[amsat-bb] Re: Q. for antenna experts!

[i8cvs]

----- Original Message -----
From: "Jeff Kelly" <jkelly at bellatlantic.net>
To: <amsat-bb at amsat.org>
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