Method for automatically positioning a satellite dish antenna to satellites in a geosynchronous belt

A TVRO satellite dish antenna system mounted on the roof of a parked vehicle automatically determines its location and bearing relative to two geosynchronous satellites and then uses this information to accurately calculate the azimuths and elevations of any other geosynchronous satellites. A magnetic compass generates a magnetic bearing signal for the system. An estimated latitude and longitude for the vehicle are provide by the user based on the approximate geographic location of the vehicle. The estimated positions for a first geosynchronous satellite and a second geosynchronous satellite relative to the satellite dish antenna are calculated from this information. The satellite dish antenna is moved to an initial search position corresponding to the estimated position of the first satellite and then moved in a search pattern until the receiver detects a signal peak for a selected channel. The actual azimuth and elevation of the first satellite are calculated based on the position of the satellite dish antenna upon detecting the signal peak. These steps are repeated for the second satellite. Revised bearing, latitude, and longitude coordinates for the satellite dish antenna are calculated based on the actual azimuths and elevations of the first and second satellites. Finally, the azimuth and elevation of any remaining geosynchronous satellite can be calculated based on the revised bearing, latitude, and longitude coordinates for the satellite dish antenna.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the field of television 
receive-only (TVRO) satellite dish antennas. More specifically, the 
present invention discloses a method for automatically positioning a 
satellite dish antenna mounted on a parked vehicle, such as a recreational 
vehicle, to locate geosynchronous satellites in the Clarke belt. 
2. Statement of the Problem. 
Over the past decade, TVRO antennas have grown substantially in popularity 
and are typically found in geographic areas of the United States where 
cable or broadcast television is not prevalent. Substantial programming 
exists on a number of satellites positioned in the Clarke belt, usually 
offering high quality programming through a paid descrambling system. Such 
commercially available programming from these satellites has found growing 
popularity among recreational vehicle (RV) users who would like to tap 
into this programming during their trips around the country in 
recreational vehicles. Initial satellite TVRO systems for recreational 
vehicles were simply comprised of a small TVRO dish antenna placed on the 
ground near the RV. The dish antenna was then manually adjusted with great 
care and time to locate and tune into an individual satellite. The tuning 
process would be repeated for tuning into another satellite. This approach 
was somewhat effective but resulted in considerable set-up time by the 
consumer and usually resulted in low quality signals in the television 
set. 
Some satellite dish antennas are designed to mount directly on the roof of 
the recreational vehicle. This eliminates the need for placement and 
storage of the satellite dish antenna such as described above. However, 
the alignment of the mounted satellite dish antenna to the satellite was 
still difficult due to the manual adjustments involved. An example of this 
type of conventionally available system is manufactured by RV Satellite 
Systems, 2356 South Sara Street, Fresno, Calif. 93706 under the trademark 
"BEST MADE." This antenna is designed to be raised and lowered from inside 
the RV and to be easily tuned into the satellite desired. The raising, 
lowering, and positioning of the dish antenna is done manually using a 
mechanical link between the inside and outside of the RV. 
A goal of TVRO satellite systems for use on RVs has been to fully automate 
the set-up and tuning of the dish antenna to all of the satellites. One 
conventionally available system providing semi-automatic set-up is 
manufactured by Elkhart Satellite Systems, 23663 U.S. Highway 33, Elkhart, 
Ind., 46517, which carries the trademark "MOTO-SAT." This system utilizes 
an electronic compass. 
Another conventional RV satellite dish antenna providing semi-automatic 
positioning is manufactured by The Dometic Corporation, 609 South Poplar 
Street, LaGrange, Ind., 46716. This system is manufactured under the 
trademark "A&E TRAVEL-SAT." The satellite dish antenna is mounted on the 
roof of the RV. When the RV is parked at a location such as a campsite, 
the RV is leveled and stabilized. The operator of the system uses a 
compass located at least six feet in front of the coach to ascertain the 
present compass heading of the coach (and therefore, of the antenna). The 
user turns on the receiver and the TV. The TV is set to a predetermined 
channel. The user then keys in the present compass heading into the system 
controller. The user refers to a "viewer's guide" to find the azimuth and 
elevation readings of the city nearest the campsite where the RV is 
parked. These coordinates correspond to the G1 satellite and are entered 
into the system controller by the user. The user presses the "aim" button 
on the system controller and the dish commences to move. As the dish 
moves, the user must closely watch the TV screen and, upon seeing a quick 
flash of an image across the screen, press the stop button on the 
controller. The user then presses "left" and "right" and "up" and "down" 
buttons to fine-tune the satellite dish into the image. After particular 
satellite is found, it must be identified so that the other satellites can 
be found. While this system provides an improvement over the earlier 
manual alignment approaches, it still involves substantial user 
interaction and time. It also requires the user's perception to watch for 
the images on the TV screen. The RETRIEVER.sup.TM system made by Vicor 
Industries, Inc. of Mission Viejo, Calif. 92690, follows an approach 
similar to the above. 
A wide variety of positioning systems have been used in the past for 
satellite dish antennas, including the following: 
______________________________________ 
Inventor Patent No. Issue Date 
______________________________________ 
Rodeffer et al. 
5,296,862 Mar. 22, 1994 
Horton et al. 5,077,560 Dec. 31, 1991 
Gorton et al. 5,077,561 Dec. 31, 1991 
Marshall et al. 
4,907,003 March 6, 1990 
Ma et al. 4,801,940 Jan. 31, 1989 
Ma et al. 4,785,302 Nov. 15, 1988 
Ma et al. 4,783,848 Nov. 8, 1988 
Shepard 4,602,259 July 22, 1986 
______________________________________ 
In the parent of the present application, Rodeffer et al. disclose a method 
for automatically positioning a satellite dish antenna on a parked vehicle 
for geosynchronous satellites. The satellite dish antenna is moved to an 
initial search position based on a bearing provided by a magnetic compass 
and approximate longitude and latitude values selected by the user using 
the approximate geographic location of vehicle. The satellite dish antenna 
is then moved in a search pattern to detect a signal peak for a selected 
audio subcarrier frequency in a selected channel of a target 
geosynchronous satellite. The frequency selected is not present in 
corresponding channels of other satellites near the target satellite. The 
azimuth and elevation positions of all remaining satellites can then be 
calculated. 
Horton et al. disclose an automatic drive for a TVRO antenna. The receiver 
calculates the position of each geosynchronous satellite. The antenna dish 
is initially pointed at each satellite and a peaking routine under 
operator control then maximizes signal strength for each satellite. These 
"peaked" positions are stored and subsequently used to repoint the antenna 
at each of the satellites during normal day-to-day operation. 
Gorton et al. disclose a computerized antenna mount system for continuously 
tracking a geosynchronous satellite that has an inclined orbit with 
respect to the equator. The antenna mount automatically adjusts the 
declination angle of the ground station satellite antenna as a function of 
time after iteratively compiling the declination angle history from one 
complete orbit of a satellite. 
Marshall et al. disclose a satellite receiver and acquisition system that 
uses an antenna search routine to maximize signal strength during setup. 
U.S. Pat. No. 4,801,940 to Ma et al. discloses another example of a 
satellite-seeking system for a TVRO antenna. 
U.S. Pat. No. 4,785,302 to Ma et al. discloses an automatic polarization 
control system for TVRO receivers. 
U.S. Pat. No. 4,783,848 to Ma et al. discloses a TVRO receiver system for 
automatically locating audio signals among various audio subcarriers 
received from different transponders without the need for manual scanning. 
Shepard discloses another example of a polar mount for a parabolic 
satellite-tracking antenna. 
