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RE: re: QRM 2m, question for sat builders



The two of your are agreeing and then agreeing to disagree.

FOR A YAGI, which is what Drew clearly has in mind,  the increased
path loss has to be made up with a much larger yagi on 70cm since
the increased path loss is 10 dB at (say) 1500 km slant range.  If
you used a dish on 2 meters (I don't recommend it ;-), the same
size dish will have the gain to overcome the increased path loss
at 70 cm.  The same capture area in a yagi at 70cm makes it much
larger.  Here is a path loss calculator.

http://gbppr.dyndns.org/PROJ/mil/ew/path_loss.main.cgi


Bob
N4HY


-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
Behalf Of Andrew Glasbrenner
Sent: Tuesday, February 15, 2005 11:06 AM
To: John B. Stephensen; amsat-bb@amsat.org
Subject: Re: [amsat-bb] re: QRM 2m, question for sat builders


>The path loss goes up with frequency but antenna gain goes up at the same
>rate for a constant size antenna. The pointing accuracy must be greater at
>higher frequencies but for the size antennas that amateurs use, this isn't
a
>limiting factor below 2 GHz.

To bring this back to the original point, the required use of directional,
gain antenna systems for receive is one of the factors that makes Mode J
more difficult to the beginner. Theoretical this and that aside, my
experience on the LEOs has shown that you can receive a 2m satellite
downlink from LEO on just about anythng better than a wet noodle, and the
same just can not be said for mode J.

73, Drew KO4MA
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