On Sun, 23 Nov 2003 16:25:14 -0800, "Michael Melland"
wrote:

Looking for opinions..... seems conventional wisdom indicates a discone.
There are active antennas covering this range too. Any opinions or
recommendations ?

Mike

Hi Mike,

Unless you want to UHF DX Satellites, you might want to consider more
than one size.

73's
Richard Clark, KB7QHC

Get this wideband discone antenna it is a good and antenna and you can
transmitt 200watts with it http://www.grove-ent.com/ANT9.html/

Good Wideband RX Antenna for 25 -1300 MHz ?
 

Looking for opinions..... seems conventional wisdom indicates a discone.
There are active antennas covering this range too. Any opinions or
recommendations ?

Mike

--
Michael Melland, W9WIS
Winneconne, WI USA
http://webpages.charter.net/w9wis

In article , Michael Melland
wrote:

Looking for opinions..... seems conventional wisdom indicates a discone.
There are active antennas covering this range too. Any opinions or
recommendations ?

Mike

Depends on what you're listning to--

You can get a log-periodic to cover that range (Create makes one). You
can go the discone route.

The LP has gain, and needs to be pointed.

The discone doesn't exhibit gain (over isotropic), and the radiation
pattern changes with frequency. In particular, the take-off angle
increases with frequency. If you have 25 MHz as your low point, by the
time you get to 440, the main lobe is going to be around 50 degrees.
Oh, and the discone, along with ground-plane antennas, has a pretty
good null directly vertical from the antenna. Makes it kind of a pain
for satellite work, when your antenna has a sharp null when the bird is
directly overhead!

For info on discones, see for example, the RSGB VHF/UHF manual.
Discones are covered in section 8.37, and log periodics are in section
8.21. The RSGB book gives a lucid explanation of construction if you
want to roll your own, and for 440 MHz and up, that's pretty easy and
pretty small.

I use a pair of discones, one for the lower end of things (50-250 MHz
or so), and a second for the higher end (440-1300 MHz). I also have an
eggbeater (from m2) for 137 and 144 MHz birds.

And don't skimp on the feedline -- LM400 is a good starting point.

--
Namaste-

Bob, K6RTM wrote:
"Discones are covered in section 8.37 and log periodics are covered in
section 8.21."

In my 3rd edition of the RSGB VHF/UHF Manual, the discone is on page
7.28 and the log periodic is on page 7.35.

Bob also wrote:
"The take-off angle increases with the frequency."

In my experience, the vertical angle of maximum radiation, in general,
decreases with antenna height above the earth, when the height of the
antenna in is not over 5/8 wavelength.

Increasing the frequency used with an antenna of fixed height is
equivalent to increasing the height of an antenna using a fixed
frequency because it is a function of antenna height above the
reflecting surface in terms of wavelength. It is all a matter of scale.
At double the frequency, an antenna only needs half the physical height
to be the same elevation above ground to have the same elevation in
terms of wavelength. Soil conductivity and depth of penetration in the
earth are being ignored in the comparison for simplicity. It`s no big
deal.

A 1/2-wave horizontal dipole erected 1/4-wave over good earth has its
maximum radiation toward the zenith. The same antenna elevated to
1/2-wave above the earth has a take-off angle near 30 degrees above the
horizon.

When antenna height exceeds 5/8 wavelength, added lobes appear in the
vertical radiation pattern. The additional lobes appear in the vertical
radiation patterns of vertical antennas too when their heights exceed
5/8-wavelength. It is for this reason that AM broadcast stations usually
limit their towers to no more than 5/8-wavelength. Sky wave propagation
could produce substantial interference with the ground wave signal at
relatively short distances at night from the high-angle radiation.

In a sense Bob is correct in that some of the take-off angle increases
with frequency, in that it produces growth of additional lobes in the
take-off pattern.

Best regards, Richard Harrison, KB5WZI

Richard wrote:
In my experience, the vertical angle of maximum radiation, in general,
decreases with antenna height above the earth, when the height of the
antenna in is not over 5/8 wavelength.

That's a good paraphrase of the standard writings on the subject, but..

Richard also wrote:
A 1/2-wave horizontal dipole erected 1/4-wave over good earth has its
maximum radiation toward the zenith. The same antenna elevated to
1/2-wave above the earth has a take-off angle near 30 degrees above the
horizon.

Please explain this (apparent) contradiction? I expended significant effort
to get a dipole 1/2 wavelength above ground, and did so specifically for
long-haul communications. I may have missed any theory about the 1/4
wavelength being the optimal height, as I was always told (as I read) that
1/2 wavelength height was considered optimal for a number of reasons, not
the least of which was the best take-off angle.

Thanks,

Jack Painter
NF05CM
Oceana Radio

Well, maybe the late hour contributed to MY mix up of Zenith (overhead) and
Azimuth, horizon, etc. Thanks for the nice piece anyway Richard!

"Jack Painter" wrote in message
news:TSBwb.14594$yM6.11303@lakeread06...
Richard wrote:
In my experience, the vertical angle of maximum radiation, in general,
decreases with antenna height above the earth, when the height of the
antenna in is not over 5/8 wavelength.

That's a good paraphrase of the standard writings on the subject, but..

Richard also wrote:
A 1/2-wave horizontal dipole erected 1/4-wave over good earth has its
maximum radiation toward the zenith. The same antenna elevated to
1/2-wave above the earth has a take-off angle near 30 degrees above the
horizon.

Please explain this (apparent) contradiction? I expended significant
effort
to get a dipole 1/2 wavelength above ground, and did so specifically for
long-haul communications. I may have missed any theory about the 1/4
wavelength being the optimal height, as I was always told (as I read) that
1/2 wavelength height was considered optimal for a number of reasons, not
the least of which was the best take-off angle.

Thanks,

Jack Painter
NF05CM
Oceana Radio

Jack Painter wrote:
"I may have missed any theory about the 1/4 wavelength being the optimal
height---."

I missed that too, unless your aim is near vertical incidence reflection
from the ionosphere for nearby contacts. Some hams have that goal and
argue that 1/4-wave height is enough because it gives the first
elevation that produces the drivepoint impedance of the horizontal
dipole in free-space.

The purpose of the antenna is communication, not impedance. A friendly
impedance helps of course.

Best regards, Richard Harrison, KB5WZI

In article ,
Richard Harrison wrote:

Bob, K6RTM wrote:
"Discones are covered in section 8.37 and log periodics are covered in
section 8.21."

In my 3rd edition of the RSGB VHF/UHF Manual, the discone is on page
7.28 and the log periodic is on page 7.35.

Richard--

I'm working with the second edition -- I'll ask Santa for the third
edition, and then figure out which one to keep at home, and which at
the office!

--
Namaste-