Question on bi-conical antenna
 

The May 2005 issue of QST had an interesting antenna article on page
33... basically discussing broadband dipoles. I am particularly interested
in the biconical (fan) dipole discussed. It is basically two dipoles
common at the feed point, with a slight divergence out to the ends. I
believe they discussed a spread of 6 feet at the ends for an 80 meter
version.

This antenna may be just what I was looking for to put up on 75M.
Do you antenna experts here on this list have any opionions on this? I
prefer "resonant" antennas fed with coax as opposed to open wire feedline
with tuners, but I would like to be able to operate over the entire 75M
band with my IC746Pro.. Comments?


Ed

Aside from a few errors in the article, (ie: 4*2.8 does not equal 10.2) If
your going to use open wire feed, make the antenna 135 feet. See Cecils
site, Cover all bands and save a bunch of wire.

I have used a number of methods over the years to cover 75/80 with a single
antenna. A 12" diameter cage works well at low heights. I used sections of
12 " sewer pipe cut 3/8" thick and 6 wires coming to a cone at the end.

Reg has a program that shows bandwidth vs. Cage diameter. My practical
results achieved greater band width than predicted by the program. Then
again It was at 30 feet.

Some things that do not work, "the bazooka", dual wires spread less than 15
feet, and any of the antennas that are terminated folded dipoles.

"Ed" wrote in message
. 93.175...


The May 2005 issue of QST had an interesting antenna article on page
33... basically discussing broadband dipoles. I am particularly
interested
in the biconical (fan) dipole discussed. It is basically two dipoles
common at the feed point, with a slight divergence out to the ends. I
believe they discussed a spread of 6 feet at the ends for an 80 meter
version.

This antenna may be just what I was looking for to put up on 75M.
Do you antenna experts here on this list have any opionions on this? I
prefer "resonant" antennas fed with coax as opposed to open wire feedline
with tuners, but I would like to be able to operate over the entire 75M
band with my IC746Pro.. Comments?


Ed

Some things that do not work, "the bazooka", dual wires spread less
than 15 feet, and any of the antennas that are terminated folded
dipoles.


Fred, I appreciate your comments on my questions. Could you elaborate on
your statement (above) that "dual wires spread less than 15 feet" do not
work? The QST article, Table 1, seems to indicate they do work, with a
spread of only 6 feet, or even 3 feet, for 75M dipoles.


Ed K7AAT

Reg has a program that shows bandwidth vs. Cage diameter. My
practical
results achieved greater band width than predicted by the program.
Then
again It was at 30 feet.

=================================

My program, DIPCAGE2, is concerned with the bandwidth of a cage dipole
in isolation.

But the type and length, in wavelengths, of the feedline has a
considerable effect on the bandwidth of the radiating SYSTEM as a
whole. And a tuner, if used, also plays a part.

It is not surprising that practical measurements made from the shack
randomly indicate somewhat different bandwidths. But neverthless the
bandwidth of the antenna itself, as predicted by the program, plays
the principal part.

In general, the bandwidth of an antenna does not increase in
proportion to its efective diameter so much as is often fondly
expected. But it is not a critical performance characteristic.
----
Reg, G4FGQ

Reg, I was not impuning your program. I used it as a guide and found that it
followed my actual findings once I scaled the results for my particular
location.

My point was that at the heights most of us "mere mortal" hams are able to
achieve, one can cover 75 meters with a 12" diameter cage.


"Reg Edwards" wrote in message
...
Reg has a program that shows bandwidth vs. Cage diameter. My
practical
results achieved greater band width than predicted by the program.
Then
again It was at 30 feet.

=================================

My program, DIPCAGE2, is concerned with the bandwidth of a cage dipole
in isolation.

But the type and length, in wavelengths, of the feedline has a
considerable effect on the bandwidth of the radiating SYSTEM as a
whole. And a tuner, if used, also plays a part.

It is not surprising that practical measurements made from the shack
randomly indicate somewhat different bandwidths. But neverthless the
bandwidth of the antenna itself, as predicted by the program, plays
the principal part.

In general, the bandwidth of an antenna does not increase in
proportion to its efective diameter so much as is often fondly
expected. But it is not a critical performance characteristic.
----
Reg, G4FGQ

Maybe I misunderstood the point below, but it looked to me, from examining
the empirical data presented in the article, that a spread of 6 feet did a
decent job of broadening the swr curve of a 75/80 m dipole.

If 6' worked so well in the article, why are you saying "dual wires spread
less than 15'" as something that "doesn't work" ? Are you discussing
something else?

....hasan, N0AN

"Fred W4JLE" wrote in message
...

