Reg, G4FGQ wrote:
"Richard, If you got this off Terman and Kraus then Terman and Kraus are
a couple of the oldest of old wives."

I can`t blame them because I wrote without consulting them first.

Terman does in fact say about what I said. I haven`t checked with Kraus
yet. In his 1955 edition on page 921 Terman writes:
"The second possible way to achieve broad-band characteristics consists
in starting with a resonant antenna (as opposed to a rhombic for
example), but so proportioning this antenna as to minimize resonance
effects. Thus a resonant antenna employing a thin wire is equivalent to
a moderately high Q system and so has a relatively narrow frequency
band.
However, if the diameter of the antenna is made large, the effective Q
is very substantially reduced with resulting increase in bandwidth."

Best regards, Richard Haarrison, KB5WZI

I also wrote:
"Fat antennas have more bandwidth, and that is inversely proportional to
Q. Reducing antenna Q, by fattening the antenna, reduces the antenna
potential by almost the same factor."

Here is support from Ed Laport`s "Radio Antenna Engineering page 37":
"It is seen that bandwidth is inversely proportional to antenna (or
total circuit) Q. To decrease Q, the same design considerations are
required as for the reduction of antenna potential."

Best regards, Richard Harrison, KB5WZI

As a competent and experienced engineer, it should then be simple for
you to answer the following:

What is the gain difference, in dB, between a dipole resonant at 97.5
MHz (the geometric center of the FM band) which is 1 mm diameter and one
which is 1 cm diameter? Feel free to assume that the conductor is
perfect, or use copper if you prefer.

Also feel free to calculate the antenna Q and "antenna potential",
although the question here is about gain.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"That`s interesting.(I don`t know why you want fat. It will give you
lower gain.) How much lower? Why?"

It`s a fact. Fat antennas have more bandwidth, and that is inversely
proportional to Q. Teducing antenna Q, by fattening the antenna, reduces
the antenna potential by about the same factor.

Best regards, Richard Harrison, KB5WZI

On Mon, 31 Jan 2005 15:14:49 -0800, Roy Lewallen
wrote:

As a competent and experienced engineer, it should then be simple for
you to answer the following:

What is the gain difference, in dB, between a dipole resonant at 97.5
MHz (the geometric center of the FM band) which is 1 mm diameter and one
which is 1 cm diameter? Feel free to assume that the conductor is
perfect, or use copper if you prefer.

Also feel free to calculate the antenna Q and "antenna potential",
although the question here is about gain.

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"That`s interesting.(I don`t know why you want fat. It will give you
lower gain.) How much lower? Why?"

It`s a fact. Fat antennas have more bandwidth, and that is inversely
proportional to Q. Teducing antenna Q, by fattening the antenna, reduces
the antenna potential by about the same factor.

Best regards, Richard Harrison, KB5WZI


Hi Roy,

What an unusual demand to throw in the face of someone who agrees with
you: no difference in gain. Richard's quote is merely your ironic
question to Buck's quote (already discounted by Buck).

However, for Brad's interest (and conforming to his original design,
not of 1cM but more like 170mm diamter) the Q for the fatter dipole is
indeed much less (in fact it covers the entire FM band into a 50 Ohm
load between 2:1 VSWR points) where the thin dipole (1mm) is something
less than 6MHz. Bandwidth (and inferentially Q) differential 4:1
which would translate the input V to the tips to something less (at
the same proportion) than that experienced with the thin dipole (which
for a recieve antenna is a strange characteristic to focus upon).

73's
Richard Clark, KB7QHC

I dont know where YOU got your antenna info from....but just because a
dipole has wide b/w (low Q) does not lower its gain unless the diameter of
the dipole causes the resonant length to be much shorter than 1/2
wavelength...but in practical terms, that wont happen (unless he makes the
dipole out of 4 ft pipe for instance!

A wide b/w (fat) dipole made for 80m (a cage dipole) does not have any less
signal strength than a single wire dipole (2.15 dbi).....sorry.