Solution to the Problem 
None of the prior art references uncovered in the search show a TVRO 
satellite dish antenna system mounted on the roof of a parked vehicle that 
automatically determines its location and bearing relative to two 
geosynchronous satellites and uses this information to accurately 
calculate the azimuth and elevation position of any other geosynchronous 
satellite. The use of two geosynchronous satellites provides greater 
assurance that the location and bearing of the vehicle have been 
accurately determined. If only one geosynchronous satellite is used, all 
errors in the estimated location and bearing of the vehicle are lumped 
into one correction factor that is then used in calculating the relative 
angles for all other satellites. However, this single correction factor 
may be inaccurate for other satellites. For example, a combination of 
errors in the estimated location, bearing, and leveling of the vehicle 
might offset one another if only one geosynchronous satellite is used, 
thereby leading to the false indication that the system has been properly 
set up. 
SUMMARY OF THE INVENTION 
This invention provides a TVRO satellite dish antenna system mounted on the 
roof of a parked vehicle that automatically determines its location and 
bearing relative to two geosynchronous satellites and uses this 
information to accurately calculate the azimuths and elevations of any 
other geosynchronous satellite. A magnetic compass generates a magnetic 
bearing signal for the system. An estimated latitude and longitude for the 
vehicle are provide by the user based on the approximate geographic 
location of the vehicle. The estimated position for a first geosynchronous 
satellite relative to the satellite dish antenna is calculated from this 
information. The satellite dish antenna is moved to an initial search 
position corresponding to the estimated position of the first satellite 
and then moved in a search pattern until the receiver detects a signal 
peak for a selected channel. The actual azimuth and elevation of the first 
satellite are calculated based on the position of the satellite dish 
antenna upon detecting the signal peak. These steps are repeated for a 
second geosynchronous satellite. Revised bearing, latitude, and longitude 
coordinates for the satellite dish antenna are calculated based on the 
actual azimuths and elevations of the first and second satellites. 
Finally, the azimuth and elevation of any remaining geosynchronous 
satellite can be calculated based on the revised bearing, latitude, and 
longitude coordinates for the satellite dish antenna. 
A primary object of the present invention is to provide a TVRO dish antenna 
system for use on vehicles that can be automatically positioned relative 
to geosynchronous satellites without requiring the user to provide 
detailed information concerning the bearing, longitude, and latitude of 
the vehicle. 
Another object of the present invention is to provide a TVRO dish antenna 
system for use on vehicles that can be quickly and easily positioned 
relative to geosynchronous satellites with a minimum of involvement by the 
user. 
These and other advantages, features, and objects of the present invention 
will be more readily understood in view of the following detailed 
description and the drawings.

DETAILED DESCRIPTION OF THE INVENTION 
1. Overview 
In FIG. 1, the satellite dish antenna 10 of the present invention is 
mounted to the roof 20 of a recreational vehicle 30 that is parked at a 
campsite 40. The vehicle 30 is oriented in a direction that is displaced 
from true north by an angular direction .THETA. indicated by arrows 50. 
The antenna 10 is connected to a receiver 60 that in turn is connected to 
a television 70. While the present invention finds application for use on 
any vehicle, in the preferred embodiment the vehicle is a recreational 
vehicle (RV), and the following disclosure will only refer to use on an 
RV. However, the scope of the invention is not to be limited to use on an 
RV. In fact, the present invention could be mounted on a building, but the 
invention is most suitably useful on vehicles that move from location to 
location. Hence, the term "vehicle" is used to mean any "carrier" that can 
move from location to location so as to have different longitudes and 
latitudes. The term "object" would include a carrier and a fixed support 
such as a building. 
In operation, the satellite dish antenna 10 is folded in a downward 
position while the RV 30 is moving to the campsite 40. When the RV 30 is 
parked at the campsite 40, the user activates the receiver 60 and the dish 
antenna 10 unfolds. The user inputs the city location into the receiver 60 
based on a menu or list of cities appearing on the TV 70. The inputting of 
the city location by the user provides the latitude and longitude to the 
receiver 60. A magnetic compass 80 mounted on the mount of the satellite 
dish antenna 10 is automatically read by the receiver 60 to provide 
angular deviation data .THETA. from true north (i.e., termed a "direction 
signal"). Based on the manually entered latitude and longitude values and 
the generated electronic compass reading 80, the satellite dish antenna 10 
is automatically moved in the azimuth and elevation directions to the 
general direction of a target satellite 90 (i.e., the initial search 
position). 
The satellite dish antenna 10 under control of the receiver 60 changes 
elevation E under control of an elevation motor 100 and changes azimuth 
direction A under control of an azimuth motor 110. This type of mount is 
conventional and is well known in the industry as an azimuth/elevation 
(AZ-EL) type of mount. With the satellite dish antenna in the initial 
search position, a predetermined rough-tune search pattern is first used 
by receiver 60 to ascertain the presence of a first peak signal from a 
selected audio subcarrier frequency (i.e., 5.14 MHz) appearing in a 
selected channel (i.e., Ch. 6) of the target satellite 90 (i.e., ANIK-E2). 
If a first peak signal is found in the rough-tune search, a finetune 
search pattern is then used by receiver 60 to precisely locate a second 
peak signal for the selected audio subcarrier. The satellite dish antenna 
10 is now properly positioned along a boresight 120 to receive signals 
from the target satellite 90. At this time, the target satellite 90 is 
identified and the locations (i.e., azimuth and elevation positions) of 
all of the other satellites in the Clarke belt 130 can be precisely 
located by the receiver 60. 
The user interacts with the system only to turn the receiver 60 on and to 
enter the location through a menu select. Otherwise, the receiver 60 of 
the present invention, based on the entered location and the compass 
reading, automatically (1) unfolds the antenna to an approximate boresight 
for a selected satellite 90 based on the location and compass reading; (2) 
performs the rough-tune search that roughly locates the boresight of the 
antenna to a selected audio subcarrier signal; and (3) performs the 
fine-tune search that precisely locates the boresight 120 of the antenna 
10 to receive the audio signal. 
The system of the present invention is designed to be extremely 
"user-friendly" in locating satellites in the geosynchronous Clarke belt. 
As discussed next, the user simply parks the RV and enters the approximate 
latitude and longitude. The system will automatically find a preprogrammed 
target satellite. Once the target satellite has been found, all the other 
satellite locations are automatically calculated. 
2. Receiver 60 
In addition to having the standard electronic circuitry for TVRO tuning and 
reception including the descrambling circuitry, the receiver 60 of the 
present invention, as shown in FIG. 2, includes a microprocessor 200 and 
associated digital electronics described in the following. 
The receiver 60 is interconnected to the television set 70 over lines 62 so 
as to display graphics on the screen 72 of the television. The receiver 60 
also receives transmitted signals 64 from a remote control 210. The remote 
control 210, under the preferred embodiment, is an infrared (IR) remote 
control (pulse-position modulation), although it is to be expressly 
understood that this input device could comprise buttons on the TV 70, on 
the receiver 60, or on a separate electronics package; in which event, the 
link 64 would most likely be electrical wires. The receiver 60 is also 
interconnected over lines 66 to the elevation motor 100 and to the azimuth 
motor 110, both of which are mechanically interconnected to the TVRO dish 
10 over mechanical links 102 and 112, respectively. The receiver 60 is 
also connected over lines 68 to an electronic compass 80 that is 
mechanically connected 82 to the dish antenna 10. The compass 80 is a 
magnetoflux compass and is hard mounted to the AZ-EL mount so that the 
compass accurately measures the magnetic direction of the mount. The 
compass 80 measures the approximate heading or direction of the mount (or 
RV). The antenna 10 is a 4.5 foot parabolic mesh antenna. 
