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Claims  |
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I claim:
1. Apparatus for receiving and demodulating a satellite broadcast signal,
comprising:
(a) programmable radio frequency tuner/demodulator means for demodulating
said broadcast signal to produce a baseband output signal;
(b) addressable storage means for storing tuning data representative of one
or more tuning frequencies;
(c) data receptor means for receiving address data from an external source;
(d) control means for:
(i) coupling to said data receptor means and decoding said address data to
produce an address of a corresponding storage location within said storage
means;
(ii) extracting said tuning data from said corresponding storage location;
and,
(iii) programming said radio frequency tuner/demodulator means with said
tuning data; and,
(e) video demodulator means for demodulating said baseband output signal to
produce a video output signal, said video demodulator means comprising:
(i) first deemphasis means for deemphasizing said baseband output signal;
(ii) low pass filter means for low pass filtering said deemphasized
baseband output signal;
(iii) first amplifier means for amplifying said filtered, deemphasized
baseband output signal;
(iv) first polarity switching means for controllably switching the polarity
of said amplified, filtered, deemphasized baseband output signal; and,
(v) clamping means for removing dispersion from said amplified, filtered,
deemphasized baseband output signal.
2. Apparatus as defined in claim 1, wherein said video demodulator means is
further for demodulating said baseband output signal to produce an
unclamped, unfiltered baseband output signal, and further comprises:
(a) second deemphasis means for deemphasizing said baseband output signal;
(b) second amplifier means for amplifying the deemphasized baseband signal
output by said second deemphasis means; and,
(c) second polarity switching means, coupled to said first polarity
switching means, for controllably switching the polarity of the amplified,
deemphasized baseband signal output by said second amplifier means to
produce said unclamped, unfiltered, baseband output signal.
3. Apparatus as defined in claim 1, wherein said video demodulator means is
further for demodulating said baseband output signal to produce an
unclamped, unfiltered baseband output signal, and further comprises:
(a) second deemphasis means for deemphasizing said baseband output signal;
(b) second amplifier means for amplifying the deemphasized baseband signal
output by said second deemphasis means; and,
(c) second polarity switching means, coupled to said first polarity
switching means, for controllably switching the polarity of the amplified,
deemphasized baseband signal output by said second amplifier means to
produce said unclamped, unfiltered, baseband output signal;
and wherein said control means is further for:
(d) receiving polarity switching data from said external source; and,
(e) transmitting said polarity switching data to said first and second
polarity switching means, thereby causing the polarity of said video
output signal and the polarity of said unclamped, unfiltered, baseband
output signal to adopt a state represented by said polarity switching
data.
4. Apparatus for receiving and demodulating a satellite broadcast signal,
comprising:
(a) programmable radio frequency tuner/demodulator means for demodulating
said broadcast signal to produce a baseband output signal;
(b) addressable storage means for storing tuning data representative of one
or more tuning frequencies;
(c) data receptor means for receiving address data from an external source;
(d) control means for:
(i) coupling to said data receptor means and decoding said address data to
produce an address of a corresponding storage location within said storage
means containing first audio tuning data for tuning said first frequency
audio tuner/demodulator means;
(ii) extracting said first audio tuning data from said corresponding
storage location;
(iii) programming said first audio frequency tuner/demodulator means with
said first audio tuning data; and,
(e) first programmable audio frequency tuner/demodulator means for
demodulating said baseband output signal to produce a first audio output
signal, said first programmable audio frequency tuner/demodulator means
further comprising:
(i) first voltage controlled oscillator means for producing a first local
oscillator output signal having a frequency determined by an input
reference signal;
(ii) first reference oscillator means for producing a first fixed frequency
reference output signal;
(iii) first programmable divider means for receiving said first audio
tuning data and for dividing said first local oscillator output signal by
an amount determined by said first audio tuning data;
(iv) first programmable reference divider means for receiving said first
audio tuning data and for dividing said first fixed reference frequency
output signal by an amount determined by said first audio tuning data;
(v) first comparator means for comparing the frequency of signals output by
said first programmable divider means with the frequency of signals output
by said first programmable reference divider means and for producing an
output signal representative of the difference between said signal
frequencies, said difference comprising said first voltage controlled
oscillator input reference signal;
(vi) signal mixing means for mixing said baseband output signal with said
local oscillator output signal to produce an intermediate frequency output
signal;
(vii) first bandpass filter means for bandpass filtering said intermediate
frequency output signal to produce a filtered intermediate frequency
output signal;
(viii) first switchable bandpass filter means for bandpass filtering said
intermediate frequency output signal within a narrow frequency pass band
to produce a narrowly filtered intermediate frequency output signal;
(ix) second switchable bandpass filter means for bandpass filtering said
intermediate frequency output signal within a wide frequency pass band to
produce a widely filtered intermediate frequency output signal; and,
(x) filter switching means for controllably actuating one or the other of
said first and second switchable bandpass filter means.
