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

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

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.

Might I suggest electric fence wire, a 1/4 mile spool is under $8.00. 19 AWG
and designed for outdoor use.

I have used cage dipoles for years and it has worked well for me. I normally
use 6 wires and slices of 12" diameter plastic sewer pipe cut to 1/4 inch
thickness and 6 holes drilled every 60 degrees(slightly larger than your
wire). on 80 meters I use 4 rings per side equally spaced. the rings are
held in place by winding a short piece of wire around the plastic and
twisting it on each side of the ring to the antenna element.



"SpamLover" wrote in message
om...
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.

What kind of bandwidth do you get with that?

Bob AD3K

w4jle wrote:
Might I suggest electric fence wire, a 1/4 mile spool is under $8.00. 19 AWG
and designed for outdoor use.

I have used cage dipoles for years and it has worked well for me. I normally
use 6 wires and slices of 12" diameter plastic sewer pipe cut to 1/4 inch
thickness and 6 holes drilled every 60 degrees(slightly larger than your
wire). on 80 meters I use 4 rings per side equally spaced. the rings are
held in place by winding a short piece of wire around the plastic and
twisting it on each side of the ring to the antenna element.