In general operation, the receiver 60 provides graphic communications in 
the form of screen menus to the monitor 72 of TV 70 over lines 62. The 
user of the present invention uses the remote 210 or other comparable 
input device to deliver signals over communication pathway 64 to the 
receiver 60 in response to queries in the menus on TV 70. For example, a 
directory of cities could be displayed in the monitor of TV 70 and the 
user of the present invention could use the remote 210 to select a given 
city. Based on that city's selection, the receiver 60 (in response to a 
reading from the electronic compass 80 delivered over lines 68) would 
issue motor control signals over lines 66 to the azimuth motor 110 and to 
the elevation motor 100, which would then mechanically position dish 10 in 
the general direction of the target satellite 90 in the Clarke belt 130. 
The receiver 60 as shown in FIG. 2 uses a central bus 202 that 
conventionally comprises address, data, and control busses. The 
microprocessor 200 is interconnected to bus 202. In the present invention, 
the microprocessor 200 is a 16-bit microprocessor such as the Model 68008 
manufactured by Motorola. A clock 203 is used to provide clock signals to 
the microprocessor 200. In the preferred embodiment the conventional clock 
is a 5.365 MHz clock. 
Also connected to the bus 202 is a static random access memory (SRAM) 204. 
A lithium battery 205 is used to provide power backup to the SRAM 204. The 
SRAM 204 holds all channel information for each of the 36 channels and for 
up to 36 satellites (1296 channels total). The SRAM 204 also holds all 
satellite position information (such as label, azimuth position, elevation 
position, and orbital position). The channel and position information is 
loaded into the SRAM 204 at manufacture. The SRAM 204 also holds the 
variable information as will be explained later. In the preferred 
embodiment, the conventional SRAM 204 is a 32K by 16 bit memory. 
Also connected to bus 202 is an electronic programmable read-only memory 
(EPROM) 206 that contains the software necessary to operate the system of 
the present invention. The EPROM 206 is preferably 128K bytes in size. A 
real time clock 207 is conventionally interconnected to a bus 202. A 
conventional video display processor (VDP) 208 is interconnected to the 
bus 202 and a conventional video dynamic random access memory (DRAM) 209 
is also interconnected. The output of the DRAM 209 is delivered over lines 
62 to a conventional on-screen display (OSD) video output. The VDP 208 
works in conjunction with the microprocessor 200 to generate full-screen 
menus that the user sees when operating the receiver 60. The 
microprocessor 200 writes information into the DRAM 209, and the VDP 208 
processes the contents of this memory and converts it to video. It is with 
these menus, as illustrated later, working in conjunction with the IR 
remote 210 that the user operates the receiver 60. Preferably there are no 
front panel controls or displays on the receiver 60 itself. 
Also connected to bus 202 is the infrared decode circuit 211, which is 
conventionally interconnected to an IR sensor 212. Both components are 
conventionally available. A latch 213 is connected to the bus 202; in the 
preferred embodiment this is an 8 bit latch. A conventional eight bit 
analog/digital circuit (ADC) 214 is interconnected over lines 68 with the 
electronic compass 80. 
The operation of the hardware configuration set forth in FIG. 2 will be 
more fully explained in the following. Generally speaking, the 
microprocessor 200 based on programming appearing in EPROM 206 activates 
the VDP 208 to display in the TV 70 predetermined screen menus. The IR 
decode circuit 211 receives operator commands from the remote device 210 
so as to cause the microprocessor 200 to follow the correct operating 
sequence desired by the user. The microprocessor 200, by loading proper 
data in latch 213, can precisely cause the azimuth motor 110 to move 
incrementally in the azimuth direction and can cause the elevation motor 
100 to move incrementally in the elevation direction. The microprocessor 
200 can obtain the precise heading of the dish 10 by reading the ADC 
circuit 214, which carries the compass reading 80. 
In FIG. 2, the details of the conventional receiver operation are not set 
forth. One aspect of the present invention is the ability to tune into an 
audio subcarrier during a rough and fine tune search as will be discussed 
later. The circuitry for receiving and tuning is conventional; however, 
the conventional audio subcarrier demodulator 261 has been modified to 
deliver the analog signal of the subcarrier over line 262 into the ADC 214 
so that the corresponding digital value of the signal can be used by the 
microprocessor 200 in the search process. 
The receiver 60 circuitry set forth in FIG. 2 is a preferred embodiment. It 
is to be expressly understood that variations to this circuitry could be 
made by one skilled in the art under the teachings of the present 
invention. 
3. System Operation 
In FIG. 3, the overall system operation is shown. The operator turns on the 
system at stage 300. That is, the user turns on the receiver 60 and the 
television 70. The system becomes initialized in stage 310. 
In stage 310, the satellite dish antenna 10 unfolds from the traveling 
position and orients to an initial position. This initial position would 
be, for example, the last position in which the antenna 10 was oriented by 
the user in order to receive a picture from the antenna 10 (i.e., the 
night before at a different campsite). If the RV 30 had not moved to a new 
location and was still in the same position, the antenna 10 would simply 
position to the last viewed satellite. In stage 320, therefore, if the 
dish antenna 10 is already tuned to a satellite 90 and a picture is 
received, stage 330 is entered and the tuning process is complete. The 
user will conventionally view the TV 70 and move from satellite to 
satellite and from transponder to transponder in a conventional fashion. 
However, if the dish antenna 10 is not tuned to a transponder, stage 340 
is entered and the target menu is displayed. In FIG. 4, an example of a 
target menu is shown. 
In FIG. 4, the target menu 400 is displayed on TV 70. As shown in FIG. 4, a 
city field 410, a latitude field 420, a longitude field 430, a compass 
heading 450, and several search characteristics fields 460 are provided. 
The user can select items 1 through 9, and when an item is selected, 
information may be selectively entered. For example, if the RV 30 was in 
Burlington, Iowa, the night before and now is in or near Sioux City, Iowa, 
the city item field 410 would be selected so as to modify this field 410. 
The user selects item "1". 
In FIG. 5, the city menu 500 is now displayed. The user will select Sioux 
City 510, which will then be loaded by the microprocessor 200 into the 
target menu 400 with Sioux City's coordinates of longitude and latitude. 
This provides approximate latitude and longitude values to the receiver 
60. This occurs in stage 350 as shown in FIG. 3. 
Returning to FIG. 4, the system has already read the compass reading from 
the compass 80 and has entered in the compass heading or direction in 
field 450. Hence, the operator would select item 9"Search for Satellite" 
and stage 370 is entered. 
It is to be understood that in stage 340, the operator could have referred 
to a map or other information to obtain a more precise longitude and 
latitude (such as a U.S. Geophysical map for the campground area). In this 
case the user would have selected items 2 and 3 in FIG. 4 to manually 
enter the longitude and latitude in stage 340. It is also to be expressly 
understood that the operator could override the compass by entering step 
4. In this case, the operator could turn the compass off and manually read 
a compass so as to enter the heading in step 5. However, in normal 
operation, all that is required is for the user to select the nearest 
city, which in the above example is Sioux City. The city information is 
stored in the SRAM 204. The city list is a list of geographic locations 
that the system might be moved to, and each entry in this list contains a 
name, state code, corresponding location (latitude/longitude), and the 
magnetic declination associated with the location. In addition, the target 
menu 340 allows the operator to change the search characteristics: the 
initial predetermined satellite, the search channel, and the search 
frequency. This will be discussed subsequently. 
Returning to FIG. 3, with the longitude and latitude for Sioux City entered 
in stage 360, the system automatically moves the antenna dish 10 searching 
for the predetermined satellite, for example, ANIK-E2. This searching 
process involves rough and fine tune searches in stage 370. If the 
predetermined satellite is not found, stage 380 is entered and a message 
is generated on the screen 72 that the target satellite could not be 
found, upon which stage 340 is entered and the process repeats. However, 
in the event the target satellite (ANIK-E2) is found, stage 390 is entered 
and the picture is displayed. 
