[amsat-bb] Re: more antenna discussions....
domenico.i8cvs at tin.it
Fri Mar 18 15:22:04 PDT 2011
Hi Jeff, KE7ACY
If the satellite transmit and receive in circular polarization RHCP or
LHCP then using horizontal polarization on the ground station is no
bad both for the uplink and downlink because you loose only 3 dB in
signal strenght but your linear antenna system is not complicated at
By the way if the satellite transmit in linear polarization then circular
polarization on the ground station is mandatory otherwise receiving
with linear polarization when the satellite and the ground polarizations
are opposite you loose at list 20 dB into the QSB
Since the most part of actual LEO satellites uses circular polarization
both receiving and transmitting then a horizontal polarization at the
ground station is fully satisfactory in uplink and downlink for satellite
work and as well for weak signal work particularly for a beginner
Obviously switching polarization between H-V-RHCP and LHCP for
the uplink and for the downlink is much better but it is a lot more
About the use or not of a elevation rotator with the actual LEO satellites
a fixed elevation of 20 degres is a good compromise because when the
satellite is overhead the attenuation decreases and the most part of the
time in wich a LEO satellite during a pass is above 45 degrees elevation
is very small.
----- Original Message -----
From: "Jeff Moore" <tnetcenter at gmail.com>
To: <amsat-bb at amsat.org>
Sent: Friday, March 18, 2011 9:13 PM
Subject: [amsat-bb] Re: more antenna discussions....
> Horizontally polarized beams will not work very well for satellite use.
> For maximum utility, I'd get crossed yagis set up to switch between
> horizontal,vertical, and circular polarization. Use the circular polarity
> to work the sats, horizontal polarity to do weak signal work, and vertical
> polarity to pull in those weak repeater and FM simplex signals.
> The az/el rotor set up will work best and give you maximum flexibility in
> your set up with the least impact on your above roof aesthetics.
> Jeff Moore -- KE7ACY
> On Fri, Mar 18, 2011 at 6:40 AM, zach hillerson <qstick333 at yahoo.com>
> > I'm still struggling to figure out the best antenna configuration for
> > me.
> > I was originally planning (and now own) to use a Gulf Alpha dual band
> > fixed at 15* elevation, but I am now having 2nd thoughts. Being limited
> > to 1 roof top tower it might be prudent to get as much use out of the
> > single mast as possible.
> > If I go with 2 horizontally polarized linear antennas on a cross boom
> > (1 ea. 2m and 440) could I use them for both satellites and weak signal
> > work? Is there a downside to proceeding this way?
> > One concern that I have is that the horizontal antennas seem to have a
> > somewhat limited frequency range, and I'm not sure of the impact. Also,
> > is it prudent to go with separate azimuth and elevation rotators to
> > allow for future expansion (6m etc...), although the separation required
> > between booms is height prohibitive with 6m?
> > Is anyone running a setup similar to this? Are you happy? Any
> > thoughts, opinions etc... would be appreciated,
> > Zach
> > N4ERZ
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