5. Apparatus as defined in claim 4, wherein said control means is further
for:
(a) receiving filter switching data from said external source; and,
(b) transmitting said filter switching data to said filter switching means,
thereby actuating one or the other of said first and second switchable
bandpass filters.
6. Apparatus for receiving and demodulating a satellite broadcast signal,
comprising:
(a) programmable radio frequency tuner/demodulator means for demodulating
said broadcast signal to produce a baseband output signal;
(b) addressable storage means for storing tuning data representative of one
or more tuning frequencies;
(c) data receptor means for receiving address data from an external source;
(d) control means for:
(i) coupling to said data receptor means and decoding said address data to
produce an address of a corresponding storage location within said storage
means;
(ii) extracting said tuning data from said corresponding storage location;
and,
(iii) programming said radio frequency tuner/demodulator means with said
tuning data;
(e) first programmable audio frequency tuner/demodulator means for
demodulating said baseband output signal to produce a first audio output
signal;
(f) second programmable audio frequency tuner/demodulator means for
demodulating said baseband output signal to produce a second audio output
signal;
(g) data demodulator means for demodulating said second audio output signal
to produce a data output signal said data demodulator means further
comprising:
(i) first amplifier means for amplifying said second audio output signal to
produce an amplified replica thereof;
(ii) voltage level shifting means for shifting the voltage level of said
amplified replica signal; and,
(iii) comparator means for comparing the width of signal pulses output by
said voltage level shifting means with a reference pulse width and for
adjusting the width of said signal pulses to equal said reference pulse
width. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention pertains to the adaptation of computers to the reception and
demodulation of satellite broadcast signals. More particularly, the
invention provides receiver/demodulator apparatus for interfacing between
a computer and a satellite communication receiving antenna.
BACKGROUND OF THE INVENTION
There has been a widespread proliferation of satellite communications
systems in recent years. Many consumers have acquired satellite
communications equipment for home reception of satellite broadcast
television signals, and many businesses have acquired such equipment for
the purpose of receiving and/or transmitting useful business data.
However, proper configuration and use of conventional satellite
communications equipment can require considerable technical skill beyond
the capabilities of the average consumer or business person.
The present invention simplifies the configuration and usage of satellite
communications equipment so that a relatively unskilled consumer or
business person can obtain maximum advantage from such equipment with
comparatively little effort. This is accomplished by equipping a computer
with special purpose hardware and software, so that the computer may
control all facets of the satellite communications operation in a manner
which the user can easily define and readily adapt to changing situations.