The operation of the system set forth in FIG. 3 requires only minimal 
operator input. In the typical case, simply selecting the nearest city 
from the city menu 500 in stage 350 is all that is required. From that 
point on, the system is fully automatic in aligning the satellite dish 10 
to the target satellite 90. When the antenna 10 is aligned with the target 
satellite 90, the positions of the other satellites in the Clarke belt can 
be automatically calculated. 
The menus shown in FIGS. 4 and 5 are those of the preferred embodiment. It 
is to be expressly understood that variations could be made thereto. For 
example, a digitized map could be shown as a menu and the location could 
be suitably chosen using a mouse control or the like. 
In summary, the automated method of the present invention (1) generates a 
magnetic direction signal from a magnetic compass mounted on the satellite 
dish antenna, (2) stores a plurality of latitude and longitude coordinates 
correlated to a plurality of geographical locations, (3) displays in the 
TV 70 the geographic locations so that the user can select one, and (4) 
determines an initial search position based on the magnetic direction 
signal and the selected latitude and longitude coordinate. 
4. Audio Subcarrier Search 
An important feature of the present invention is the ability of the system 
to search for a specific audio subcarrier located in the target satellite. 
FIG. 6 shows a list of potential target satellites that could constitute 
the target satellite of the initial search. For each potential target 
satellite, a particular or predetermined channel has been selected and for 
that channel a unique subcarrier audio frequency is chosen. In scanning 
the list of FIG. 6, it is noted that each audio subcarrier frequency is 
uniquely different from the adjacent satellite's selected subcarrier 
frequency. For example, for ANIK-E2, channel 6 has a selected audio 
frequency of 5410 KHz, which is different from the adjacent GALAXY 
satellite channel 13 subcarrier frequency of 5760 KHz. Under the teachings 
of the present invention and in the preferred embodiment, channel 6 of 
ANIK-E2 having a subcarrier frequency of 5410 KHz represents a unique 
searching audio frequency of strong signal strength. The goal is to avoid 
using frequencies that are common to the same channels of adjacent 
satellites, such as 6800 KHz. 
As shown in FIG. 6, menu 600 is displayed on TV 70 and the user at any time 
can select another satellite as the target satellite for the initial 
search by simply selecting a field such as 610. 
Under the teachings of the present invention, the selected audio subcarrier 
is unique. That is, the frequency of the selected audio subcarrier is not 
present in the corresponding channel of any satellites near the target 
satellite. 
In the preferred embodiment, the search menu of FIG. 6 is the list that 
contains the information necessary for the system to perform the search 
for the target satellite by looking for a predetermined subcarrier audio 
frequency at a predetermined channel or transponder location. This search 
characteristic list is stored in the SRAM 204. Use of the system of the 
present invention is as simple as entering the approximate latitude and 
longitude. Once these have been established, the search routine of FIG. 3 
finds the target satellite. Upon locating the target satellite, the system 
accurately locates the positions of all the remaining satellites in the 
Clarke belt. In typical operating time, the operation of FIG. 3 is 
accomplished in as few as two or three minutes. The present invention 
greatly simplifies the process of locating each satellite and minimizes 
the knowledge requirements of the user who, under prior approaches, had to 
watch the television for a passing image. 
Under the teachings of the present invention, the target satellite can be 
located accurately by selecting a unique subcarrier audio frequency. For 
example, all satellites have a 6.8 MHz audio subcarrier frequency. The 
selection of this audio frequency would be inappropriate since upon its 
detection, the actual identity of the satellite would not be known. 
However, selecting 5.41 MHz in channel 6 of the satellite ANIK-E2 would be 
appropriate, since no other satellite adjacent to ANIK-E2 has a 5.41 MHz 
audio subcarrier frequency. Hence, this is an important part of the 
present invention in that the targeted audio subcarrier frequency is 
uniquely different from the audio subcarrier frequencies of the adjacent 
satellites. This is also to be contrasted with most conventional prior art 
approaches that look for video frequencies. All video center frequencies 
look alike from satellite to satellite and therefore, it is impossible to 
determine which satellite has been detected and to which satellite the 
system is tuned. Hence, these prior art systems require that the operator 
visually identify the satellite by watching the received signal. This 
requirement is obviated under the teachings of the present invention. 
5. Searching for the Target Satellite 
In FIG. 7, the method of searching for the target satellite implemented by 
the receiver 60 in cooperation with the dish antenna 10 is shown. FIG. 7 
sets forth the detailed steps for the search stage 370 of FIG. 3. Stage 
370 is entered at 700. As shown in FIG. 8, the RV 30 may be oriented with 
the front 32 of the RV 30 pointed in the northern hemisphere 800. If the 
front 32 of the RV 30 is pointed in the southern hemisphere 810, then the 
reading from the electronic compass 80 delivered over line 68 into the 
receiver 60 causes the microprocessor 200 to adjust the following 
calculations by 180.degree.. If the RV 30 is pointed in the northern 
hemisphere 800, then stage 730 is entered. If the RV 30 is pointed in the 
southern hemisphere, then stage 730 is entered with the calculation 
adjusted by 180.degree.. 
In stage 730, the microprocessor 200 calculates the initial search position 
of the target satellite 90. 
6. Calculation of Target Satellite Initial Search Position 
The satellite dish antenna 10 is first moved to an approximate position of 
the target satellite based on the latitude, longitude, and magnetic 
declination corresponding to the city nearest to the location of the 
campsite (or, as manually entered by the operator). This approximate 
position is calculated as follows. 
In FIGS. 9 and 10, the conventional TVRO-satellite geometry is set forth. 
In FIG. 9, the earth 900 is stylized having the North Pole located at 910 
and the South Pole located at 920. The target satellite 90 is located in 
the Clarke belt, which is directly above the equator 930. The center point 
of the earth is at CP. Shaded area 920 represents a portion of the surface 
of the earth 900. Line segment AC having a length "b" is along the equator 
930. Line segment BC having a length "a" is along a circular arc 940 that 
travels through point B, which is the location of the satellite dish 
antenna 10, to a corresponding latitude point C on the equator 930. Line 
segment AB having a length "c" is the distance between the satellite dish 
antenna 10 at point B and the satellite 90 at subpoint A on the equator 
930. The target satellite 90 has an altitude H above the surface 900, 
which is the distance from A to the target satellite 90. Of course, point 
A is located a distance R from the center CP of the earth 900. Hence, the 
distance S from the target satellite 90 to the TVRO satellite dish 10 at 
point B is the slant range. The azimuth angle AZ is the angle between line 
S and the center line 940. 
In FIG. 10, a different view of the geometry of FIG. 9 is presented. Here, 
the elevation angle E is shown as the angle between the tangent line 1000 
with the earth 900 at point B and the slant range S. 
Based on the TVRO satellite geometry set forth in FIGS. 9 and 10, which is 
conventional, the microprocessor 200 of the present invention is able in 
stage 730 to calculate the approximate position of the target satellite 
90. 
In the calculations set forth later, the following values are utilized: 
B=location of the recreational vehicle or ground station (GS) 
a=latitude of point B (positive in a northern hemisphere) 
c=great circle arc from point B to point A 
g=longitude of point B (east is positive) 
f=longitude of target satellite 90 (east is positive) 
b=g-f 
AZ=azimuth angle 
E=elevation angle 
S=slant range 
H=altitude of satellite 
R=radius of earth 
It is to be understood that the values of f, H, and R are all fixed for the 
target satellite and are stored in the EPROM 206 of the receiver 60. 
