Title: Coherence frequency determining system and associated radio apparatus
Abstract: The invention provides an apparatus and a method for determining the frequency of a radio frequency signal. The coherency of a received signal is determined and only the frequency of a coherent signal is determined. Zero amplitude transitions of coherent signals are counted in respective time periods. If the counts in each time period agree within a quantization error, the accumulated counts for a fixed time period are employed to determine a frequency. The frequency determining apparatus and method are particularly useful with a frequency agile radio receiver for detecting the presence of radio frequency signals from nearby mobile and stationary transmitters. Upon determination of the frequency of the nearby transmitter, the channel of transmission can be determined from a memory within the receiver and the receiver can be tuned to monitor the transmission. Additional tests to verify the frequency determination may be applied using squelch and window detector circuits of the radio receiver.
Patent Number: 7,006,797 Issued on 02/28/2006 to Sullivan, et al.
| Inventors:
|
Sullivan; Terence Sean (Cambridge, MA);
Brennan; Terence (Melbourne, FL)
|
| Assignee:
|
Counter Technologies, LLC (Ely, NV)
|
| Appl. No.:
|
860506 |
| Filed:
|
May 21, 2001 |
| Current U.S. Class: |
455/67.1; 455/67.11; 455/158.3; 455/226.4 |
| Current Intern'l Class: |
H04B 17/00 (20060101); H04B 1/18 (20060101) |
| Field of Search: |
455/1541,158.3,161.1,173.1,179.1,182.1,184.1,185.1,226.1,226.4,231,234.1,266,69,671.1,450,509,517,550.1,150.1,182.2,183.2,423,339
324/764.8,766.2,766.3
702/75,78
|
References Cited [Referenced By]
U.S. Patent Documents
| 4350950 | Sep., 1982 | Waldmann et al.
| |
| 4651089 | Mar., 1987 | Haigh.
| |
| 4727591 | Feb., 1988 | Manlove.
| |
| 5457716 | Oct., 1995 | Ang et al.
| |
| 5471402 | Nov., 1995 | Owen.
| |
| 5613232 | Mar., 1997 | Toshida et al.
| |
| 5630220 | May., 1997 | Yano.
| |
| 5634205 | May., 1997 | Kurisu et al.
| |
| 5640698 | Jun., 1997 | Shen et al.
| |
| 5710710 | Jan., 1998 | Owen et al.
| |
| 5758296 | May., 1998 | Nakamura.
| |
| 5926752 | Jul., 1999 | Lin.
| |
| 5943606 | Aug., 1999 | Kremm et al.
| |
| 6023615 | Feb., 2000 | Bruckert et al.
| |
| 6335953 | Jan., 2002 | Sanderford et al.
| |
| 6487399 | Nov., 2002 | Rajaniemi et al.
| |
Primary Examiner: Nguyen; Simon
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
The invention claimed is:
1. An apparatus for determining frequency of a radio frequency signal comprising:
a counter for counting zero amplitude transitions of a radio frequency signal
in each of a plurality of time periods of identical duration;
a first register for storing counted zero amplitude transitions for a selected
one of the time periods;
a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends.
2. The apparatus according to claim 1 wherein counting of the zero amplitude
transitions is terminated and the accumulated count is discarded before the total
counting time ends if the counted zero amplitude transitions for any time period
other than the selected time period differ from the counted zero amplitude transitions
for the selected time period by more than the quantization error.
3. The apparatus according to claim 1 wherein counting of the zero amplitude
transitions continues until the total counting time ends and the accumulated count
is discarded after the total counting time ends if the counted zero amplitude transitions
for any time period other than the selected time period differ from the counted
zero amplitude transitions for the selected time period by more than the quantization error.
4. The apparatus according to claim 1 including a prescaler coupled to the counter
for dividing the zero amplitude transitions of the radio frequency signal by a
divisor before supplying the radio frequency signal to the counter.
5. A method of determining frequency of a radio frequency signal comprising:
counting zero amplitude transitions of a radio frequency signal in each of a
plurality of time periods of identical duration;
storing counted zero amplitude transitions for a selected one of the time periods;
storing an accumulated count of zero amplitude transitions during a total counting
time including the plurality of time periods;
comparing counted zero amplitude transitions for each time period other than
the selected time period with the counted zero amplitude transitions for the selected
time period;
discarding the accumulated count if the counted zero amplitude transitions for
any of the time periods other than the selected time period are different from
the counted zero amplitude transitions for the selected time period by more than
a quantization error;
accumulating counted zero amplitude transitions until the total counting time
is reached; and
determining the frequency of the radio frequency signal from the accumulated
count stored when the total counting time is reached.
6. The method according to claim 5 wherein counting of the zero amplitude transitions
is terminated before the total counting time ends and the accumulated count is
discarded if the counted zero amplitude transitions for any time period other than
the selected time period differ from the counted zero amplitude transitions for
the selected time period by more than the quantization error.
