Buck wrote:

I don't know why you want FAT. It will give you lower gain. . .

That's interesting. How much lower? Why?

Roy Lewallen, W7EL

On Mon, 31 Jan 2005 02:21:24 -0800, Roy Lewallen
wrote:

It will give you lower gain. . .

What were you thinking?

My apologies to the OP and others.....

I don't know why I said 'lower gain'. (make a note to myself, don't
answer usenet when I should be asleep.)

The fatter dipole will offer a broader bandwidth and a reduced length.
However for the FM broadcast band reception, bandwidth isn't a
problem.

Thanks Roy and Richard. My apologies to you Brad.


--
73 for now
Buck
N4PGW

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

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

===========================
Richard, If you got this off Terman and Kraus then Terman and Kraus are a
couple of the oldest of old wives.
---
Reg

On Mon, 31 Jan 2005 16:55:03 +0000 (UTC), "Reg Edwards"
wrote:

If you got this off Terman and Kraus then Terman and Kraus are a
couple of the oldest of old wives.

Reggie,

This has got to be the height of your boredom to force your nemesis
into the thread to then complain about them. Sounds unmistakably like
the envy of a hausfrau.

73's
Richard Clark, KB7QHC

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

Richard Clark wrote:
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

If you were agreeing with me, Richard (Harrison), I apologize. It wasn't
apparent to me with my poor language skills. Thanks to Richard (Clark)
for effectively applying his superior parsing skills to the problem.

There are only two ways to change the free space gain of an antenna --
change the efficiency, or change the pattern. Those are all the choices
you've got. A fat antenna is certainly no less efficient than a skinny
one -- in fact, it'll be more efficient. But the difference in this case
would be so small as to be unmeasurable. There would be some very slight
change in pattern between a fat antenna and a slim one, but again the
change would be negligibly small.

Considering only free space performance to remove the additional
variable of ground reflection, and assuming that an antenna is
essentially 100% efficient, it's impossible to design an antenna that
has gain in its best direction which is any less than 2.15 dB below that
of a half wave dipole. The lowest possible gain of any efficent antenna
is the isotropic, at 0 dBi.

Roy Lewallen, W7EL