The hardware consists of a complete audio, video and data satellite
receiver/demodulator built onto one IBM/PC compatible peripheral
card-sized circuit board. Power and tuning information is obtained from
the computer's system bus. Data received from the satellite may be
supplied to the computer via an RS-232 compatible serial interface. The
hardware provides baseband output which is compatible with either the
VC/II, B-MAC, or OAK descrambling systems; 950 to 1450 megahertz ("MHz")
digitally synthesized RF tuning; compatibility with both the C and Ku
satellite communication bands; two separate digitally synthesized audio
channels, one of which can be used to demodulate frequency shift keyed
("FSK") data at rates up to 9600 baud; programmable audio and RF tuning,
as well as programmable audio bandwidths and video invert; a capability to
disable all programmable functions with a special system electronically
programmable read only memory ("EPROM"); and, an on-board 20 volt power
converter for supplying power to a satellite receiver's low noise block
down-converter ("LNB").
SUMMARY OF THE INVENTION
In a preferred embodiment, the invention provides apparatus for receiving
and demodulating a satellite broadcast signal, comprising a programmable
radio frequency tuner/demodulator for demodulating the broadcast signal to
produce a baseband output signal; a video demodulator for demodulating the
baseband output signal to produce a video output signal; a first
programmable audio frequency tuner/demodulator for demodulating the
baseband output signal to produce a first audio output signal; a second
programmable audio frequency tuner/demodulator for demodulating the
baseband output signal to produce a second audio output signal; and, a
data demodulator for demodulating the second audio output signal to
produce a data output signal.
Preferably, the apparatus includes addressable storage means for storing
tuning data representative of one or more tuning frequencies; data
receptor means for receiving address data from an external source such as
a computer; and, a control means for decoding the address data to produce
the address of a corresponding storage location within the storage means,
extracting the tuning data from that corresponding storage location, and
then programming the radio frequency tuner/demodulator with the tuning
data.
Advantageously, a voltage controlled oscillator is provided for producing a
local oscillator output signal having a frequency determined by an input
reference signal. A reference oscillator is also provided to produce a
fixed frequency reference output signal. A programmable divider divides
the local oscillator output signal by an amount determined by the
aforementioned tuning data, and a programmable reference divider divides
the fixed reference frequency output signal by an amount which is also
determined by the tuning data. A comparator compares the frequency of
signals output by the programmable divider with the frequency of signals
output by the programmable reference divider and produces an output signal
representative of the difference between said signal frequencies, said
difference comprising the voltage controlled oscillator's input reference
signal.
The first programmable radio frequency tuner/demodulator preferably
includes a signal mixer for mixing the baseband output signal with the
local oscillator output signal to produce an intermediate frequency output
signal, a bandpass filter for bandpass filtering the intermediate
frequency output signal to produce a filtered intermediate frequency
output signal, an intermediate frequency amplifier for amplifying the
filtered intermediate frequency output signal, an automatic gain control
means for controlling the gain of the intermediate frequency amplifier,
and a signal demodulator for demodulating the amplified, filtered
intermediate frequency output signal.
The video demodulator advantageously includes a first deemphasis circuit
for deemphasizing the baseband output signal, a low pass filter for low
pass filtering the deemphasized baseband output signal, a first amplifier
for amplifying the filtered, deemphasized baseband output signal, a first
polarity switcher for controllably switching the polarity of the
amplified, filtered, deemphasized baseband output signal, and a clamp for
removing dispersion from the amplified, filtered, deemphasized baseband
output signal.
Preferably, the video demodulator is also capable of demodulating the
baseband output signal to produce an unclamped, unfiltered baseband output
signal. This is accomplished, in the preferred embodiment, with the aid of
a second deemphasis circuit for deemphasizing the baseband output signal,
a second amplifier for amplifying the deemphasized baseband signal output
by the second deemphasis circuit, and a second polarity switcher, coupled
to the first polarity switcher, for controllably switching the polarity of
the amplified, deemphasized baseband signal output by the second amplifier
to produce the unclamped, unfiltered, baseband output signal.