7. The method according to claim 5, wherein counting of the zero amplitude transitions
continues until the total counting time ends and the accumulated count is discarded
after the total counting time ends if the counted zero amplitude transitions for
any time period other than the selected time period differ from the counted zero
amplitude transitions for the selected time period by more than the quantization error.
8. The method according to claim 5 including dividing the zero amplitude transitions
of the radio frequency by a divisor before counting the zero amplitude transitions.
9. A radio apparatus comprising:
a radio receiver including
an antenna for collecting electromagnetic energy, and
receiver circuits for processing radio frequency signals received through the
antenna and for producing an output, and
a frequency determining apparatus including
a counter for counting zero amplitude transitions of a radio frequency signal
in each of a plurality of time periods of identical duration;
a first register for storing counted zero amplitude transitions for a selected
one of the time periods;
a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends and the frequency determining
apparatus supplies the frequency determined to the radio receiver for tuning the
radio receiver.
10. The radio apparatus according to claim 9 wherein counting of the zero amplitude
transitions is terminated and the accumulated count is discarded before the total
counting time ends if the counted zero amplitude transitions for any time period
other than the selected time period differ from the counted zero amplitude transitions
for the selected time period by more than the quantization error.
11. The radio apparatus according to claim 9 wherein counting of the zero amplitude
transitions continues until the total counting time ends and the accumulated count
is discarded after the total counting time ends if the counted zero amplitude transitions
for any time period other than the selected time period differ from the counted
zero amplitude transitions for the selected time period by more than the quantization error.
12. The radio apparatus according to claim 9 wherein the radio receiver includes
a squelch detector receiving the output of the receiver circuits and, when a signal
received causes the receiver circuits to produce the output, generating an un-muting
signal for output of sound by the radio receiver, and the radio receiver, in response
to a frequency determination by the frequency determining apparatus, tunes to a
channel including the frequency determined, and determines whether the squelch
detector produces the un-muting signal, and, if not, disregards the frequency determined.
13. The radio apparatus according to claim 9 wherein the radio receiver has a
pass band and includes a window detector receiving the output of the receiver circuits
and indicating whether a received signal is centered within the pass band of the
radio receiver, and the radio receiver, in response to a frequency determination
by the frequency determining apparatus, tunes to a channel including the frequency
determined, determines whether the window detector indicates that the signal is
centered within the pass band of the receiver, and, if not, disregards the frequency determined.
14. The radio apparatus according to claim 9 wherein the radio receiver includes
a memory for storing frequency information in which a channel corresponding to
a frequency determined by the frequency determining apparatus is stored.
15. The radio apparatus according to claim 9 wherein the radio receiver includes
a memory coupled to the tuner for storing frequency information for channels excluded
from reception by the radio receiver wherein, when the frequency determining circuit
determines the frequency of a radio frequency signal that falls within a channel
excluded from reception, the frequency is discarded and the tuner is not tuned
to the channel corresponding to the frequency determined.
16. The radio apparatus according to claim 9 wherein the apparatus includes a
transmitter commonly tuned with the radio receiver for transmitting on an allocated
frequency channel in response to a determination of the frequency of a radio frequency
signal received by the radio apparatus.
17. The radio apparatus according to claim 9 including a bandpass filter connected
from the antenna to the receiver circuits and to the frequency determining apparatus
and including a plurality of bandpass filter elements having respective pass bands
and respectively selected by the radio receiver for individual connection from
the antenna to the receiver circuits and to the frequency determining apparatus.
18. A method of tuning a radio receiver to a channel including a frequency of
a received radio frequency signal comprising:
counting zero amplitude transitions of a radio frequency signal in each of a
plurality of time periods of identical duration;
storing counted zero amplitude transitions for a selected one of the time periods;
storing an accumulated count of zero amplitude transitions during a total counting
time including the plurality of time periods;
comparing counted zero amplitude transitions each time period other than the
selected time period with the counted zero amplitude transitions for the selected
time period;
discarding the accumulated count if the counted zero amplitude transitions for
any of the time periods other than the selected time period are different from
the counted zero amplitude transitions for the selected time period by more than
a quantization error
accumulating counted zero amplitude transitions until the total counting time
is reached;
determining the frequency of the radio frequency signal from the accumulated
count stored when the total counting time ends; and
tuning the radio receiver to a channel including the frequency determined.
19. The method according to claim 18 wherein counting of the zero amplitude transitions
is terminated and the accumulated count is discarded before the total counting
time ends if the counted zero amplitude transitions for any time period other than
the selected time period differ from the counted zero amplitude transitions for
the selected time period by more than the quantization error.
20. The method according to claim 18, wherein counting of the zero amplitude
transitions continues until the total counting time ends and the accumulated count
is discarded after the total counting time ends if the counted zero amplitude transitions
for any time period other than the selected time period differ from the counted
zero amplitude transitions for the selected time period by more than the quantization error.
21. The method according to claim 18 including, after tuning the receiver to
a channel including the frequency determined, determining whether a signal is being
received by the receiver.
22. The method according to claim 18 wherein the receiver has a pass band and
including, after tuning the receiver to a channel including the frequency determined,
determining whether a signal being received is centered within the pass band of
the radio receiver.