7. Calculation of Approximate Elevation Angle 
The calculation of the approximate elevation angle E is: 
##EQU1## 
where: These calculations provide the true elevation angle E. This must be 
transformed to the motor-driven mount for moving the antenna 10 in the 
elevation direction. The following calculations are based on the antenna 
mount set forth in the above-identified related invention. It is to be 
expressly understood that the teachings of the present invention are not 
limited to the precise mounting design of the related invention and that 
any suitable mechanical mount could be similarly transformed so as to be 
used under the teachings of the present invention. Hence, the following 
discussion of FIGS. 11a through 11c is for the preferred embodiment and is 
not meant to limit the teachings of the present invention in any fashion. 
The mount of the related invention has three pivot points, P1, P2, and P3. 
FIG. 11a shows the antenna 10 in the stowed position, FIG. 11b shows the 
antenna 10 unfolding, and FIG. 11c shows the antenna 10 tuned to the 
target satellite 90. 
In FIG. 11a, pivot point P3 is fixed to the roof 20 of the RV 30. It is 
connected to pivot point P2 by means of a member 1110 having a length of 
R1. Pivot point P1 moves along line 1100 on the roof 20 a plus or minus 
distance. Line 1100 represents the direction of actual travel, hence, 
point P1 can move in plus or minus incremental steps along line 1100. 
Pivot point P1 is connected to pivot point P2 through a member 1120 having 
a length of R2. Point P3 is separated from line 1100 by a distance d. 
Member 1120 extends beyond point P2 and at 1130 undergoes an angle B with 
respect to member 1120 and forms a new member 1140 that connects to the 
antenna 10. Line 1150 is the antenna boresight of antenna 10. Line 1160 is 
the horizon line. As shown in FIG. 11a, elevation angle E is the angular 
relationship between the antenna boresight 1150 and the horizon 1160. 
In the preferred embodiment, the following are the values for the mount of 
the related invention: 
E=-90.degree..ltoreq.E.ltoreq.90.degree. 
R1=5.526" 
R2=5.066" 
d=3.00" 
B=-9.227.degree. 
-1.000".ltoreq.x.ltoreq.11.000" 
As mentioned, FIG. 11a represents the antenna 10 in the stowed position 
with the boresight 1150 pointed at the roof 20. 
In FIG. 11b, the receiver 60 activates the elevation motor 100 to move 
point P1 in the direction of arrow 1170. This causes point P2 to move 
upward in the direction of arrow 1172. At this point, point P1 is 
incrementally moving in the plus direction. The boresight 1150 of the 
antenna 10 is still below the horizon 1160. An important feature of the 
present invention pertains to the initial raising of the antenna 10 in the 
elevation direction. The software in the receiver 60 requires the antenna 
10 to be lifted upward a predetermined height, Z, as shown in FIG. 1lb, 
before any rotation in the azimuth direction takes place. This is 
necessary to prevent the antenna 10 from hitting nearby objects (such as 
air conditioning, vent pipes, etc.) on the roof 20 of the vehicle 30. 
In FIG. 11c, the antenna 10 is pointed in the proper elevation direction of 
the target satellite 90. Based on the elevation transform model of FIG. 
11, the value of x of can be calculated as follows: 
##EQU2## 
The value of x is the distance of movement required by actuator motor 100 
to achieve the desired elevation angle E. This value would be the actual 
value required assuming the actuator actually coincided with line 100. 
However, in the preferred embodiment, the actuator is offset from line 1100 
as shown in FIG. 12. In FIG. 12, the actuator travel line 100 of FIG. 11 
is shown. Point P1 slides along that line in the direction of arrow 1170. 
In FIG. 12 the following dimensions are based upon the mount of the 
related invention: 
z=distance from line 1100 to pivot point P4=4.500" 
y=distance from pivot point P4 to the center line of the actuator 
1200=1.125" 
D=the stowed dimension=27.785" 
x'=the distance that the actuator moves 
I=the length from line z to the ORIGIN=26.785" 
x.sub.min =the minimum.times.distance=-1.000" 
D=1-x 
C.sub.el =(x'.sub.max -x')pt=number of counts for elevation 
t=lead screw pitch for the actuator in turns per inch (TPI) 
p=pulse edges per revolution 
x'.sub.max =maximum length of actuator=28.125" 
The values of t and p for a particular actuator 1200 are constant. The 
pulse edges per revolution p are based on an optical interrupt approach 
detecting the edges per revolution. The geometric relationship in FIG. 12 
simply provides the offset relation of x to x'. Hence, x'is related to x: 
##EQU3## 
Hence, the actual number of counts necessary to achieve a certain amount 
of elevation angle E for a particular actuator has been calculated. The 
computer upon performing the above calculations commands the elevation 
motor 100 through the latch 213 to activate the actuator by a certain 
number of counts C.sub.el over the mechanical interconnection 102, as 
shown in FIG. 12. The antenna 10 is thus moved to the elevation initial 
search position. 
8. Determining Azimuth Increments 
Returning to FIGS. 9 and 10, the azimuth calculations are determined as 
follows: 
##EQU4## 
In the preferred embodiment of FIG. 13, the worm gear 1300 engages a ring 
gear 1310. The antenna dish 10 is mounted on the ring gear 1310 by member 
1320. Hence, the azimuth (AZ) can be adjusted based on the following 
formula: 
##EQU5## 
The following values are used in the above formula: 
N=number of teeth on the ring gear 1310 
P1=pulse edges per revolution of the worm gear 1300 
.theta.=compass setting: -90.degree..ltoreq.0.ltoreq.90.degree., 
-90.degree. is east, +90.degree. is west 
C.sub.az =the counts necessary for the azimuth motor 110 to rotate the worm 
gear 1300 through the mechanical linkage 112 to achieve the desired 
azimuth of the target satellite 90. 
Again, the precise embodiment shown in FIG. 13 corresponds to the mount set 
forth in the related invention. It is to be expressly understood that any 
other mechanical apparatus adjusting the antenna 10 in the azimuth 
direction could be likewise mathematically transformed under the teachings 
of the present invention and that the present invention is not limited to 
the precise disclosure of FIG. 13. 
Returning back to FIG. 7, at this point stage 730 is completed. The antenna 
10 at this time is approximately positioned, under control of receiver 60, 
to the target satellite 90. 
Stage 740 is then entered. In stage 740, the receiver 60 is tuned for a 
selected audio frequency of the target satellite 90, which in the target 
menu 400 of FIG. 4 is ANIK-E2, channel 6, audio subcarrier frequency 5.41 
MHz. 
In stage 750 the antenna 10 is now physically moved to the calculated 
azimuth initial search position of stage 730. Once the antenna 10 is in 
the initial search position, stage 760 is entered and the search now 
commences for the selected audio frequency in the selected channel of the 
target satellite 90. 
9. Rough-Tune Search Pattern 
FIG. 15 illustrates the steps taken by the present invention to conduct the 
rough-tune for the selected audio frequency of the selected channel. The 
execute search stage 760 is entered at the start 1500. At stage 1510, the 
initial scan step of I is set to 1. Stage 1514 is then entered. At this 
point, reference to FIG. 14 is important. In FIG. 14, the antenna 10 has 
its antenna boresighted at an initial calculated position that in FIG. 14 
is referenced as J. The value of J was calculated in stage 730 and is the 
position of the azimuth and elevation motors. 
