Re: Turn off AGC when receiving BPSK-1000
You don't have to use a narrow beam antenna with maximum gain on axis. You can always design it with a bowl-shaped pattern that increases gain toward the edges and lowers it in the middle.
That's why the quadrifilars work so well. I measured the pattern some time back, and the "beam width" is about 140 degrees....
Point them straight up and be satisfied with that part of a pass, or mount them at 40 degrees, and rotate AZ with a TV rotor for the entire pass. For 50 degree max passes point them at the center of the pass...
73, Dave, WB6LLO dguimon1@san.rr.com
Disagree: I learn....
Pulling for P3E...
On 8/18/11 10:31 PM, Dave Guimont wrote:
That's why the quadrifilars work so well. I measured the pattern some time back, and the "beam width" is about 140 degrees....
Yes, something with that kind of beamwidth would be ideal on the nadir-facing surface of a stabilized satellite in low earth orbit. It would be even better if the gain in the straight-down direction could be reduced in favor of gain at the edges. Ideally you'd have a constant power density over the entire visible earth.
You could of course use a much more directional antenna on the ground if it can track the satellite.
--Phil
Phil,
If you have access to the December 1970 issue of the Microwave Journal there is data on a 1 wavelength, 1 turn Quadrifilar Helix with a beam width of greater than 180 degrees. Only the 1/2 turn 1/2 wave is popular today, the 140 degree beam with offers the best front to back ratio @ 0.3 axial wavelengths. Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Phil Karn Sent: Thursday, August 18, 2011 10:44 PM To: Dave Guimont Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: Turn off AGC when receiving BPSK-1000
On 8/18/11 10:31 PM, Dave Guimont wrote:
That's why the quadrifilars work so well. I measured the pattern some time back, and the "beam width" is about 140 degrees....
Yes, something with that kind of beamwidth would be ideal on the nadir-facing surface of a stabilized satellite in low earth orbit. It would be even better if the gain in the straight-down direction could be reduced in favor of gain at the edges. Ideally you'd have a constant power density over the entire visible earth.
You could of course use a much more directional antenna on the ground if it can track the satellite.
--Phil
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Dave, Phil and Bob,
For additional information read
http://www.w2du.com/r2ch22.pdf
and look at Fig 22-7 page 10 of 20 Radiation Pattern of the 1 1/2 turn 1,25 wavelenght Quadrifilar Antennas.
With the antenna straight up pointed to Zenith the gain is 4 dBi all around the azimuth at 30° elevation and -3 dBi overhead at 90° elevation.
73" de
i8CVS Domenico
----- Original Message ----- From: "Dave Guimont" dguimon1@san.rr.com To: "Phil Karn" karn@philkarn.net; "Bob Bruninga" bruninga@usna.edu Cc: amsat-bb@amsat.org Sent: Friday, August 19, 2011 7:31 AM Subject: [amsat-bb] Re: Turn off AGC when receiving BPSK-1000
You don't have to use a narrow beam antenna with maximum gain on axis. You can always design it with a bowl-shaped pattern that increases gain toward the edges and lowers it in the middle.
That's why the quadrifilars work so well. I measured the pattern some time back, and the "beam width" is about 140 degrees....
Point them straight up and be satisfied with that part of a pass, or mount them at 40 degrees, and rotate AZ with a TV rotor for the entire pass. For 50 degree max passes point them at the center of the
pass...
73, Dave, WB6LLO dguimon1@san.rr.com Disagree: I learn.... Pulling for P3E...
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
For additional information read
http://www.w2du.com/r2ch22.pdf
and look at Fig 22-7 page 10 of 20 Radiation Pattern of the 1 1/2 turn 1,25 wavelenght Quadrifilar Antennas.
Tnx, Dom for that info.
I received a number of requests for quadfilar information, again.
Goto
http://cid-1973adc8c1d3207c.skydrive.live.com/summary.aspx?sa=140581470 and see the five files starting with the pic Quad2.4gigs
Be very precise with the measurements, particularly on the 435... I scaled it from the 2 meter, made a slight measuring error on the driven filar, shortened it by 1/4" and the swr went from 3 to 1 to 1.6 to 1....
And use the BEST "N" connectors and coax that you can find, the most expensive part of the antenna....
73, Dave, WB6LLO dguimon1@san.rr.com
Disagree: I learn....
Pulling for P3E...
participants (4)
-
Art McBride -
Dave Guimont -
i8cvs -
Phil Karn