23. A method of determining frequency of a received radio frequency signal comprising:
counting zero amplitude transitions of a radio frequency signal received through
an antenna and storing an accumulated count of zero amplitude transitions counted;
determining the frequency of the radio frequency signal received from the accumulated
count of zero amplitude transitions accumulated during a total counting time;
tuning a radio receiver having a pass band to a channel including the frequency
determined; and
after tuning, determining whether a signal is being received within the pass
band of the radio receiver for confirming accuracy of the frequency determined.
24. A radio apparatus comprising:
a radio receiver including
an antenna for collecting electromagnetic energy, and
receiver circuits for processing radio frequency signals received through the
antenna and producing an output and including a tuner tuning only to allocated
frequency channels, and
a frequency determining apparatus for determining the frequency of a radio frequency
signal received from the antenna, wherein the radio receiver includes a memory
coupled to the tuner and to the frequency determining apparatus and storing frequency
information for channels allocated to mobile transmitters and fixed frequency offsets
between channels allocated to mobile transmitters and channels allocated to corresponding
repeater transmitters repeating transmissions of respective mobile transmitters
and, when the radio receiver determines that a channel for which a radio frequency
signal has been received and that the frequency determined by the frequency determining
apparatus is allocated to a mobile transmitter, the tuner of the radio receiver
is tuned to a frequency offset from the channel including the radio frequency signal
for which the frequency has been determined, by the fixed frequency offset stored
in the memory for that channel, for detecting a radio frequency signal transmitted
from a repeater transmitter.
25. The radio apparatus according to claim 24 wherein the frequency determining
apparatus includes
a counter for counting zero amplitude transitions of a radio frequency signal
in each of a plurality of time periods of identical duration;
a first register for storing counted zero amplitude transitions for a selected
one of the time periods;
a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends.
26. A method of tuning a radio receiver comprising:
determining the frequency of a received radio frequency signal at a radio receiver
including a tuner tuning only to allocated frequency channels and a memory coupled
to the tuner and storing frequency information for channels allocated to mobile
transmitters and fixed frequency offsets between the channels allocated to mobile
transmitters and channels allocated to corresponding repeater transmitters repeating
transmissions of respective mobile transmitters; and
determining whether a channel including a frequency that has been determined
from a received radio frequency signal is allocated to a mobile transmitter, and,
if so, tuning the radio receiver to a frequency offset from the channel including
the radio frequency signal for which the frequency has been determined, by the
fixed frequency offset stored in the memory, for detecting a radio frequency signal
transmitted from a repeater transmitter.
27. The method according to claim 26 including determining the frequency of the
received radio frequency signal by
counting zero amplitude transitions of a received radio frequency signal in each
of a plurality of time periods of identical duration;
storing counted zero amplitude transitions for a selected one of the time periods
storing an accumulated count of amplitude transitions during a total counting time
including the plurality of time periods;
comparing counted zero amplitude transitions for each time period other than
the selected time period with the counted zero amplitude transitions for the selected
time period;
discarding the accumulated count if the counted zero amplitude transitions for
any of the time periods other than the selected time period are different from
the counted zero amplitude transitions for the selected time period by more than
a quantization error;
accumulating counted zero amplitude transitions until the total counting time
is reached; and
determining the frequency of the received radio frequency signal from the accumulated
count stored when the total counting time ends.
28. A radio apparatus comprising:
a frequency agile radio receiver including
an antenna for collecting electromagnetic energy,
a bandpass filter connected to the antenna and having a pass band passing radio
frequencies within a first range of radio frequencies, and rejecting frequencies
outside the first range of frequencies;
receiver circuits for processing radio frequency signals received through the
antenna and producing an output,
a radio frequency preamplifier amplifying a radio frequency signal received from
the antenna through the bandpass filter; and
a microprocessor controlling tuning of the frequency agile radio receiver; and
a frequency measuring apparatus for measuring the frequency of a radio frequency
signal received from the antenna and through the bandpass filter and including
a counter for counting zero amplitude transitions of the radio frequency signal
received in each of a plurality of time periods of identical duration;
a first register for storing counted zero amplitude transitions for a selected
one of the time periods;
a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends.
Description
FIELD OF THE INVENTION
The invention concerns an apparatus for determining the frequency of a received
coherent radio frequency signal and a process for determining the frequency of
a coherent radio frequency signal. The apparatus and process are particularly useful
in radio equipment, such as frequency agile radio receivers and transceivers. The
apparatus and method may identify a channel including the frequency determined
for automatically tuning the radio receiver or transceiver to the channel including
the radio frequency signal. By automatically tuning the receiver or transceiver,
a transmission can be monitored or a conversation in progress can be joined.
BACKGROUND
Apparatus for determining the frequency of an electrical signal has long
been known. A conventional apparatus for determining the frequency is usually referred
to as a frequency counter and frequently includes a visual display showing in digital
form the frequency measured. The apparatus typically counts the number of cycles
of an incoming signal during a sampling period. Some of the prior art frequency
counters inhibit display of a count unless the signal detection method used by
the counter indicates that a dominant signal is present in signals input to the
frequency counter.