First and second programmable audio frequency tuner/demodulators are
provided for demodulating the baseband output signal to produce first and
second audio output signals respectively. The aforementioned control means
assists by decoding the address data to produce the addresses of
corresponding storage locations within the storage means containing tuning
data for tuning the first and second audio tuner/demodulators, extracting
the audio tuning data from the corresponding storage locations, and
programming the audio frequency tuner/demodulators with the audio tuning
data. Each of the two audio tuner/demodulators incorporates a voltage
controlled oscillator which produces a local oscillator output signal at a
frequency determined by an input reference signal. Separate reference
oscillators produce first and second fixed frequency reference output
signals respectively. A pair of programmable dividers receive the audio
tuning data and divide the local oscillator output signals by amounts
which are determined by the audio tuning data. A pair of programmable
reference dividers also receive the audio tuning data and divide the fixed
reference frequency output signals by amounts which are also determined by
the audio tuning data. A pair of comparators compare the frequency of
signals output by the programmable dividers with the frequency of signals
output by the programmable reference dividers and produce output signals
representative of the difference between the signal frequencies, these
differences comprising the voltage controlled oscillator input reference
signals.
A pair of signal mixers mix the baseband output signal with the local
oscillator output signals to produce a pair of intermediate frequency
output signals. Separate first bandpass filters bandpass filter the
intermediate frequency output signals to produce a pair of filtered
intermediate frequency output signals. A first pair of switchable bandpass
filter are provided for bandpass filtering the intermediate frequency
output signals within a narrow frequency pass band to produce a pair of
narrowly filtered intermediate frequency output signals. A second pair of
switchable bandpass filters are provided for bandpass filtering the
intermediate frequency output signals within a wide frequency pass band to
produce a pair of widely filtered intermediate frequency output signals. A
filter switching means controllably actuates one or the other of each pair
of first and second switchable bandpass filters.
The data demodulator incorporates a first amplifier for amplifying the
second audio output signal to produce an amplified replica thereof, a
voltage level shifter for shifting the voltage level of the amplified
replica signal, and a comparator for comparing the width of signal pulses
output by the voltage level shifter with a reference pulse width and for
adjusting the width of the signal pulses to equal the reference pulse
width.
The control means preferably also functions to receive polarity switching
data from the external source (i.e. computer) and to transmit the polarity
switching data to the first and second polarity switchers, thereby causing
the polarity of the video output signal and the polarity of the unclamped,
unfiltered, baseband output signal to adopt the state represented by the
polarity switching data. The control means further functions to receive
filter switching data from the external source (i.e. computer) and to
transmit the filter switching data to the filter switching means, thereby
actuating one or the other of the first and second switchable band-pass
filters.
The data output signal may contain tuning data for programming the radio
frequency tuner/demodulator, the first and second audio
tuner/demodulators, in which case, the control means preferably also
functions to decode the address data to produce the addresses of
corresponding storage locations within the storage means containing tuning
data for tuning each of the tuner/demodulators, to extract the tuning data
from those storage locations, and to program each of the
tuner/demodulators with the appropriate corresponding tuning data. In such
case, coupling means are provided for coupling the data output signal to
the control means, thereby facilitating remote programming of the various
tuner/demodulators.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is a plan view of a satellite communications receiver/demodulator
constructed in accordance with the preferred embodiment of the invention
and illustrates the principal functional components of the apparatus. FIG.
1(b) is an end view of the receiver/demodulator of FIG. 1(a), showing the
input/output connections and the manner in which the apparatus is
connected to a satellite communications antenna, descrambler and monitor.
FIG. 2 is similar to FIG. 1(a), but shows selected circuit components in
greater detail.
FIG. 3 depicts the Main Selection Menu displayed by the system software on
the user's computer screen to simplify the user's interaction with the
apparatus.
FIG. 4 depicts the Configuration File Maintenance Menu displayed by the
system software on the user's computer screen to simplify the user's
creation, modification and storage of configuration files containing
parameters for use in selected satellite signal reception situations.
FIG. 5 depicts the Change Configuration Menu displayed by the system
software on the user's computer screen to further simplify the user's
creation, modification and storage of configuration files containing
parameters for use in selected satellite signal reception situations.
