A patch antenna is also a good choice, suggest a sprical package ( basket ball shaped) so that the wind has less effect on the package. QHA does have circular polorized side lobes, but the patch antenna is only 1/4 inch thick, has better axial ratio, better gain and the reflector can be part of the package.
Art, KC6UQH ----- Original Message ----- From: "i8cvs" [email protected] To: "Jeff Kelly" [email protected]; "AMSAT-BB" [email protected] Sent: Saturday, May 05, 2007 8:22 AM Subject: [amsat-bb] Re: Q. for antenna experts!
----- Original Message ----- From: "Jeff Kelly" [email protected] To: [email protected] Sent: Saturday, May 05, 2007 1:14 PM Subject: [amsat-bb] Q. for antenna experts!
On another list for High Altitude Balloons a question came up on installing an 802.11 system on board and what antenna would be best on the balloon.
Hi Jeff, KT2K
On board of the High Altitude Balloon the best circularly polarized antenna for 2.4 GHz is the Quadrifilar Helix Antenna or QHA Look please at the AMSAT Journal May/June 2004 page 6 to 10 for details to build it.
Circular polarization came up.
RHCP on board of Balloon is convenient because the most part of ground stations are already equipped to receive RHCP on 2.4 GHz as they did with AO40
Of course low cost - commercially available was key also.
If you look at the above article you will realize that a Quadrifilar Helix Antenna for 2.4 GHz can be homebrewed at low cost in a few hours of job.
Any suggestions on the balloon side for 2.4?
The Quadrifilar Helix Antenna is very light weight because do not requires a reflector but it radiates a circularly polarized wave all the way towards the earth.
I have seen low cost circular patch antennas for 2.4. Is that a good pattern for up to a 100,000 ft source?
The Quadrifilar Helix Antenna was used on board of OSCAR-7 for the 2304 MHz telemetry Beacon as described in
http://www.w2du.com/r2ch22.pdf
and it's lobe as shown in Fig 22-5 is circularly polarized all the way around the pattern
Guess the balloon side should be LHCP?
The ballon side can be RHCP or LHCP but considering that most radio hams are already using RHCP on the ground then RHCP on the ballon side is preferred.
The balloon payload would be thrown around and spinning in flight.
No problems using a QHA on board of a balloon as depicted in Fig 22-6 and discussed by Walter Maxwell, W2DU in the above article.
Thanks for any ideas.
Jeff KT2K
I hope this helps
73" de
i8CVS Domenico
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