Frequency agile radio receivers are available that allow a listener to
monitor conversations on each of numerous fixed frequencies. The receiver may monitor
fixed frequencies or channels, tuning one at a time, typically in response to programmed
instructions. These receivers typically include a memory in which frequency information
for tuning the receiver is stored. The receivers are usually programmable for altering
or establishing the stored frequency information and monitoring process. The programming
feature permits the stored frequency information to be changed, for example, in
response to location changes or changes in frequency allocation information. However,
when a frequency agile radio receiver is in operation in an area where there are
many transient transmitters, for example, mobile transceivers. The user of the
frequency agile radio receiver may not know the frequencies of transmission of
the nearby transmitters. The typical receiver is incapable of determining the frequencies
of these transmissions so the receiver cannot tune to monitor them. Since listeners
desire to monitor these nearby transmissions, it is desirable to include, within
the radio, apparatus for determining the channel including the frequency of these
nearby transmissions and, preferably, to provide for manual or automatic tuning
of the radio receiver to that channel for monitoring them.
Some prior art frequency counters for tuning radio receivers have been available
in housings separate from the receivers and connected to the receivers by cables,
making use awkward. Counting of the frequency and tuning of the associated receiver
are disadvantageously slow because the special purpose counters require at least
two complete frequency determinations before producing an output.
Accordingly, there is a need for a frequency determining and radio tuning
apparatus that can rapidly and accurately determine the frequency of a received
radio frequency signal, that can ensure that only the frequency of a coherent signal
is determined, and that, in application to a radio receiver, can tune the receiver
to the channel including the frequency determined before loss of the signal.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a frequency
determining apparatus and method that rapidly determines the frequency of a received
radio frequency signal, measuring the frequency only if the signal is coherent.
It is another object of the invention to provide a frequency determining apparatus
and an interconnected frequency agile radio receiver and a method for automatically
tuning the radio receiver to a channel including a frequency determined by the
frequency determining apparatus.
According to a further object of the invention, a frequency determining
apparatus and an interconnected frequency agile radio receiver determine the frequency
of a received radio frequency signal, determine whether the signal is from a mobile
transmitter, and, is so, tune to receive signals from a repeater transmitter associated
with the mobile transmitter.
Yet a further object of the invention is to provide a frequency determining apparatus
and a frequency agile radio receiver in the same housing and sharing common circuitry.
It is still another object of the invention to provide a radio transceiver incorporating
a frequency determining apparatus and method so that a channel including the frequency
of a received signal is accurately and quickly determined and the transceiver transmitter
and receiver are automatically tuned to the frequency determined for joining an
ongoing conversation.
According to one aspect of the invention, a frequency determining apparatus
includes a counter for counting amplitude transitions of a radio frequency signal
in each of a plurality of time periods of identical duration, a first register
for storing counted zero amplitude transitions for a selected one of the time periods,
and a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends.
According to a second aspect of the invention, the frequency of a radio
signal is determined by counting zero amplitude transitions of a radio frequency
signal in each of a plurality of time periods of identical duration, storing counted
zero amplitude transitions for a selected one of the time periods storing an accumulated
count of zero amplitude transitions during a total counting time including the
plurality of time periods; comparing counted zero amplitude transitions for each
time period other than the selected time period with the counted zero amplitude
transitions for the selected time period, discarding the accumulated count if the
counted zero amplitude transitions for any of the time periods other than the selected
time period are different from the counted zero amplitude transitions for the selected
time period by more than a quantization error, accumulating counted zero amplitude
transitions until the total counting time is reached; and determining the frequency
of the radio frequency signal from the accumulated count stored when the total
counting time is reached.
According to a third aspect of the invention, a radio apparatus comprises
a radio receiver including an antenna for collecting electromagnetic energy, and
receiver circuits for processing radio frequency signals received through the antenna
and for producing an output, and a frequency determining apparatus including a
counter for counting zero amplitude transitions of a radio frequency signal in
each of a plurality of time periods of identical duration, a first register for
storing counted zero amplitude transitions for a selected one of the time periods
a second register for storing an accumulated count of zero amplitude transitions
counted during a total counting time including the plurality of time periods; and
comparing means for comparing counted zero amplitude transitions for each time
period other than the selected time period with the counted zero amplitude transitions
for the selected time period, the second register discarding the accumulated count
if the counted zero amplitude transitions for any of the time periods other than
the selected time period are different from the counted zero amplitude transitions
for the selected time period by more than a quantization error, wherein the frequency
of the radio frequency signal is indicated by the accumulated count stored in the
second register when the total counting time ends and the frequency determining
apparatus supplies the frequency determined to the radio receiver for tuning of
the radio receiver.
