Hi Art,
this is a very good point. This is also one of the reasons why circular polarization was chosen for the commercial GPS system.
Best regards
Matthias
www.dd1us.de (including many soundfiles of AMSAT satellites)
-----Ursprüngliche Nachricht----- Von: Art McBride [mailto:kc6uqh@cox.net] Gesendet: Dienstag, 19. Mai 2009 07:50 An: 'Matthias Bopp'; amsat-bb@amsat.org Betreff: RE: [amsat-bb] Re: Gain VS Bandwidth at 2.4GHZ
One important feature of circular to circular antenna reception is the 30 dB of rejection of signals that are opposite polarity from ground and building reflections that will cause QSB on linear antennas used for reception. If you are 30 miles out to sea this is not a concern. Art, KC6UQH
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Matthias Bopp Sent: Sunday, May 17, 2009 7:38 AM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: Gain VS Bandwidth at 2.4GHZ
Hi Luc,
a linearly polarized antenna on a satellite means, that you will see different polarization at different times and different locations on Earth. Assume the satellites transmit vertical polarization but "tumbles" then the polarization you are receiving is always linear but can vary between vertical, diagonal, horizontal ... Therefore it is better if the satellite and the station on earth both use circular polarization. If this is not possible due to constraints on the satellite I think it is still better to have a circular polarized antenna at my station as the losses due to varying linear polarization will always be only 3dB and thus no strong fading due to polarization will accur. Please note that a tumbling satellite will most likely still generate strong fading as the antenna on the satellite will never have a perfect omni-directional behaviour.
Best regards
Matthias DD1US
www.dd1us.de
-----Ursprüngliche Nachricht----- Von: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] Im Auftrag von Luc Leblanc Gesendet: Sonntag, 17. Mai 2009 14:09 An: amsat-bb@amsat.org Betreff: [amsat-bb] Re: Gain VS Bandwidth at 2.4GHZ
On 16 May 2009 at 17:27, Roger Kolakowski wrote:
A part of my mystery is solved WiFi and WiMAX I am not a big fan of WiFi as i have some security concern but i discover that i don't have the best antenna for 2.4 and fiddling with it is not an option. A true 2.4 is in the mail to replace it and with 2 antennas now i will be able to install them to have vertical and horizontal polarisation and i will see if there is some improvement at 2.4ghz when switching between them. Nobody answer me back regarding the S band linear "not circular" AO-51 antenna but the fades are probably due to some antenna blocking than anything else. On the last S band session me and Clare VE3NPC noted that the fades does not happen at the same time on our respective QTH there is surely not some selective circular polarisation path?
This was probably just a typo; if so, pardon the reply...
I was mixing both...hi
Wi-Fi and Wi-Max are different things. An antenna designed for Wi-Max may not operate very well, as you describe, on 2.4 ghz. Wi-Fi's 802.11b/g is on 2.4 ghz (channel 1 is right on top of our allocation), so a properly designed Wi-Fi antenna could be good for 13cm Ham applications.
Enjoy the new toy,
Greg KO6TH
Some experimenting to come on the next S band session.
"-"
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
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_______________________________________________ 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
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