On Sat, 15 Sep 2007 19:16:39 -0700, wrote:

I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these at http://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

Hello Bill,

I can understand that the coax dipoles you built are somewhat more broadbanded than a simple dipole. However,
I suspect that you are unaware of the reason for the broadbanding. Sorry to tell you, but it is achieved only
by the resistive losses in the coax, and not by the reactance obtained by the two sections of shorted coax, as
incorrectly stated in several published articles.

I have made extensive measurements and calculations that prove my statement above. I have reported these
measurements and calculations in both QST and in my book 'Reflections'. The QST reference appears in the
Technical Correspondence, September 1976 issue, and in Chapter 18 in Reflections. You can read Chapter 18 from
my web page at www.w2du.com.

On the other hand, realistic broadbanding, without the loss introduced by the resistances in the coaxial
dipole, can be obtained by the 'cage' dipole, using several parallel wires separated by spacers, as mentioned
other posts appearing in this thread.

Walt, W2DU

Hello Bill,

I can understand that the coax dipoles you built are somewhat more
broadbanded than a simple dipole. However,
I suspect that you are unaware of the reason for the broadbanding. Sorry
to tell you, but it is achieved only
by the resistive losses in the coax, and not by the reactance obtained by
the two sections of shorted coax, as
incorrectly stated in several published articles.

I have made extensive measurements and calculations that prove my
statement above. I have reported these
measurements and calculations in both QST and in my book 'Reflections'.
The QST reference appears in the
Technical Correspondence, September 1976 issue, and in Chapter 18 in
Reflections. You can read Chapter 18 from
my web page at www.w2du.com.

On the other hand, realistic broadbanding, without the loss introduced by
the resistances in the coaxial
dipole, can be obtained by the 'cage' dipole, using several parallel wires
separated by spacers, as mentioned
other posts appearing in this thread.

Walt, W2DU

Hi Walt et al,
I was going to point out the same flawed thinking. I believe Frank Witt also
published the analysis for the flawed reasoning of the bazooka stubs
correcting for the reactance of the dipole off resonance. He also published
coaxial stub designs that did work in QST and several of the ARRL compendia.
It is amazing to me that the bazooka is still used given the alternatives.
One sight where thay are sold claims more gain too!

Dale W4OP

"Dale Parfitt" wrote in message
news:k7jHi.550$6o2.304@trnddc05...

Hello Bill,

I can understand that the coax dipoles you built are somewhat more
broadbanded than a simple dipole. However,
I suspect that you are unaware of the reason for the broadbanding. Sorry
to tell you, but it is achieved only
by the resistive losses in the coax, and not by the reactance obtained by
the two sections of shorted coax, as
incorrectly stated in several published articles.

I have made extensive measurements and calculations that prove my
statement above. I have reported these
measurements and calculations in both QST and in my book 'Reflections'.
The QST reference appears in the
Technical Correspondence, September 1976 issue, and in Chapter 18 in
Reflections. You can read Chapter 18 from
my web page at www.w2du.com.

On the other hand, realistic broadbanding, without the loss introduced by
the resistances in the coaxial
dipole, can be obtained by the 'cage' dipole, using several parallel
wires separated by spacers, as mentioned
other posts appearing in this thread.

Walt, W2DU

Hi Walt et al,
I was going to point out the same flawed thinking. I believe Frank Witt
also published the analysis for the flawed reasoning of the bazooka stubs
correcting for the reactance of the dipole off resonance. He also
published coaxial stub designs that did work in QST and several of the
ARRL compendia.
It is amazing to me that the bazooka is still used given the alternatives.
One sight where thay are sold claims more gain too!

Dale W4OP


Hello Walt, Dale, et al

I thought we worked this out years ago.
The parallel-resonant network of the stubs lowers the SWR some very near
resonance by oscillating at the driven frequency and storing the small
amount of energy that would be reflected back otherwise, but a driven
circuit won't oscillate very far from resonance, and it does nothing for
bandwidth. That's due to loss, as Walt proved long ago. Increasing the
diameter of the radiator, as Walt pointed out, does work. There was a good
recent QST article on just such an antenna.

73
H.
NQ5H