The rectangular spiral search pattern shown in FIG. 14 for the rough-tune 
incrementally moves to the right in the u direction, then incrementally 
moves downward in the perpendicular v direction, then to the left in the 
2u direction, then upward in the 2v direction, etc. This provides an 
ever-expanding spiral search pattern. The rough-tune search pattern moves 
the antenna 10 in a first linear direction, which could be either the 
azimuth or elevation direction, a given amount, u. The antenna 10 is then 
moved in a second linear direction that is perpendicular to the first 
linear direction a second given amount, v. In the preferred embodiment, 
the antenna 10 is then moved in the direction opposite the first linear 
direction by an amount equal to twice the first given amount or 2u. It is 
to be understood that "u" could be increased by any suitable constant 
value, which in FIG. 14 is by the amount of "u." The antenna is then moved 
in the direction opposite the second linear direction by an amount equal 
to twice the second given amount or 2v. It is to be understood that "v" 
could be increased by any suitable constant value, which in FIG. 14 is by 
the amount of "v." 
Returning now to stage 1514 of FIG. 15, the boresight of the antenna 10 is 
initially moved from point J along the u direction for a first scan step 
of I=1. During this movement, a predetermined number of readings such as 
twelve are taken. During the u movement, in stage 1518, these twelve 
discrete readings are taken by the receiver 60. It is important to 
remember that the receiver 60 is tuned in to receive a precise subcarrier 
audio frequency. The twelve readings are taken at evenly spaced intervals 
during the "u" movement. In stage 1520 the readings are stored as to the 
signal strength detected. The processor 200 stores this information in the 
SRAM 204. Stage 1524 is then entered to ascertain whether the 12 readings 
have been taken. If twelve readings have been taken, then stage 1528 is 
entered. The antenna 10 is then stopped at point 1400. Stage 1530 is 
entered and the twelve readings taken during stage 1518 are processed. 
FIG. 16 sets forth the details of the process data step 1530. This stage is 
entered in the start 1600, and the first stage 1604 utilizes a statistical 
program to discard obvious flawed data. In the preferred embodiment, the 
ADC 214 of FIG. 2 may not operate fast enough thereby generating "zero" 
readings. This data, when sampled, is obviously flawed and is discarded. 
Stage 1608 is then entered, which computes the average of the remaining 
valid data. FIG. 20 sets forth an example of data illustrating a satellite 
that will be found, whereas FIGS. 21(a)-(c) set forth an example of data 
illustrating a situation in which a satellite will not be found. In FIGS. 
20(a) and 21(a), the original data without the flawed data is shown. The 
horizontal axis sets forth the reading, i, and the vertical axis sets 
forth the signal strength. In stage 1608, the average is calculated, which 
for FIG. 20(a) is 42.67, and for FIG. 21(a) is 40.6. In stage 1614, the 
signal is converted to a "signal" or "no signal" value. This is 
represented in FIGS. 20(b) and 21(b). The signal data is recorded as a 
"signal" or "no signal" (i.e., either a 0 or a 1) based on whether the 
individual signal data is above the determined average. In the preferred 
embodiment, a level of "3.0" is utilized so that the limit is 3.0 above 
the average. In the case of FIG. 20, the average is 42.667. Adding 3 to 
this results in a limit of 45.67. Hence, all data points above 45.667 
become a "1" or a signal and all values below the limit become a "0" or no 
signal as shown in FIG. 20(b). The same is true of FIG. 21(b). 
Stage 1620 is then entered and the data is smoothed. This is shown in FIGS. 
20(c) and 21(c). The data that is smoothed is a collection of 1's and 0's 
as previously discussed. The weight of each data point upon its neighbors 
is determined by its distance from its neighbors. Points that are further 
away than the range are considered to have no effect. 
Hence, in FIG. 20(c) and 21(c), the smooth data appears for each example. 
In FIG. 20(c), the peak is found at 2000. The threshold of 19 is also 
shown in FIG. 20(c). The peak 2000 represents the position of a found 
satellite. In FIG. 21(c), the threshold is also 19 and two peaks are 
found, indicating that the satellite cannot be located. 
Stage 1630 is then entered. A determination is made as to whether the 
smoothed maximum peak is large enough. If not, stage 1640 is entered and 
the process data stage 1530 is ended. On the other hand, if the smooth 
maximum is large enough, then the process stage is ended successfully. 
With reference back to FIG. 15, stage 1534 is then entered to ascertain 
whether the target satellite has been found. If the target satellite has 
not been found, then stage 1538 is entered which causes the increment for 
the scan step to increase by an increment of 1. In stage 1540 a question 
is asked whether the permitted number of scan steps for I has been 
exceeded. If not, stage 1514 is reentered, and during this scan, the 
spiral search pattern now moves a distance v toward point 1410. Again, 
twelve readings are taken, and the antenna is stopped at point 1410 in 
stage 1528. Twelve is a convenient number, and any number could be used 
since this is based on the availability of memory in the SRAM 204. Again, 
the data is processed, and if the satellite is not found in stage 1534, 
the search pattern continues from point 1410 to point 1420 for a distance 
of 2u. 
Assume with respect to FIG. 14 that at point K corresponding to the tenth 
data reading in scan step I=3, a maximum peak is detected in stage 1630 by 
the process data stage 1530, thereby indicating that the target satellite 
is found. The system then moves from stage 1534 to stage 1544, which 
causes the satellite dish antenna 10 to move its boresight to correspond 
to point K. Stage 1550 is then entered. This is the fine-tune stage of the 
present invention. 
As can be seen in FIG. 14, the boresight of the antenna was initially 
positioned to point at J based on calculations using the entered longitude 
and latitude as well as the measured compass reading. The rough-tune 
search automatically seeks the boresight position giving the best signal 
for the selected sub-carrier audio frequency, which as shown in FIG. 14 is 
at point K for purposes of illustration. It is to be expressly understood 
that the teachings of the present invention are not limited to a spiral 
search pattern and that other search patterns could be used. 
10. Fine-Tune Search Pattern 
In FIG. 17, the method used for fine-tuning is illustrated. The bore-sight 
of the antenna 10 is roughly tuned to point K in FIG. 17. K forms the 
center of a rectangular window 1700 that has a dimension of 2n (width) by 
2m (length). K is located in the center of the rectangle 1700. The width 
of the window could be either the azimuth or the elevation direction. 
FIG. 18 sets forth the details of the fine-tune stage 1550. This stage is 
entered at start 1800 and then the first stage 1804 is entered. The 
antenna 10 is directed to align the boresight at point D1, which is on the 
edge of the window 1700. The antenna is scanned along a first line from D1 
through K to D2, which is the opposing edge of the formed window 1700. 
This occurs in stage 1808. One hundred data readings are taken between D1 
and D2, which is determined by stage 1810. This is a significant increase 
in the taking of data samples compared to the rough-tune. The scanning 
continues until the edge of the window D2 is reached in stage 1814. Each 
data reading is read and stored in stage 1818. When 100 readings are 
taken, stage 1820 is entered. The antenna movement is stopped. 
Stage 1530, which is illustrated in FIG. 16, is reentered. If no satellite 
is found in stage 1824, stage 1828 is entered, which causes the antenna 10 
to move back to point K. Stage 1830 is then entered, indicating that the 
fine-tuning has failed. 
However, if the target satellite is found, stage 1840 is entered. Assume, 
for purposes of illustration, that the detected peak is located at point 
L. The boresight of the satellite dish antenna 10 is moved to point L on 
line D1-D2 in stage 1840. The boresight of the antenna 10 is then moved to 
E 1 in stage 1844. The boresight of the antenna 10 is then scanned on line 
El-E2, which is perpendicular to line D1-D2. This occurs in stage 1850. 
One hundred samples are taken as the antenna moves from point E 1 to point 
E2. In stage 1854 the readings taken are stored in stage 1858 until the 
opposing edge E2 of the window is detected in stage 1860. 
