpole.html and see what can be
done at UHF/VHF with a few pieces of pipe, some solder and a torch. The
j-pole is a good match after a little fiddling, It's durable, requires no
ground plane and can be mounted almost anywhere. I have made about two
dozen of them for myself, for RACES and for friends in the local club. My
first one (early 90's) is on the roof of my house and I used it on 2m
earlier this evening, as I do most evenings.

Search google.com for jpole antenna and see about 40,000 other links.

The "quad antenna" and its cousin the "quagi," a quad/yagi hybrid, are also
possible, but I've never built any of them, myself. The venerable
whip-over-downward-radials is easy but can be tedious to tune for a good
match. (I built one of them onto a construction hardhat as an novelty; got
a good match, too.)

I'm next door to you in Chula Vista, by the way.

KD6VKW
http://members.cox.net/sobars/