Goal:
* Minimum fuss 3-30MHz operation, mostly on 5-15MHz.
* Will use step-dowm RF transformer between antenna and low impedance
coax
* May use autotuner on TX
* Like the wirecage antennas still today seen on many a military
vessel.

Available on roof:
- 25ft steel structure (like piramid base for power line)
- about 100 feet space in one direction
-...to abandoned flue chimney, 100ft away and 10 feet lower than base
of steel structure
- roof covered with alu plates on tar (could be all arc welded
together, perhaps.

THIS LOOKS PRETTY MUCH LIKE A SHIP TO ME cept its' 120ft aboveground.

I want to build a wire cage monopole
- sloping down from steel tower
- using tower as counterpoise
- feedpoint at top of sloper, via stepdown rf transfomrer, grounded to
tower
- coax cable lead, with rf choke coils and surge suppressors.

Questions:
- what kind of cage antenna?
- how many wires?
- what spreaders, how large?
- ideal wire?

Current plan config:
- length 14 m = 2 x 4m straight sections, + 2 x 3m truncated cubes
- spreaders at 3-7-11 m
- 140 cm dia. spreaders, each made with two waterproofed bamboo
triangles in "star of David" configuration; wire kept parallel at 70cm
distance from each orther.
- material: .8mm copperclad, abt. 90 m (270 ft) total.

Any hints, like more/fewer parallel wires, broader / smaller
spreaders, different materials, dirrerent antenna wire, RF
downtransformer, whatever?

Filippo

SpamLover wrote:

Goal:
* Minimum fuss 3-30MHz operation, mostly on 5-15MHz.
* Will use step-dowm RF transformer between antenna and low impedance
coax
* May use autotuner on TX
* Like the wirecage antennas still today seen on many a military
vessel.

Available on roof:
- 25ft steel structure (like piramid base for power line)
- about 100 feet space in one direction
-...to abandoned flue chimney, 100ft away and 10 feet lower than base
of steel structure
- roof covered with alu plates on tar (could be all arc welded
together, perhaps.

THIS LOOKS PRETTY MUCH LIKE A SHIP TO ME cept its' 120ft aboveground.

I want to build a wire cage monopole
- sloping down from steel tower
- using tower as counterpoise
- feedpoint at top of sloper, via stepdown rf transfomrer, grounded to
tower
- coax cable lead, with rf choke coils and surge suppressors.

Questions:
- what kind of cage antenna?
- how many wires?
- what spreaders, how large?
- ideal wire?

Current plan config:
- length 14 m = 2 x 4m straight sections, + 2 x 3m truncated cubes
- spreaders at 3-7-11 m
- 140 cm dia. spreaders, each made with two waterproofed bamboo
triangles in "star of David" configuration; wire kept parallel at 70cm
distance from each orther.
- material: .8mm copperclad, abt. 90 m (270 ft) total.

Any hints, like more/fewer parallel wires, broader / smaller
spreaders, different materials, dirrerent antenna wire, RF
downtransformer, whatever?

Filippo

Why?

On 29 Oct 2003 15:40:28 -0800, (SpamLover) wrote:

Questions:
- what kind of cage antenna?
- how many wires?
- what spreaders, how large?
- ideal wire?

Hi OM,

http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm

73's
Richard Clark, KB7QHC

Neat! Thanks.

In case it hadn't been mentioned, the cage, with a wire-constructed discone on
top of it, is/was a popular antenna on large US Navy vessels. Called a
discone-discage, it is mounted on the ship's bow. It reminds me of a rhino's
horn.

Bill, K5BY

Questions:
- what kind of cage antenna?
- how many wires?
- what spreaders, how large?
- ideal wire?

Hi OM,

http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm

Ahhhh man, there is this home I pass by at least once or twice a week that
has this antenna on top of his home. I didn't really know what it was, I
do now. :-)

Looks pretty wild to the driver-by

--
^~^~^Monitoring The Spectrum^~^~^~^
*********Hammarlund129X & 140X**********
^^^^^^^^Heathkit Q Multiplier^^^^^^^^^
*~*~++++++GO BEARCATS++++++~*~*~
GE P-780

It's been more than forty years since I'd fooled with a Navy discone-discage
but I seem to remember the cage was used below 10 MHz and the cone, above 10.

Each had a remote controlled couple at its base. There was a remote controlled
tuner at the transmitter end. Of course, the antennas were used for transmit
and receive.

Which reminds me... The third main antenna on the cruiser I worked on was a
standard Navy 33-foot whip, mounted horizontally from the top of the
wheelhouse. It was the radiator or "exciter" and the ship's deck was the
reflector. It worked fine on HF. The distance of the whip above the deck was
quite great. Else I might try that, or similar, by supporting a wire above my
65-foot metal mobilehome. Oh, if I only had the energy these days to still do
things like that.

Bill, K5BY

Thank you Richard!

N8KDV: Why?