According to a fourth aspect of the invention, a radio receiver is tuned
to a channel including a frequency of a received radio frequency signal, the frequency
of the received signal being determined by counting zero amplitude transitions
of a received radio frequency signal in each of a plurality of time periods of
identical duration, storing counted zero amplitude transitions for a selected one
of the time periods storing an accumulated count of zero amplitude transitions
during a total counting time including the plurality of time periods; comparing
counted zero amplitude transitions for each time period other than the selected
time period with the counted zero amplitude transitions for the selected time period,
discarding the accumulated count if the counted zero amplitude transitions for
any of the time periods other than the selected time period are different from
the counted zero amplitude transitions for the selected time period by more than
a quantization error; accumulated counted zero amplitude transitions until the
total counting time is reached; determining the frequency of the received radio
frequency signal from the accumulated count stored when the total counting time
is reached; and tuning the radio receiver to a channel including the frequency determined.
According to a fifth aspect of the invention, the frequency of a received
radio frequency signal is determined by counting zero amplitude transitions of
the radio frequency signal and storing an accumulated count of zero amplitude transitions
counted; determining the frequency of the received radio frequency signal from
the accumulated count of zero amplitude transitions accumulated during a total
counting time; tuning a radio receiver having a pass band to a channel including
the frequency determined; and, after tuning, determining whether a signal is being
received within the pass band of the radio receiver for confirming accuracy of
the frequency determined.
According to a sixth aspect of the invention, a radio apparatus comprises
a radio receiver including an antenna for collecting electromagnetic energy, and
receiver circuits for processing radio frequency signals received through the antenna
and producing an output and including a tuner tuning only to allocated frequency
channels, and a frequency determining apparatus for determining the frequency of
a radio frequency signal received from the antenna, wherein the radio receiver
includes a memory coupled to the tuner and to the frequency determining apparatus
for storing frequency information for channels allocated to mobile transmitters
and frequency offsets between mobile transmitters and repeater transmitters repeating
transmissions of the mobile transmitters and, when the radio receiver determines
that a channel for which a radio frequency signal has been received and the frequency
determined by the frequency determining apparatus is allocated to a mobile transmitter,
the tuner is tuned to a frequency offset from the channel including the radio frequency
signal for which the frequency has been determined, by the offset stored in the
memory, for detecting a radio frequency signal transmitted from a repeater transmitter.
According to a seventh aspect of the invention, a method of tuning a radio
receiver comprises determining the frequency of a received radio frequency signal
at a radio receiver including a tuner tuning only to allocated frequency channels
and a memory coupled to the tuner and storing frequency information for channels
allocated to mobile transmitters and frequency offsets between mobile transmitters
and repeater transmitters repeating transmissions of the mobile transmitters; and
determining whether a channel including a frequency determined from a received
radio frequency signal is allocated to a mobile transmitter, and, if so, tuning
the radio receiver to a frequency offset from the channel including the radio frequency
signal for which the frequency has been determined, by the offset stored in the
memory, for detecting a radio frequency signal transmitted from a repeater transmitter.
According to an eighth aspect of the invention, a radio apparatus comprises
a frequency agile radio receiver including an antenna for collecting electromagnetic
energy, a bandpass filter connected to the antenna and having a pass band passing
radio frequencies within a first range of radio frequencies, and rejecting frequencies
outside the first range of frequencies; receiver circuits for processing radio
frequency signals received through the antenna and producing an output, a radio
frequency preamplifier amplifying a radio frequency signal received from the antenna
through the bandpass filter; and a microprocessor controlling tuning of the frequency
agile radio receiver; and a frequency determining apparatus for determining the
frequency of a radio frequency signal received from the antenna and through the
bandpass filter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a radio receiver apparatus incorporating an embodiment
of the frequency determining apparatus and method according to the invention.
FIG. 2 is a flow chart illustrating the process by which the apparatus of FIG.
1 operates.
FIG. 3 is a flow chart illustrating a frequency determining method according
to an embodiment of the invention.
FIG. 4 is a block diagram of a radio transceiver apparatus incorporating an
embodiment of the frequency determining apparatus and method according to the invention.
DETAILED DESCRIPTION
Radio Receiver with Frequency Determination
FIG. 1 is a block diagram of a frequency agile radio apparatus including an
apparatus for determining the frequency of a radio frequency signal according to
an embodiment of the invention. FIG. 2 is a flow chart illustrating a method of
operation of radio receiver apparatus like that of FIG. 1 according to an embodiment
of the invention. FIG. 3 is a flow chart illustrating the frequency determination
method and apparatus exemplified by FIGS. 1 and 2. In the following description,
emphasis is placed upon use of the invention in connection with a frequency agile
receiver that receives radio frequency signals. However, the invention has several
aspects and is not limited to application in radio receivers. For example, the
frequency determination aspect of the invention may be generally applied to any
frequency determination of a radio frequency signal, for example, through a directly
connected circuit, without the reception of electromagnetic waves propagated from
a transmitting antenna.
