CA1067154A - Carrier isolation system - Google Patents
Carrier isolation systemInfo
- Publication number
- CA1067154A CA1067154A CA250,515A CA250515A CA1067154A CA 1067154 A CA1067154 A CA 1067154A CA 250515 A CA250515 A CA 250515A CA 1067154 A CA1067154 A CA 1067154A
- Authority
- CA
- Canada
- Prior art keywords
- carrier
- wave
- frequency
- carrier wave
- filter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
S P E C I F I C A T I O N
CARRIER ISOLATION SYSTEM
ABSTRACT OF THE DISCLOSURE
A circuit is described for operating on a carrier wave in a transmission signal including a reduced carrier with a single sideband. The carrier wave is isolated, limited, divided in frequency by a predetermined amount, and then restricted in frequency by a band pass filter. The output of the band pass filter is then multiplied in frequency. After this, the carrier wave is mixed with the sideband frequencies and the signal is demodulated.
CARRIER ISOLATION SYSTEM
ABSTRACT OF THE DISCLOSURE
A circuit is described for operating on a carrier wave in a transmission signal including a reduced carrier with a single sideband. The carrier wave is isolated, limited, divided in frequency by a predetermined amount, and then restricted in frequency by a band pass filter. The output of the band pass filter is then multiplied in frequency. After this, the carrier wave is mixed with the sideband frequencies and the signal is demodulated.
Description
la~7ls4 - .
This invention relates to electronic communication systems. In particular the invention relates to a carrier isolation system in a receiver for amplitude modulated carrier waves.
. S BACKGROUND OF THE INVENTION
~4~
Many communication systems require the isolation of the carrier portion of the modulated wave. For example, in reduced carrier (A3A) transmission the carrier is transmitted along with the sideband frequencies at a reduced amplitude, generally 10 to 20 db below the peak sideband level. In many situations, this carrier wave is used to demodulate the sideband signal in a product demodulator. This insures that the recovered frequency components will be accurate and will protect the system against frequency errors due to the frequency doppler shifts. Such systems have been in use for communication for many years and have generally given good , service.
one of the problems connected with this type of transmission system is that it is necessary that the band ~ 20 width of the isolating filter be wide enough to follow drift ; and frequency errors but narrow enough so that desired side--~ band components do not disturb the performance of the system.
This re~uires, in single sideband systems, that the carrier filter pass only the desired frequency plus or minus a shift of 100 Hz. In most transmitters which carry voice frequencies, the frequency response is restricted so that the lowest audio frequency is greater than 300 Hz. If the transmitter filter circuits are sufficiently selective and are stable, this system works fairly well.
''~
.,~
~ lQ67154 However, there are some cases where the low pass -filter has changed, due to temperature changes or aging, and there is some response at frequencies as low as 50 Hz. Also, there are cases where the carrier fre~uency drifts to the -edge of the sideband filter, thereby permitting the low frequency components of the sideband to fall within the pass-. band of the carrier filter. In this case, the sideband ~ components will produce objectional phase modulation components ; and introduce distortion. The invention described herein greatly reduces this problem, making such systems relatively free of such difficulties.
The invention is based upon the fact that frequency division or re~uency multiplication does not change the ;i spacing of the sideband frequencies relative to the carrier.
For example, if a single-sideband transmitter is modulated ; with a 100 cycle tone, the lowest separation between the sideband and the carrier is 100 Hz. This separation is main-tained no matter how many times the signal is multiplied or divided in frequency.
In the Marine radio telephone field, a specification of - lO0 cycles per second for the accuracy of the carrier frequency has been standardized for certain types of modula-tion. For this reason, the band width of the carrier channel , ~
must be at least + 100 Hz in order to handle the transmissions properly. Since it is possible that the transmitter carrier - wave be at the edge of its tolerance, say 100 Hz low, upper : sideband components at 200 Hz from the carrier just pass the `;` selectivity re~uirement~ These sideband components may be ,. . .~- fairly strong and, since in the A3A transmission the carrier is at least 10 db below the sideband, it is possible that distortion may result.
'' ' . .
B
~671S4 The basic idea of the invention is to divide the frequency of the carrier fre~uency wave. Frequency division reduces the amount of frequency error which is permissible in the system. The carrier wave is first filtered by a crystal filter having a band width of + 100 Hz. Then, the resulting wave is passed through a limiter to remove all traces of amplitude modulation and then the carrier frequency is divided by 8 by any of the known division circuits. If the original carrier had a frequency of 100 KHz, the divided wave has a ; 10 frequency of 12.5 KHz. A fre~uency error at the inputfrequency of 100 Hz will now be an error of 12.5 Hz. The band pass filter which lies between the dividing and multi-plying circuits should have a band width of only - 12.5 Hz.
