On Wed, 06 Apr 2005 02:52:41 GMT, "Dale Parfitt"
wrote:


"Tom Holden" wrote in message
. ..
"Max Power" wrote in message
...
Has anyone ever designed a SW transmission system using curtain arrays
that has a beamwidth of 2.5 to 5 degrees?
Most standard curtain arrays [HR 4/4/1 to 12/6/1] have 15 to 30 degrees
of
beamwidth.

It's gonna be big! A 3 meter diameter dish at 4 GHz has a beanwidth of
1.75
degrees. Scale that to 4 MHz and it will need a diameter of 3 kilometers.
For 5 degree beamwidth, probably about 1 kilometer diameter for 4 MHz, and
400 meter diameter at 10 MHz. An array will have similar dimensions for
similar results.

Tom

An excellent analogy Tom. Narrower beamwidths come about as a result of
increased gain. Increased gain comes from larger arrays.
Those kinds of beamwidths are practical at microwave freqs, not HF.
The gain of the 1M dish (2.5 degree conical beamwidth) at 4 GHz is around
40dBi. A rough esrtimate tells me an array of 4000-8000 1 wavelength dipoles
could achieve this.
Then again, I could be wrong.
Dale W4OP


Well, our Telefunken curtain arrays have a typical gain of 20-23 dB.

TeleSource has just installed two TCI (Technology for Communications
International) 611VS curtains at 270 and 305 degrees for the low band
(6-12 MHz) here on Tinian. 3db azimuthal beamwidth is variable between
20-36 degrees, and they are vertically slewable in 4x4 and 4x6 mode.
Gain is between 16.6 to 24.1 dBi, and tower height is about 470 feet.

I would daresay if a 3-5 degree beamwidth had ever been made, it is
probably experimental. The physical size makes it prohibitively
expensive as well as mechanically improbable.

Al in CNMI
IBB Station engineer (contract)

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