In the embodiment of FIG. 1, a radio receiver A that is frequency agile, i.e.,
can be tuned to various frequencies by an internal microprocessor, is interconnected
with a frequency determining apparatus B. The receiver A includes an antenna
1
connected to a bandpass filter
3. The bandpass filter
3 desirably
eliminates unwanted electromagnetic energy, including noise, outside a frequency
range of interest. Further, although shown as a discrete element in FIG. 1, the
bandpass filter
3 may be a part of a radio frequency amplifier or amplifiers
used in conjunction with the filter element rather than a distinct circuit. In
the illustrated embodiment, the bandpass filter
3 includes multiple filter
elements. The illustrated embodiment includes five such filter elements. Each individual
bandpass filter element has a particular pass band, different in frequency range
from the pass bands of the other filter elements. In the illustrated embodiment,
bandpass filter elements
3-
1,
3-
2,
3-
3,
3-
4, and
3-
5 are illustrated. As discussed below, only
one of these filter elements is connected at any particular time for providing
to the signal processing circuitry of the receiver A whatever radio frequency signals
are received at the antenna
1 and that fall within the pass band of the
filter element that is connected at that time.
In a frequency determination mode, each of the bandpass filter elements is connected,
in sequence, for a time sufficient for determining the frequency of a received
signal falling within the pass band of the connected filter element. As a non-limiting
example, when the invention is applied to a radio receiver intended to monitor
communications between transceivers, one or both of which may be mobile or fixed,
the filter element
3-
1 may have a bandpass frequency range of 30-54
MHz. The frequency ranges of the other filter elements may be, for example, 108-136
MHz, 136-174 MHz, 406-512 MHz, and 806-956 MHz. These frequency ranges, as an example,
include standard communication frequency bands and avoid commercial broadcast frequencies.
By describing a bandpass filter with five filter elements, it is not intended to
require a multiple element filter in all or any applications of the invention.
A single bandpass filter or even no bandpass filter may be appropriate for particular
applications of the invention, for example, in simple frequency determinations.
The Frequency Determining Apparatus
The output signal from the bandpass filter
3 is, preferably, amplified
in a radio frequency preamplifier
5 to improve the sensitivity of the apparatus
to relatively weak radio frequency input signals. The amplified radio frequency
signal provided by the preamplifier
5 is supplied to the signal processing
circuitry of the radio receiver A and to the frequency determining apparatus B.
The frequency determining apparatus B includes an optional radio frequency preamplifier
7. This preamplifier
7 is optional in the illustrated receiver because
the preamplifier
5 of the radio receiver may provide sufficient gain for
both the receiver A and the frequency determining apparatus B. In fact, a single
preamplifier may serve both of the frequency determining apparatus and the frequency
agile radio receiver. The joint usage of a single element is an example of one
aspect of the invention in which a commonly housed frequency counter and radio
receiver share many common circuits, providing substantial economies. When the
frequency determining apparatus B stands alone and is not part of nor connected
to a radio receiver, inclusion of the preamplifier
7 is highly desirable
to increase sensitivity and improve overall performance.
The further amplified radio frequency signal from the preamplifier
7 is
supplied to an optional first prescaler
9. When the highest frequency signal
for which the frequency is to be determined is very high, it is useful to divide
the frequency of the signal, i.e., to lower the frequency of the signal to be processed,
before attempting to determine the frequency of the signal. Otherwise, the processing
circuitry for determining the frequency can become quite complicated and expensive,
particularly in processing frequencies, for example, that approach one GHz. The
first prescaler
9 is a commercially available integrated circuit, for example,
the SA701 available from Phillips Semiconductors, Sunnyvale, Calif. Preferably,
the first prescaler
9 has a constant divisor by which it divides the frequency
of the signal supplied to its input, regardless of the frequency, in order to produce
a reduced frequency signal at its output.
It is preferred, in the invention, that the frequency of the signal output by
the first prescaler
9 not exceed about 10 MHz for ease of processing the
output signal from the first prescaler
9 without unusual circuitry. For
example, the divisor of the first prescaler
9 may be set to 128, with regard
to the specific, non-limiting example of the frequency ranges of the bandpass filter
3 previously described, to ensure that the output frequency of the prescaler
does not exceed 10 MHz. In another, less preferred, embodiment, if the divisor
of the first prescaler
9 is variable, for the example for the frequency
ranges provided by the filter elements
3-
1-
3-
5 described
above, the divisor of the first prescaler
9 might be set at 8 for the frequency
range of the filter element
3-
1, 16 for the filter element
3-
2,
32 for the filter element
3-
3, 64 for the filter element
3-
4,
and 128 for the filter element
3-
5. A connection to the first prescaler
9 from the radio receiver A is shown in FIG. 1 that is only present if the
divisor of the first prescaler is variable and controlled in coordination with
the selection of one of bandpass filter elements
3-
1-
3-
5
by the radio receiver.
As shown in FIG. 1, the first prescaler
9 supplies an output signal to
a microcontroller
11 of the frequency determining apparatus B. Since the
preamplifier
7 and the prescaler
9 are both optional, the frequency
determining apparatus B may, in some embodiments, consist only of the microcontroller
11. The microcontroller
11 may be, for example, a PIC 12C672 microprocessor
commercially available from Microchip Technology of Chandler, Ariz. The microcontroller
11 receives the radio frequency signal, adjusted by the preamplifier
7
and the first prescaler
9, if present. The microcontroller
11 provides
an output signal, in the embodiment of FIG. 1, to the radio receiver A.
