Conical, biconical and discone antennae?
 

"Jeff Liebermann" wrote in message
...



What the military used discones for is receive frequency hopping all
over their HF bands without any band switching or tuning. LDPA (log
periodic) broadband HF antennas were also used, which incidentally was
also present at N6IJ:
www.n6ij.org/antennas.html
Neither antenna had much gain, but they sure had the bandwidth.

--
Jeff
++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++

They were also used for HF transmit on some ships.

Here's a link to an early Navy research paper on the discone/cage
antenna sometimes called a "discage." Unfortunately, only the text
is clear; the pictures are not good.

http://www.navy-radio.com/ant/discage-661464.pdf

Note that a single structure was fed from the top and the bottom by
two separate coax cables.

I had hundreds of inspection and test visits to Navy ships in the 1980s
and 1990s. In practice, I never saw that antenna installed for use
at the extreme low end, as described in the linked paper. There was nearly
always a fan antenna for 2 -6 MHz.

The discone/cage freq ranges were nominally 4 - 12 MHz (cage) and
10- 30 MHz (discone). Both sections were invariably fed through a
multi-transmitter coupler, either four or eight transmitters, depending
on the ship.

I know the fan antennas all had custom matching boxes at the
feed point to bring the SWR within the 3:1 circle. I can't recall if the
sections of the discage also had such matching.

"Sal"
(really KD6VKW)

Conical, biconical and discone antennae?
 

On Mon, 18 May 2015 12:37:14 -0700, "Sal M. O'Nella"
wrote:

They were also used for HF transmit on some ships.

Here's a link to an early Navy research paper on the discone/cage
antenna sometimes called a "discage." Unfortunately, only the text
is clear; the pictures are not good.

http://www.navy-radio.com/ant/discage-661464.pdf

Some photos:
https://www.google.com/search?q=discage+antenna&tbm=isch

I'm not sure, but some of the discage antennas in the photos are more
like fat "cage dipole" or "cage monopole" antennas. The wire cage
increases the effective diameter of the monopole driven element to
increase it's bandwidth.

I couldn't find a better copy of the 1967 Discage paper. Actually,
I've never heard of a discage antenna. My idea of a cage antenna is
the Viet Nam war era "Elephant Cage" direction finder antenna:
https://www.google.com/search?tbm=isch&q=elephant+cage+antenna

Note that a single structure was fed from the top and the bottom by
two separate coax cables.

Not so weird. Visualize a biconical antenna fed as two monopoles from
the narrow pointed ends, instead of being fed as a dipole. Now,
reverse the positions of the biconical elements and we have something
that looks like the discage.

I had hundreds of inspection and test visits to Navy ships in the 1980s
and 1990s. In practice, I never saw that antenna installed for use
at the extreme low end, as described in the linked paper. There was nearly
always a fan antenna for 2 -6 MHz.

I don't have any Navy experience but I can see why a fan antenna was
popular. It's simple, fairly easy to install, and you can cut
elements randomly and still have a working antenna. Best of all, it
doesn't eat deck or turret space.

The discone/cage freq ranges were nominally 4 - 12 MHz (cage) and
10- 30 MHz (discone). Both sections were invariably fed through a
multi-transmitter coupler, either four or eight transmitters, depending
on the ship.

I know the fan antennas all had custom matching boxes at the
feed point to bring the SWR within the 3:1 circle. I can't recall if the
sections of the discage also had such matching.

Despite having a fairly broad bandwidth, it's not a perfect or
constant 50 ohms. Unless the radios can tolerate a moderate VSWR (3:1
perhaps?), some kind of tuner might be useful. However, at 3:1 and
with some kind of VSWR controlled tx power reduction, probably the
impedance matching boxes would be sufficient.

Thanks.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Conical, biconical and discone antennae?
 

"Jeff Liebermann" wrote in message
...

major snippage

Despite having a fairly broad bandwidth, it's not a perfect or
constant 50 ohms. Unless the radios can tolerate a moderate VSWR (3:1
perhaps?), some kind of tuner might be useful. However, at 3:1 and
with some kind of VSWR controlled tx power reduction, probably the
impedance matching boxes would be sufficient.

Thanks.

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

This is true. Although automatic systems, called High Frequency Radio
Group, were being introduced about the time I retired, the older, common
transmit multi-couplers always had to be hand-tuned in those by-gone days.
It was a three-step process that I used to do occasionally. I'm assuming
coupler drawers must have had some reactive components inside. I never had
one open or bothered to dig out the schematics for any of them.

"Sal"