Again, the antenna is stopped in stage 1864 and stage 1530 is reentered to 
ascertain the peak. If the peak is not found, then no satellite is found 
in stage 1870, causing the system to enter stage 1874,, which moves the 
antenna back to starting point K and then into stage 1878 indicating that 
the fine-tune failed. However, assume that a peak was located at point M. 
The boresight of the satellite dish antenna 10 is then moved so that it 
aligns with point M in stage 1876. Stage 1880 is entered indicating that 
the fine-tune has worked, and stage 1550 is exited. At this point, and 
with respect to FIG. 17, the precise location of the satellite has been 
obtained. 
Returning to FIG. 15, stage 1550 is exited and stage 1560 is entered 
indicating that the fine-tune has worked. If the fine-tune has not worked, 
as indicated by stages 1830 and 1878 of FIG. 18, then stage 1538 is 
reentered. However, if the fine-tune works, then stage 1570 is entered and 
the satellite is found. The executed search 760 of FIG. 7 is now exited. 
It is to be understood that while the spiral search is used for the rough 
tune and the rectangular search is used for the fine-tune, the system 
would still operate if the two were reversed in order or if two successive 
spiral searches or if two successive rectangular searches were used. 
11. Resynchronize 
Returning now to FIG. 7, stage 770 is entered. When the target satellite is 
found, stage 780 is entered. This is an important part of the present 
invention. Initially the system calculated the position of the target 
satellite in stage 730. This initial calculation assumed a physical zero 
position for C.sub.az and C.sub.el. The term "physical zero" means that 
the system starts at a predetermined fixed count relative to the stowed 
position. However, as can be witnessed with respect to FIGS. 14 and 17, 
the calculated position J of the target satellite did not correlate to the 
final actual peaked position M. Hence, in stage 780, the initial physical 
zero values for C.sub.az and C.sub.el are updated by the microprocessor 
200 so that the calculation occurring in stage 730 would now precisely 
calculate point M. This is an important feature since the user of the 
system can re-stow the antenna 10, and then, upon reinitiation of the 
system, the system will rapidly, in stage 730, fine-tune directly to the 
satellite. This is true if the RV 30 has not moved to a new position. 
Stage 784 is then entered wherein the positions of all the remaining 
satellites are calculated. These calculations occur in the same fashion as 
the calculations in stage 730 occurred except for the relative location of 
the remaining satellites. Stage 790 is then entered wherein the receiver 
60 tunes the system to the precise satellite and transponder selected by 
the user. In other words, the target satellite, although utilized to tune 
the satellite dish antenna 10 to the satellites in the Clarke belt, is 
transparent to the user of the system, who desires only to see the 
satellite and transponder that he has selected. Stage 794 is then entered 
and the search stage 370 is over with. 
Returning to FIG. 3, the picture is displayed in stage 390. It is to be 
expressly understood that the TVRO system of the present invention could 
also be used at a fixed "at-home" installation. 
12. Adjustment of Search Parameters 
In FIG. 19, the user of the present invention has complete control over the 
search parameters for the rough-tune and fine-tune patterns as discussed 
above. FIG. 19 sets forth the search parameter menu displayed on the TV 
70. The menu controls all the operational parameters. 
For example, for the rough-tune, in FIG. 19, the azimuth portion of the 
spiral corresponds to 60 counts and the elevation portion of the spiral 
corresponds to 90 counts. One degree in the azimuth direction contains 10 
counts. I=14, which corresponds to the scan steps. The number of data 
samples taken for each of the scan steps is set to 12. Any of these 
parameters can be suitably adjusted by the user within a range of values. 
Likewise, the fine tune has set the azimuth fine counts equal to 50 and the 
elevation fine window counts equal to 75. Elevation direction is 15 counts 
per degree on average. The azimuth fine steps are 100 and the elevation 
fine steps are 150. Again, any suitable range could be selected by the 
user. Finally, the signal threshold is set to 3. 
13. Polarity Adjustment 
As a final feature of the present invention, this receiver 60 is capable of 
automatically compensating for variations in the polarity settings. This 
is shown in FIGS. 22 and 23. As the vehicle 30 moves, for example, across 
the United States, the polarity setting of the polarotor probe from one 
location to the other location may vary. This would especially be true if 
the vehicle 30 would move from California 2200 to Florida 2210 which would 
represent the extremes. This represents an option that may be provided in 
the receiver 60 of the present invention. This may occur, for example, 
prior to entering search 370 and may be activated as a separate selection 
in menu 400 as shown as item 8 in FIG. 4. The polarity is adjusted so that 
when the search stage 370 is entered, a maximum audio signal will be 
detected. If the polarity is improperly adjusted, then the true peak 
signal will not be detected in either the rough-tune or fine-tune stage. 
To compensate for the polarity setting, a reference satellite 2220 is 
assumed to exist in the Clarke belt 2230. The reference satellite 2220 is 
always assumed to be due south 2240 of the vehicle 30. Hence, the 
following two values of azimuth and elevation are true for the reference 
satellite: 
AZ.sub.r =180.degree. 
EL.sub.r =a value to be calculated 
As fully set forth in the foregoing sections of this application, the 
calculations of the azimuth and elevation angles for the target satellite 
have been determined. Hence, the target satellite has the azimuth (AZ) and 
the elevation (EL) angles. When the system performs the search it 
calculates the polarity for the target satellite based on the initial 
search position which ensures a successful search. After the search is 
completed, the polarities are then calculated for the other satellite 
locations. 
To determine the rotation of the system from the reference satellite so as 
to determine the adjustment to the polarity, the following two 
calculations are used: 
EQU .DELTA.AZ=AZ.sub.r -AZ=180.degree.-AZ 
EQU .DELTA.EL=EL.sub.r -EL 
EQU Total rotation=T.sub.r =.DELTA.AZ+.DELTA.EL 
New polarity settings are set forth in the following two formulas: 
EQU P.sub.v =P.sub.vr +T.sub.r 
EQU P.sub.h =P.sub.v +90.degree. 
where: 
P.sub.v =new vertical polarity 
P.sub.vr =reference vertical polarity 
T.sub.r =total rotation 
P.sub.h =new horizontal polarity 
The value of P.sub.vr is that angle that the system of the present 
invention would have for the vertical polarity of the target satellite if 
the system was placed at the same longitude as the target satellite. In 
the present embodiment, the reference value P.sub.vr is the same for all 
satellites in the Clarke belt and is 170.degree.. 
In FIG. 23, an example of calculating the probe 2310 orientation is set 
forth. Assume satellites A, B, and C are located in the Clarke belt 2230 
of FIG. 22. Satellite A (i.e., 2220a) is the reference satellite and is 
due south of location 2200. Satellite B is east of satellite A and 
satellite C is east of satellite B. In FIG. 23, the dish antenna 2300 has 
a conventional polarotor probe 2310 that must be oriented to allow the 
antenna 2300 to receive signals of either horizontal or vertical polarity. 
In the chart of FIG. 23, the dish antenna 2300 is initially pointed at 
satellite A. The probe 2310 is oriented to match the vertical polarity 
P.sub.v, which is .alpha..sub.A. Under the teachings of the present 
invention, .beta..sub.A is used as the reference angle. As indicated 
above, the vertical polarity, .alpha..sub.A is always 170.degree.. The 
horizontal polarity P.sub.h, .beta..sub.A, is calculated as set forth 
above. When the dish antenna 2300 is pointed at satellite B, the vertical 
polarities match so that .alpha..sub.A equals .alpha..sub.B. However, the 
horizontal polarities .beta..sub.A and .beta..sub.b are not equal. Hence, 
and as set forth above, the difference is calculated as 
.DELTA..alpha.=.beta..sub.B -.beta..sub.A. When the dish antenna 2300 is 
pointed at satellite C, which is east of satellite B, again the vertical 
polarities match, so that .alpha..sub.A=.alpha..sub.B=.alpha..sub.c. 