The Radio Receiver
Turning again to the radio receiver A, the radio receiver A in the portions
now discussed may be entirely conventional, except for the interaction with the
frequency determining apparatus B. For example, the radio signal processing and
control circuits may be those of the Uniden Model BC245XLT, a frequency agile radio
receiver tuned in receiving frequency in response to execution of programmed instructions
by an internal microprocessor. The circuits in the radio receiver that are conventional
are, therefore, only described with respect to their well known functions.
In the radio receiver A, the amplified radio frequency signal from the preamplifier
5 is supplied to conventional receiver circuits
21. The conventional
receiver circuits
21 include, for example, a first detector, a local oscillator
and associated tuner for producing an intermediate frequency (IF) signal, IF amplifier
stages, and a second detector circuit. The output of these conventional receiver
circuits
21 is a demodulated signal including any received audio and a DC
component indicating the location of the received signal within the pass band of
the receiver. The receiver pass band is different from the pass bands of the bandpass
filter
3 and its filter elements
3-
1 3-
5 described
above. The receiver pass band is typically relatively narrow, for example, 25 kHz
in width.
The signal output by the conventional receiver circuits
21 is supplied
to three circuits, namely, a window detector
23, a squelch detector
25,
and an audio amplifier
27. The window detector
23 produces a signal
proportional to the location of the received signal position within the pass band
of the receiver based on the DC component of the output signal of the receiver
circuits
21. The output signal of the window circuit is subjected to a threshold
test in the conventional receiver. In the invention, a second threshold test, independent
of the conventional receiver's threshold test, is applied to determine whether
the signal being received is near the center of the receiver pass band. The squelch
detector
25 indicates whether a signal is being received by the receiver.
The squelch detector
25 produces a two-state output signal, a first output
that is used as a muting signal to prevent audio noise from being heard when no
signal is being received. That noise disappears when a signal is actually being
received by the receiver. In that event, the other state output signal is supplied
by the squelch detector
25 as an un-muting signal that permits the audio
in the signal being received to be reproduced and heard. The un-muting and muting
signals are supplied to and control operation of the audio amplifier
27
so that audio is only heard when a signal is being received. When the squelch and
window detectors indicate that a signal is being received and is within the receiver
pass band, the audio is produced at an audio output device
29. FIG. 1 indicates
output through a speaker as a generic audio output, but headphones and other sound
reproducing apparatus can be employed as well.
The radio receiver A is controlled in its operation by a receiver control microprocessor
31. The microprocessor
31 receives the outputs of the window detector
23 and squelch detector
25, processes their outputs, and sends an
un-muting signal, when appropriate, to the audio amplifier
27. The microprocessor
31 controls frequency tuning of the receiver by sending a tuning signal
to the tuner within the conventional receiver circuits
21. In coordination
with that tuning, the microprocessor controls the particular filter element
3-
1-
3-
5
employed in a particular receiving state in coordination with the tuning of the
receiver circuits
21. Further, a display
33 is connected to the microprocessor
31 to display various information, for example, the channel to which the
radio receiver A is tuned and information used, for example, in programming or
controlling the apparatus generally. Likewise, a keyboard
35 through which
instructions and information are supplied to the apparatus, for example, in programming
and providing other instructions for operation of the radio receiver A, is connected
to the microprocessor
31. Finally, the microprocessor
31 includes
a data port
37 receiving a signal from the microcontroller
11, indicating
a frequency determined by the microcontroller and used in tuning the radio receiver
A as described below. Likewise, the connection provides for sending of control
signals from the microprocessor
31, for example, regarding a frequency to
which the receiver is tuned, to the microcontroller
11. That information
might be used in establishing a divisor of a second prescaler within microcontroller
11 that is described below. The conventional receiver circuits
21
include an oscillator generating a highly precise clock for synthesized tuning
of the receiver A. That clock is preferably also used by the microcontroller
11
so that a second precision oscillator, a relatively expensive circuit, is unnecessary.
The sharing of a common high precision clock circuit between the radio receiver
A and the frequency determining apparatus B is another example of an economy achieved
in an embodiment in which the receiver and frequency determining apparatus are
commonly housed.
Radio Receiver Operation
The operation of the radio receiver A and of frequency determining apparatus
B are described in conjunction with the flow charts of FIGS. 2 and 3. Turning first
to the flow chart of FIG. 2, in step S
1, if there is a multiple element
bandpass filter, one of the filter elements is selected, i.e., a normally open
switch is closed, thereby connecting the selected filter element to the preamplifier
5. The amplified radio frequency signal is also supplied, for the specific
embodiment depicted in FIG. 1, to the preamplifier
7, if present, and, thereafter,
as indicated in step S
2, to the prescaler
9, if present. For the
purposes of this example, it will be assumed that the first prescaler
9,
if present, has a fixed value first divisor. That first divisor of the first prescaler
9 is applied to produce an output signal of reduced frequency as compared
to the input signal in Step S
2. In step S
3, the frequency of the
signal supplied to the microcontroller
11 is determined. That process in
the microcontroller
11 of frequency determination apparatus is described
below in connection with and as part of the description of FIG. 3.
