PUBLIC DOMAIN SOFTWARE ----   Author assumes no responsibility
                              for use of this product.  Values
                              contained herein were accurate
                              to the best of the author's
                              knowledge as of 03/23/88.

	This program may be freely distributed without payment of
	royalties or other license fees to the author.  The author
	encourages others to improve upon the program.  Please
	post all improvements on this bulletin board system so that
	the author may be informed of updates.


	SATFIX.BAS  written in IBM BASIC 3.10
	Author -  Bill Meeks, Jr.
		  1918 Tap Road
		Vidalia, GA  30474

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	This program calculates the antenna pointing angles for 
Satellite Earth Station Antennas.  You supply the longitude and
latitude coordinates for your antenna and the program computes
the "look angles".  In addition, it has the capability of
computing the downlink performance parameters of the earth
station.  The program contains Data Tables of the parameters
of several popular geostationary satellites for use in calculating
the expected quality of the received signal.  The user is prompted
for all input required for the calculations.


The table contains data for 17 C Band satellites (3.7-4.2 GHz) and
7 Ku Band satellites (12.2-12.7 GHz).  The last seven satellites
listed are the Ku Band birds.

Parameters supplied by the user are-

Antenna Diameter in Feet
Antenna Feed Assembly Efficiency (use 55 if you don't know)
Noise Temperature in Degrees Kelvin of the LNA (printed on LNA)
Desired Receive Frequency in GHz (usu. 3.96 for C, 12.5 for Ku)
The Threshold of your video demod (use 8 if you don't know)
The effective noise bandwidth of your receiver's IF Filter (generally given by
the manufacturer in the specs.  Average for home units is 26 MHz while
commercial units are usually 30 MHz or more.

Program responds with performance data showing antenna gain (dBi), antenna
beamwidth, received IF Carrier/Noise ratio and Fade Margin.

IF Carrier/Noise ratios less than 9 dB generally indicate marginal to poor
video reception.  The Fade Margin is the amount the Carrier/Noise ratio
exceeds the threshold of the demodulator.


Antenna efficiencies for Ku Band reception are generally very low, especially
for mesh dishes.  The efficiency can be as low as 35-40% on Ku.  Most decent C
Band dishes can produce around a 50-55% feedhorn efficiency rating.


If you obtain a fade margin of less than 1.5 dB you will probably see some
"sparklies" on most transponders, especially those with several audio
sub-carriers.  If the program predicts a high fade margin (>3 dB) for your
system and you have "sparklies" in your picture, then you are the owner of
either a badly aligned dish or a poor quality dish.  Sorry, but the program
does not know how to lie.

I run my system with a 12 feet diameter Prodelin fiberglass dish and have used
both a 100 degree and 60 degree LNA with a home built receiver based on boards
purchased from Scientific-Atlanta with a 32 MHZ IF bandwidth.  I get a perfect
picture on all the transponders on all the birds.  Only the Half-Transponder
NASA contract channel ever had a lousy picture.  The S/A boards have an IF
Carrier/Noise test voltage available on them and I have checked my actual C/N
ratio against the program's prediction and found the results within .25 dB of
each other.

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