However, .beta..sub.A, .beta..sub.B, and .beta..sub.c are not equal. 
Hence, the difference, .DELTA..beta.=.beta..sub.c-.beta..sub.A. 
14. Two-Satellite System. 
FIG. 24 provides a flowchart of an alternative method for determining the 
location and bearing of the antenna mount from two geosynchronous 
satellites. This procedure is based on knowing the orbital locations of 
two geosynchronous satellites, determining the azimuth and elevation of 
each satellite from the earth station location, and then calculating the 
latitude, longitude, and bearing of the earth station. Once these 
parameters are known, the azimuths and elevations of all other satellites 
can be calculated. 
Three pieces of data are needed to determine the location and orientation 
of the vehicle 30 relative to the earth and satellites: 
1. Bearing (direction to true north) 
2. Location of the vehicle on the earth's surface (latitude and longitude 
of the satellite antenna mount) 
3. Orientation of the mount to the earth's surface (leveling) 
The mount is initially assumed to be level, since most large RV's have 
leveling devices. Leveling is usually the easiest adjustment to accomplish 
and the easiest for the user to judge accurately. Of the two remaining 
factors, true north is the most difficult to determine and the most 
sensitive variable in locating satellites. 
In this embodiment, system operation begins as previously described in 
section 3 (System Operation). The user turns on the receiver 60 and the TV 
70, and the system becomes initialized at stage 310 in FIG. 3. As before, 
the user is prompted by the target menu 400 and city menu 500 to designate 
an approximate location for the vehicle, which is then used to look up 
estimated longitude and latitude coordinates for the vehicle. The system 
obtains a compass reading from the compass 80 to provide an estimated 
bearing. The longitudes of the two geosynchonous satellites are known 
values that have been permanently stored in the system. Therefore, 
following initialization in stage 2401 of FIG. 24, the following data has 
either been entered or is known by the system: 
SLON.sub.1 =longitude of satellite 1 (S1) 
SLON.sub.2 =longitude of satellite 2 (S2) 
ELON=estimated longitude of vehicle 
ELAT=estimated latitude of vehicle 
EBRG=estimated bearing of vehicle 
AZ.sub.1 =estimated azimuth of satellite 1 
AZ.sub.2 =estimated azimuth of satellite 2 
EL.sub.1 =estimated elevation of satellite 1 
EL.sub.2 =estimated elevation of satellite 2 
The estimated azimuth (AZ.sub.1 and AZ.sub.2) and elevation (EL.sub.1 and 
EL.sub.2) angles for both satellites are calculated from SLON, ELON, and 
ELAT as follows: 
##EQU6## 
where: R=radius of the earth=6367 km; and 
H=height of the satellite about the earth=35800 km 
At stage 2402, the system performs a search by incrementally moving the 
antenna 10 as outlined above in sections 8-10 and FIG. 4-21 to determine 
the actual position of the first satellite. The estimated azimuth and 
elevation for the first satellite (AZ.sub.1 and EL.sub.1) calculated in 
equations (8) and (9) serve as the starting direction for the search. A 
second search is performed to determine the actual position of the second 
satellite in the same manner from AZ.sub.2 and EL.sub.2. After the searchs 
are completed, the following data is known: 
az.sub.1 =actual azimuth for satellite 1 
az.sup.2 =actual azimuth for satellite 2 
el.sub.1 =actual elevation for satellite 1 
el.sub.2 =actual elevation for satellite 2 
The procedure continues by determining whether the location, bearing, and 
leveling data is in error and, if possible, making the necessary 
corrections. To properly position the antenna to the correct azimuth angle 
requires knowledge of the bearing of the antenna mount (EBRG) relative to 
true north. To properly position the antenna 10 to the correct elevation 
angle requires that the antenna mount be level. The vehicle bearing (EBRG) 
is the more probable source of error, and leveling is the less probable 
source of error. This implies that the first test should be for correct 
elevation. Otherwise, if the first test were for correct azimuth, there is 
a significant probability that offsetting errors in location and heading 
could give a false-positive result. 
At stage 2403, the system tests whether the estimated elevation angles of 
both satellites (EL.sub.1 and EL.sub.2) are within predetermined 
tolerances of the actual elevation angles (el.sub.1 and el.sub.2) found in 
the search procedures. If the estimated elevations of both satellites are 
equal to their actual elevations (EL.sub.1 =el.sub.1 and EL.sub.2 
=el.sub.2), then it is likely that the location is correct and the mount 
is level. If the estimated elevations of both satellites are not equal to 
their actual elevations (EL.sub.1 .noteq.el.sub.1 .noteq.or EL.sub.2 
.noteq.el.sub.2), then either: (a) the location is incorrect and the mount 
is level; or (b) the location is correct and the mount is not level; or 
(c) the location is incorrect and the mount is not level. If case (a) 
exists, then the location and, if necessary, the bearing can be corrected 
with the available information. If case (b) or (c) exists, then it is 
indeterminate whether the location or leveling is in error. To determine 
whether case (a) exists, new location data for the mount (ELON and ELAT) 
is derived from el.sub.1 and el.sub.2 at stage 2404, as follows: 
##EQU7## 
At stage 2405, new estimated azimuth angles (AZ.sub.1 and AZ.sub.2) are 
also calculated for both satellites (S1 and S2) from the revised values of 
ELON and ELAT using equation (8) above. 
At stage 2406, the system tests whether the estimated azimuth angles of 
both satellites (AZ.sub.1 and AZ.sub.2) are within predetermined 
tolerances of the actual azimuth angles (az.sub.1 and az.sub.2) found in 
the search procedures. If the estimated azimuths of both satellites are 
equal to their actual azimuths (AZ.sub.1 =az.sub.1 and AZ.sub.2 
=az.sub.2), then case (a) exists and all estimated data is also correct. 
At stage 2410, the system proceeds to calculate the positions of all 
remaining satellites from the verified location and bearing data for the 
antenna mount and the known longitude of each satellite. This procedure is 
discussed in detail above in sections 7 and 8 and equations (8) through 
(11). 
If AZ.sub.1 .noteq.az.sub.1 or AZ.sub.2 .noteq.az.sub.2, then either case 
(a) or (b) may exist. If case (a) exists, then a single correction to the 
bearing (EBRG) will make AZ.sub.1 =az.sub.1 and AZ.sub.2 =az.sub.2. If 
case (b) exists, then a single correction to the bearing will not be 
sufficient, and it is indeterminate whether the location or leveling is in 
error. In the embodiment shown in FIG. 24, the system attempts to 
determine whether case (a) or (b) exists by adjusting the bearing (EBRG) 
at stage 2407. For example, EBRG can be incremented by the average of 
AZ.sub.1 -az.sub.1 and AZ.sub.2 -az.sub.2. The estimated azimuth angles 
(AZ.sub.1 and AZ.sub.2) for both satellites are then recalculated to 
reflect the revised bearing. At stage 2408, if the recalculated estimated 
azimuths of both satellites are still not within the required tolerance of 
their actual azimuths (i.e., AZ.sub.1 .noteq.-az.sub.1 or AZ.sub.2 
.noteq.az.sub.2), then case (b) exists, indicating that the antenna mount 
is not level. In this situation, the system reverts to the 
single-satellite procedure discussed above (stage 2409). 
The present invention is not to be limited by the description of the above 
exemplary embodiment. The configuration of the system of the present 
invention encompasses other embodiments and variations as well as a number 
of differing applications within the scope of the present inventive 
concept as set forth in the following claims.