In one embodiment of the specific application being described, the frequency
determined
in step S
3 is employed to tune the radio receiver A to a channel that incorporates
the frequency but may have a center frequency different from the frequency determined
in step S
3 by the microcontroller
11. The tuning of the radio receiver
A is achieved by the receiver control microprocessor
31 in response to a
signal indicating the determined frequency and supplied to the data port
37
of the receiver control microprocessor
31. Once that tuning has been accomplished,
the microprocessor
31 responds to the outputs of one or both of the window
and squelch detectors
23 and
25. One or both of these responses may
be tested. Preferably, the failure of either test, indicating improper tuning,
terminates the frequency determination cycle underway and the process returns to
step S
1.
The output of the squelch detector may be tested to determine if it is a muting
signal or an un-muting signal. If the squelch circuit is quieted by an incoming
signal and produces the un-muting signal, there is confirmation that a signal is
present in the receiver pass band. If the output of the window detector indicates
that a signal being received is near the center of the pass band of the receiver,
then there is initial or further confirmation that the channel corresponding to
the frequency of the received signal has been accurately determined. If any of
whichever of these optional window detector and squelch detector tests is applied
fails, then microprocessor
31 recognizes that no signal is being received
and the radio receiver A may revert to its former tuning. The microprocessor
31
includes a memory and, upon successful verification that a received signal has
been accurately tuned, applying one, both, or neither of the window detector and
the squelch detector tests, the channel of the received signal may be stored in
step S
7 in the memory as frequency information for future reference in monitoring
transmission of the channel.
An important feature of the invention concerns the tuning function. The frequency
determination process operates in the background while the radio receiver A operates
under other control instructions from the microprocessor
31, for example,
fixed in tuning to a channel where a transmission is present or scanning for transmissions
on established channels of interest. In a preferred embodiment, once a preliminary
frequency determination has been made in step S
3 and output to the receiver
controller in step S
4, the receiver is tested in test S
5 to determine
whether the receiver is currently receiving a signal. This test S
5 is made
by checking whether the squelch detector is producing a muting or un-muting signal.
If an un-muting signal is being produced by the squelch detector indicating that
a signal is being received, the process moves to step S
6 where the new frequency
determination is discarded. Then the process returns to step S
1.
If, in test S
5, it is determined that the squelch detector is producing
a muting signal so that no signal is currently being received, then the process
moves to step S
7 and the receiver is tuned to the channel including the
newly determined frequency. Thereafter, the signal on that channel is subjected
to one or both of the squelch detector and window detector tests in test S
8.
Most preferably, at least the squelch detector test is applied. Then, upon passage
of whatever tests are applied at test S
8, the receiver may remain retuned
to monitor the channel including the newly determined frequency and the channel
including the newly determined frequency may be stored in a memory in the receiver
in step S
9. Alternatively, the receiver may resume scanning frequencies
after storing the frequency newly determined. If any of the test or tests applied
at test S
8 are not passed, the process returns to step S
1.
The memory within the receiver control microprocessor
31 may include a
list of frequencies that are within or outside the pass band of the filter
3
but are not to be monitored. Transmissions of paging systems provide one example.
Then, before any automatic retuning of the receiver to a channel including a frequency
determined or storage of a corresponding channel, a comparison is made between
the list of excluded frequencies and the determined frequency. If the frequency
determined or its corresponding channel is in the exclusionary list, then the determined
frequency is discarded and the receiver is not retuned for monitoring or further
testing and verification of the frequency determined and no new channel information
is stored.
The radio receiver and frequency determining apparatus described are particularly
useful in monitoring communications of nearby mobile transmitters. The nearby mobile
transmitters produce relatively strong signals that may be of particular interest
to listeners because the communications concern the area near the listener. With
the invention, these relatively strong signals can be detected and their frequencies
determined. In some communications systems, mobile transmitters do not transmit
and receive directly from a base station but, rather, use higher power repeater
stations as an intermediary. Thus, the low power mobile transceiver effectively
covers a much larger geographical area of communication than its transmitter would
otherwise provide. In many frequency bands, the rules of the Federal Communications
Commission require a fixed offset relationship between the frequencies used by
the mobile units and the repeater frequencies which retransmit transmissions from
the mobile units. Optionally, the memory of the receiver control microprocessor
31 retains information on the frequency offsets of the frequency allocation
rules. Then, upon detection of a mobile transmission, the microprocessor
31
can automatically determine the frequency at which the corresponding repeater channel
transmits and tune the receiver to that frequency where continued reception of
both sides of the communication, i.e., transmissions of both the remote and nearby
party, is more likely. After retuning to the repeater channel, one or both of the
window and squelch tests can be applied to ensu