FIG. 6 depicts the Satellite Communication Menu displayed by the system
software on the user's computer screen to simplify the user's initiation
of satellite signal reception and to simplify the user's storage, printing
or displaying of data received from a satellite.
FIG. 7 is a functional block diagram of the RF tuner/demodulator of the
preferred embodiment.
FIG. 8 is a functional block diagram of the video demodulator/filter of the
preferred embodiment.
FIG. 9 is a functional block diagram of one channel of the receiver audio
section of the preferred embodiment.
FIG. 10 is a functional block diagram of the data demodulator of the
preferred embodiment.
FIG. 11 is a functional block diagram of the digital control circuitry of
the preferred embodiment.
FIG. 12 is a circuit schematic diagram of the analog circuitry of the
preferred embodiment.
FIG. 13 is a circuit schematic diagram of the digital circuitry of the
preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment will first be described from the point of view of
a typical user. A detailed technical description of the preferred
embodiment will then be provided.
Operation by Typical User
Overview
The invention provides, on a single circuit card, apparatus capable of
receiving and demodulating video, audio and/or data signals broadcast from
a satellite and which can be installed in an IBM PC- or AT- compatible
computer. By integrating several functional units onto a single circuit
card, and by using the computer to perform communication control and data
capture functions, the invention facilitates reduced cost, miniaturized
satellite communications. With the aid of an appropriate antenna and low
noise block downconverter (neither of which comprise part of the present
invention), the apparatus can be tuned to receive signals at any frequency
in either the C or Ku communication bands. The receiver's tuning functions
are controllable, with the aid of special purpose software, directly from
the computer's bus; or can be hardware selected in a manner which prevents
alteration by the computer. Potentially, the receiver's tuning functions
may even be programmed by data incorporated in a data stream received from
the satellite. Video and stereo audio outputs are provided by the
receiver. Data received from the satellite is routed to an RS-232 serial
data output port for use by the computer or other applications hardware.
System Description
The apparatus functions and their interrelationship with one another will
now be described with reference to FIGS. 1(a) and 1(b).
Satellite Reception
Audio, video, and data signals are transmitted to satellite 10 from a
remote uplink site 11 in the frequency range of either 6 gigahertz ("GHz")
or 14 Ghz. These signals are received by satellite 10, which is in
geostationary orbit over the earth's equator. Satellite 10 re-broadcasts
the signals toward the earth at a lower frequency of either 4 Ghz (the "C"
communications band) or 12 Ghz (the "Ku" communications band). The
rebroadcast signals are receivable by users at "earth stations" or
"downlink sites" distributed over a wide area on the earth's surface; for
example, over all of North America in the case of most satellites likely
to be of interest to users situate in North America.
A downlink site incorporates a satellite receiving antenna dish 12
(probably less than about 1.8 meters in diameter) which focuses the
satellite signal onto a feedhorn 14 which guides the signal, with the
correct polarization, to a low noise block downconverter ("LNB") not
shown, but associated with feedhorn 14). The LNB amplifies the signal to
usable levels and converts it to an intermediate frequency ("IF") band.
For C band communications, the signal reaching the LNB is in the 3.7 to
4.2 GHz range, and is down-converted by the LNB to the 950 to 1450 MHz IF
range. For Ku band communications, the satellite signal reaches the LNB in
the 11.7 to 12.2 GHz range, and is again converted by the LNB to the 950
to 1450 MHz IF range. This lower frequency range IF signal can easily be
fed indoors via inexpensive coaxial cable 16, and thence coupled to
receiver/demodulator 18 (which is mounted inside a computer--not shown).
RF Tuner/Demodulator
The IF signal output by the LNB is fed directly into RF tuner/demodulator
20, which in turn supplies power to the LNB via cable 16. RF
tuner/demodulator 20 amplifies and filters the IF signal, then tunes to a
specific transponder frequency within the IF band (each transponder
frequency band is usually 36 MHz wide) to yield a second IF signal. Tuning
is accomplished with the aid of a crystal controlled phase locked loop
("PLL") circuit. Once the signal is converted to the second IF (612 MHz)
band, it is conditioned through a 24 MHz filter and demodulated to produce
a baseband signal. RF tuner/demodulator 20 is a completely shielded metal
unit. The tuner can be programmed in 1 MHz increments to tune any
frequency within the first (i.e. 950 to 1450 Mhz) IF band.
