[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Minimum Equipment for Digital Satellites



On Mon, 22 May 2000, A. Ferdinand Lubis wrote:

> I would like to ask you about possibility to work digital satellites
> (PACSAT) using this minimum setup (i.e. dual band HT + Egg beater
> antenna).

See http://web.usna.navy.mil/~bruninga/astars.html

My experience is that the "best" and simplest antenna for omni reception
of the digital satellites is a 20" vertical 2 meter whip over a 1 meter
or larger ground plane.  Such an antenna has almost 8 dBi gain at
elevations above 30 degrees.  This WILL receive data in that area of the
sky.  It will NOT receive these weak satellites on the horizon, but
neither will the egg beater.

The egg beater is an ideal cross polarized antenna for omni directional
satellite work.  There is no argument here at all.  BUT the problem is
that most of the current batch of amateur satellites just do not have a
strong enough signal to be heard low on the horizon where they are twice
as far away and 6 dB lower in signal.

Summary:
The eggbeater and other cross polarized OMNI antennas give excellent
hemispherical coverage down to the horizon.  But since most current 
digital downlinks are linear, mostly vertical, and too weak to be heard
on the horizon with ANY omni antenna, all these advantages are moot.

The 20" two meter whip, on the other hand, is a DUAL band antenna, is
vertical, and has an 8dB gain in high elevations on UHF.  It works very
well for the center 3rd of most passes above about 25 degrees.  The fact
that it wont hear on the horizon, and it wont hear horizontal components
during high faraday rotation on the horizon are not a real disadvantage,
because no other "omni" antenna can hear the weak signals down low on 
the horizon either.

> Please any suggestions welcome, especially about possibilies in using an
> HT+TNC and omnidirectional antenna as minimum requirement for digital
> birds.

I use a kenwood HT and a 20" whip over a one meter sheet metal ground
plane and can capture at least 3 to 5 minutes or more of data or voice
from all of the FM amateur satellites..

See the plot of the various antenna gains in the WEB page above (near the
bottom)..

de WB4APR, Bob

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home