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



John,
I suggest you look at the back lobes of a Yagi. They vary depending on the
gain, and some max gain types do not have more than 7-10 dB F/B ratio,
especially if not pointed straight up. I would suggest a screen type
reflector to optomize the noise figure if you are using a Yagi type antenna
on 435 MHz or higher.

Art, KC6UQH
----- Original Message -----
From: "John B. Stephensen" <kd6ozh@verizon.net>
To: "Robert McGwier" <rwmcgwier@comcast.net>; <amsat-bb@amsat.org>
Sent: Tuesday, February 15, 2005 2:50 PM
Subject: Re: [amsat-bb] re: QRM 2m, question for sat builders


> If you have a yagi at 70 cm, you can take advantage of the decreased sky
> noise so the gain can be 7 dB less.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "Robert McGwier" <rwmcgwier@comcast.net>
> To: <amsat-bb@amsat.org>
> Sent: Tuesday, February 15, 2005 12:52 UTC
> Subject: RE: [amsat-bb] 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
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
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> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
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> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
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----
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