Some things that do not work, "the bazooka", dual wires spread less than
15
feet, and any of the antennas that are terminated folded dipoles.

Ed, this comes from years of practical experience in trying to achieve a
broad antenna.

With all due respect to the various "NEC" programs as well as Reg's program,
they are great for comparing antennas. In the real world environment of most
hams, results do not agree with the predicted on 75.

Why?, because few of us can get a 75 meter antenna any where near a half
wave length high and in the clear. While one may be able to model the real
antenna environment, I am not smart enough. I would suggest that you model
your particular 75 meter antenna, and then measure actual results as a fun
exercise.

Now to the original question, in spite of the data in QST, I have found
spreads of less than 15 feet in a practical environment will not achieve
your goal. YMMV.

We have got to the point in ham radio, we are measuring with a micrometer,
marking with a crayola, and cutting with an axe. I doubt that anyone in the
history of the world has calculated a 75 meter dipole, put it up, and made
no adjustments unless they mis-measured.


Heck for years we have used 468/F to cut our antennas and that is incorrect
as well! Don't rob yourself of the fun of trying something based on a
program. Last night, for example, I had an enjoyable ragchew with a fellow
in England, running my barefoot Icom 706 MKIIG on 75. My antenna is 40 feet
up at it's highest point. Anecdotal evidence for sure, but the QSO was fun
anyway!

Sorry to get so long winded... Good luck on your broad antenna experiments,
the journey is the fun part.

73 Fred W4JLE




"Ed" wrote in message
. 93.175...


Some things that do not work, "the bazooka", dual wires spread less
than 15 feet, and any of the antennas that are terminated folded
dipoles.


Fred, I appreciate your comments on my questions. Could you elaborate
on
your statement (above) that "dual wires spread less than 15 feet" do not
work? The QST article, Table 1, seems to indicate they do work, with a
spread of only 6 feet, or even 3 feet, for 75M dipoles.


Ed K7AAT

Dear W4JLE:

Please expand on the paragraph shown below. Sewer pipe is most often,
hereabout, made of cast iron. What is your pipe made of? How thick is it?
(I assume that the 3/8" mentioned is the height of pieces of pipe that were
used as wire spacers.) How many short sections of pipe did you use?

Thanks, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Fred W4JLE" wrote in message
...
snip

I have used a number of methods over the years to cover 75/80 with a
single
antenna. A 12" diameter cage works well at low heights. I used sections of
12 " sewer pipe cut 3/8" thick and 6 wires coming to a cone at the end.

snip

Just information gained from experiments to achieve a broad 75 meter antenna
in my particular antenna environment.

"hasan schiers" wrote in message
...
Maybe I misunderstood the point below, but it looked to me, from examining
the empirical data presented in the article, that a spread of 6 feet did a
decent job of broadening the swr curve of a 75/80 m dipole.

If 6' worked so well in the article, why are you saying "dual wires spread
less than 15'" as something that "doesn't work" ? Are you discussing
something else?

...hasan, N0AN

"Fred W4JLE" wrote in message
...

Some things that do not work, "the bazooka", dual wires spread less than
15
feet, and any of the antennas that are terminated folded dipoles.

They make a 12" PVC pipe. I got some scrap sections from the guy who put in
sewer lines in my town.

The pipe is cut in such a way that you have rings 12" in diameter and 3/8"
wide. Holes are drilled every 60 degrees. I use 5 rings on each end (10
total). The wires are tied together at the center and end insulators.

I normally tie a wire between a tree and the hitch on my pickup with the 5
rings pre strung. Then add the other 5 wires. Once the whole mess is put
together slide the rings an equal distance apart. The ones at the ends
should be 18 inches from each insulator. Use 6 inch pieces of wire to anchor
the rings. Wrap a couple of inches around the wire, over the top of the ring
and continue wrapping on the wire. 3 per ring works well. Being cheap and as
this antenna uses a LOT of wire I make mine out of electric fence wire (1/4
mile for $7.00). Get some help holding the ends as you raise it. If not you
will end up with the worlds biggest "slinky".

"J. Mc Laughlin" wrote in message
...
Dear W4JLE:

Please expand on the paragraph shown below. Sewer pipe is most often,
hereabout, made of cast iron. What is your pipe made of? How thick is
it?
(I assume that the 3/8" mentioned is the height of pieces of pipe that
were
used as wire spacers.) How many short sections of pipe did you use?

Thanks, Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Fred W4JLE" wrote in message
...
snip

I have used a number of methods over the years to cover 75/80 with a
single
antenna. A 12" diameter cage works well at low heights. I used sections
of
12 " sewer pipe cut 3/8" thick and 6 wires coming to a cone at the end.

snip