Video Processing
The baseband signal demodulated by the PLL tuner is used to produce video
and audio signals; and, a de-emphasized version of the baseband signal for
external descrambler connection. The output signal provided at video
connector 22 has been clamped, filtered, de-emphasized and amplified. On
the other hand, the output signal provided at baseband connector 24 has
only been de-emphasized and amplified.
Audio Processing
The baseband signal output by RF tuner/demodulator 20 is also input to
audio "A" and "B" tuner/demodulator circuits 26 and 28 respectively. The
audio signals are on separate sub-carriers, so additional tuners are
needed to receive them. Two independent audio tuners are provided, to
facilitate reception of direct stereo broadcasts. Each tuner provides a
filtered and amplified 600 ohm output.
Audio B tuner/demodulator 28 also acts, in conjunction with data
demodulator 32, as a data tuner/demodulator. When tuner/demodulator 28 is
set to receive a sub-carrier bearing FSK modulated data, the demodulated
data is converted to RS-232 compatible voltage and current levels, and
output via 9-pin D-type female connector 30. To access this data, the user
need only connect a serial data cable between connector 30 and computer
19's serial data input port.
Controlling the Satellite Receiver
The RF tuning, and either of the Audio A or Audio B sub-carrier tuner
frequencies, can be set by simply writing the appropriate value into the
proper hardware register, addressed as a PC I/O port. This can be done
either with the aid of the system software, as hereinafter described in
greater detail; or, with the aid of custom application software developed
by the user. More particularly, with the aid of the system software, the
user may create and modify a "configuration file" containing data
parameters representative of: (a) the video carrier frequency, and whether
the video signal is to be inverted or not; (b) the two audio sub-carrier
frequencies, and whether they are to be processed by wide or narrow
bandwidth filters; and, (c) the frequency of the local oscillator in the
LNB.
After creating a configuration file as aforesaid, the user indicates, via
the system software, that satellite signal reception is to commence. The
system software transmits the pre-defined data parameters from the
configuration file to receiver 18, causing communications to commence in
the manner defined by the user's data parameters. At any time, the user
may change the data parameters, causing the system software to transmit
the new parameters to receiver 18, thereby altering the communication
process in the appropriate manner.
Processing Received Data
Data routed to serial data communications port 30 can be processed by
computer 19 either with the aid of the system software, or with the aid of
custom application software developed by the user. Using the system
software, the user can specify the characteristics of the serial port, and
direct that the received data be displayed on monitor 21, sent to a
printer, or saved in a disk file for later processing. The software allows
the user to alter the data destination at any time, and to stop reception
of data at any time.
Configuring the Apparatus for Specific Services
All communication, data storage and other parameters are stored on disk in
configuration files accessible by computer 19. There may be any number of
such files stored on disk for various satellite channels, data rates, data
formats, etc. At any one time there will be only one configuration file
active, defining the "current" communication parameters. With the aid of
the system software, the user first selects a configuration file, which
becomes the "current" configuration; then initiates satellite signal
reception. The user may change configuration files at any time, for
example in order to change the parameters of the serial data communicated
via port 30; to alter the signal frequencies and sub-carriers the
apparatus is to use; etc. The system software also enables the user to
add, change, delete, or print selected configuration files.
Because the communication parameters are programmable, and because the
apparatus can receive data demodulated from the satellite signal, a
satellite service could potentially remotely reconfigure some or all of
the communication parameters from uplink site 11. This would merely
require the use of a means for coupling data signals received from
satellite 10 back into computer 19, so that computer 19 could use the data
to reprogram the operation of rece | | |