Chris
WB5ITT
PG-9-5322 FCC Commercial
Telecom/Broadcast engineer for 30 years

"Richard Harrison" wrote in message
...
Roy, W7EL wrote:
"That`s interesting.(I don`t know why you want fat. It will give you
lower gain.) How much lower? Why?"

It`s a fact. Fat antennas have more bandwidth, and that is inversely
proportional to Q. Teducing antenna Q, by fattening the antenna, reduces
the antenna potential by about the same factor.

Best regards, Richard Harrison, KB5WZ

CWB wrote:
I dont know where YOU got your antenna info from....but just because a
dipole has wide b/w (low Q) does not lower its gain unless the diameter of
the dipole causes the resonant length to be much shorter than 1/2
wavelength...

Here's a quiz question: Suppose the dipole could be made fat enough to
reduce the resonant length to 0.01 wavelength. How much would the gain
be reduced?

Part 2: Suppose the dipole remained the same diameter and was reduced in
length to 0.01 wavelength. If the conductor were perfect, how much would
the gain be reduced?

Hint for Part 2: This is easily answered using the free EZNEC demo
program, another modeling program of your choice, or a few minutes'
reading of just about any antenna textbook.

Roy Lewallen, W7EL

From URL:
http://www.astronantennas.com/polarization.html
In the early days of FM radio in the 88-108 MHz spectrum, the radio stations
broadcasted horizontal polarization. However, in the 1960's, FM radios
became popular in automobiles which used vertical polarized receiving whip
antennas. As a result, the FCC modified Part 73 of the rules and
regulations to allow FM stations to broadcast RHC or elliptical polarization
to improve reception to vertical receiving antennas as long as the
horizontal component was dominant.
--
Caveat Lector


Someone correct me, but don't FM stations transmit both vertical and
horizontal?

I hope this helps.


--
73 for now
Buck
N4PGW

On Mon, 31 Jan 2005 06:28:37 -0800, "Caveat Lector"
wrote:

From URL:
http://www.astronantennas.com/polarization.html
In the early days of FM radio in the 88-108 MHz spectrum, the radio stations
broadcasted horizontal polarization. However, in the 1960's, FM radios
became popular in automobiles which used vertical polarized receiving whip
antennas. As a result, the FCC modified Part 73 of the rules and
regulations to allow FM stations to broadcast RHC or elliptical polarization
to improve reception to vertical receiving antennas as long as the
horizontal component was dominant.

Thanks Caveat Lector.

(Caveat emptor means buyer beware, what does caveat lector mean?)


--
73 for now
Buck
N4PGW

Reader Beware -- hi hi

I have had some awful experiences on the NG's using my real identity and
Amateur Radio call sign -- so thought Caveat Lector was appropriate for the
NG's

73 -- Caveat Lector



"Buck" wrote in message
...
On Mon, 31 Jan 2005 06:28:37 -0800, "Caveat Lector"
wrote: From URL:
http://www.astronantennas.com/polarization.html
In the early days of FM radio in the 88-108 MHz spectrum, the radio
stations
broadcasted horizontal polarization. However, in the 1960's, FM radios
became popular in automobiles which used vertical polarized receiving whip
antennas. As a result, the FCC modified Part 73 of the rules and
regulations to allow FM stations to broadcast RHC or elliptical
polarization
to improve reception to vertical receiving antennas as long as the
horizontal component was dominant.

(Caveat emptor means buyer beware, what does caveat lector mean?)
--
73 for now
Buck
N4PGW

On Mon, 31 Jan 2005 10:54:43 -0500, Buck wrote:

(Caveat emptor means buyer beware, what does caveat lector mean?)

Hi Buck,

You got the Caveat part down, but I'm not sure if ***** is being coy,
or has taken the wrong translation. His intent may be (if read
literally) that "reader beware." However, this is not the same as the
meaning of lector, where the meaning would offer "beware reader." It
is a subtle distinction at best leading to the same caution, but
Lector is one who reads (imparts information) to others (instead of
being a silent reader, such as anyone "reading" this post).

73's
Richard Clark, KB7QHC