Goals:
- single antenna setup
- little or no need for tuner, or at least little need of re-tuning
every 3 kHz
- effective broadband response, i.e. low likelyhood of really dead
spots thru the spectrum
- unlike a T2FD, still very usable on MF/LF for listening using an
ultrabroadband double-transformer impedance adaptor (receive-only
types, confirmed usable for QRP)
- compromises accepted for efficiency, radiation pattern

It is really telling that professional setups hardly ever optimize for
narrowband coverage. The cage-discone is a prime example.

If you trawl the web, you find many examples of very rough "vertical
monopoles", and I have seen they fall into 2 main categories:
- multiple vertical masts (usually 2 or 3), with a symmetrical
horizontal crossbar, fed from a broadband transformer, cold end
grounded to ship deck
- cage designs, either cage-discone or just a huge paunchy
ellipsoid-like cage.

Either way, SWR may wag a little, impedance mismatch is roughly dealt
with by transformer, and a big whocares for rad pattern etc etc. This
is what you need for spreadspectrum, ALE, multiplexing etc. Multi-kW
transmitters help. Some of those commercial military designs are
rated for tens of kW continuous. At most, I'll put 5W into this
thing. Maybe.

Richard, your design seems to favor a lot of parallel wires, but the
big improvement in broadbanding seems to be going from 1 to 2-3 wires.
Does the model confirm that? I have no modeling SW - what do you use?

Also, everyone,

- any hints at to whether wire diameter matters? Commercial antennas
have EITHER lots of wires OR thick masts. Is that out of mechanical
or electrical considerations?

- what are the dimensions of typical HF multiwire monopoles in actual
use on ships?

and

- don't u thing a multiwire cage sloper looks ubercool too?? a real
neighbour-pleaser!

On 30 Oct 2003 00:56:28 -0800, (SpamLover) wrote:


Richard, your design seems to favor a lot of parallel wires, but the
big improvement in broadbanding seems to be going from 1 to 2-3 wires.
Does the model confirm that? I have no modeling SW - what do you use?

Also, everyone,

- any hints at to whether wire diameter matters? Commercial antennas
have EITHER lots of wires OR thick masts. Is that out of mechanical
or electrical considerations?

- what are the dimensions of typical HF multiwire monopoles in actual
use on ships?

and

- don't u thing a multiwire cage sloper looks ubercool too?? a real
neighbour-pleaser!

Hi Filippo,

More wires, smoother passband. Less wires, more mismatches. If you
want one thicker element rather than more wire, it will have to be
roughly the same diameter as the cage presented at my page. No free
lunches at the Maxwell Cafe.

The model is available at that page, you can find a restricted version
of EZNEC at (predictably):
http://www.eznec.com/
It won't allow you to do analysis for this model (unless you cut loose
the $89), but you can view the design and the particulars (like wire
size, length, distance above ground, etc.).

I have a photograph of a pre-WWII battleship sitting above my
workstation here. Within the field of view is a cage dipole end (from
the photographer's perspective of being above the after gun turret, it
is quite close with six wires at a diameter of at least 18 inches).

73's
Richard Clark, KB7QHC

Right!

the big improvement in broadbanding seems to be going
from 1 to 2-3 wires.
Rather, from 1 to a lot of wires OR to 2 or 3 THICK self supporting
masts.

More wires, smoother passband. Less wires, more mismatches.
I have checked a couple of things:

1) Land based cage monopoles. Typically:
- height: .24 lambda at the lowest frequency
- max diameter: .18 lambda at almost half height
- up to 24 / 36 wires
- ground plane with at least 24 wires
- bandwidth easily 7:1

2) Pix of dipoles spotted atop Russian embassies, eyeballed based on
height of balcony railings
- 6 conductors
- spacers approx. 1 m diameter, every 3 m
- poles typically 10-12 m each

If you
No free lunches at the Maxwell Cafe.
Whence the success of the Maxwell House brand.

http://www.eznec.com/
No free lunch there either. The demo only does 20 elements. If I did
an 8-wire cage in decent sized diameter stainless steel rope, it would
set me back in the 100s at my local prices, so I might as well buy the
SW and learn to use it.

The copperclad steel MIG continuous welding wire I was testing has
rusted in ONE NIGHT under the fall rain. I'll look for a source of
stainless welding wire. I have a single wire sloper up for the last 4
years and it looks absolutely new - courtesy of the head of mechanical
maintenance at a cement factory I did consulting at.

The only difference in performance between a cage antenna and an ordinary
thin-wire dipole is a modest increase in bandwidth. There is no increase in
radiating/receiving efficience.

The increase in bandwidth is much less than is popularly supposed and may
not be considered worth the extra construction costs and inconvenience.

To predict resonant frequency, bandwidth and a few other characteristics
from overall length, number of cage wires from 1 to N, and wire diameter,
download program DIPCAGE from website below.

Download DIPCAGE in a few seconds, no unzipping inconvenience, run
immediately.
----
=======================
Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
=======================