; An ordinary band pass circuit filter can be used for this purpose, but it is believed that a phase locked loop is preferable. Other active circuits, such as a locked oscillator, have been considered, but it is believed that the phase locked loop is the best. The phase locked loop as used in this situation acts like a tracking filter which follows frequency errors witnin the range of + 12.5 Hz; however, due to the circuitry that restricts its speed, effectively cuts off undesired sideband components.
; Additional details of the invention will be disclosed in the following description, taken in connection with the ' 25 accompanying drawings.
,, .
` SUMMARY OF THE INVENTION
','', ,..: ' In accordance with the invention, in a receiver for amplitude-modulated carrier waves, there is provided a carrier ` isolation system for separating a carrier wave from undesired accompanying components. The system comprises a carrier wave ` B
. . , . . ~ ., . ... .. .. .- . - . ..
1~671S4 . ...
filter connected to a source of amplitude modulated wave signal for passing substantially only the carrier frequency :
wave, said filter having a frequency width sufficient to accomodate the expected carrier frequency shifts. A frequency divider circuit connected to the filter for dividing the carrier frequency wave by a predetermined amount. A bandpass filter connected to the output of the divider circuit for restricting the divided frequency wave to a predetermined , :
variation and thereby attenuate undesired frequency components.
; 10 A new system also includes a multiplying circuit coupled to the bandpass filter for multiplying the frequency of the "
carrier wave by the same factor as used by the divider circuit to restore the carrier wave to its original frequency. `-Finally, the system includes a demodulation circuit connected , to the multiplying circuit and the source of modulated wave ; 3ignal for demodulating said wave signal to produce an audio ~ frequency wave signal.
, "~
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope be pointed out -~ in the appended claims.
"., :. .
~ BRIEF DESCRIPTION OF THE DRAWINGS
..... .
` Figure l is a schematic wiring diagram in block showing -one embodiment of the invention.
Figure 2 is a schematic wiring diagram also in block ,.......................................................................... . .
showing the addition of a phase locked loop which may be used instead of the band pass filter in Figure l.
. .
. .
Figure 3 is a graph showing the frequency and amplitude relations between the carrier wave and the region in which !
; - 4 ~B
. . - . .. : . . .
~Q67154 sideband waves can exist. This figure is for the normal ;-reduced carrier with single sideband (A3A). ~
Figure 4 is a graph similar to Figure 3, but showing - -the carrier wave after having been divided by 8 and a side-band region also having l/8 the normal frequency values.
, DETAILED ~ESCRIPTION
Referring now to Figure l, input terminal 10 indicates the connections which are to be made to a circuit which supplies an incoming SSB modulated wave. This signal is . . ~
applied to a carrier filter 12 and to a sideband filter 13.
The carrier filter 12 may be very narrow but the sideband filter 13 must have considerable band width since it must pass frequencies which include from 100.2 KHz to 102.5 KHz, this , region being indicated by the rectangle 14 in Figure 3. The ~, 15 carrier filter 12 is rated to pass a nominal 100 KHz wave, but due to the frequency instability of some of the sending ~ components, the filter must pass fre~uencies within the range ; of 100 KHz + 100 Hz, this range and amplitude being indicated by the rectangle 15 in Figure 3.
~ 20 The output of the carrier filter 12 is applied to a i limiter 16 which removes all traces of amplitude modulation -~ i there be any. The output of the limiter 16 is then applied to a divider circuit 17 which divides the frequency by 8.
.. ..
~,; This divider may be a three-stage bistable multivibrator or any other well known divider means. The frequency in the ~` output circuit of this divider is a nominal 12, 500 Hz, but it , is subject to the same percentage variation as the input or 12.5 cycles per second. The output of this divider circuit 17 is indicated by the narrow rectangle 18 in Figure 4, this wave .
' '~
:, . ... ~ . : . ... . . . . . . .
. : . ., .: , . ~, - .. . . . ;~ . . . :.
:
being applied to a band pass filter circuit 20 which may be ~-a crystal filter.
The output from the band pass filter is now applied to a multiplier circuit 21 which multiplies the frequency by ; 5 8 and produces the same carrier frequency as the original input signal. This wave is next applied over conductor 22 to a product demodulator 23. The demodulator 23 also receives sideband frequencies from filter 13. The output from the demodulator 23 may be amplified by an audio amplifier 25 and then sent to terminal 26 and a load 27 which may be a loud :' speaker or a voice recorder.
The phase locked loop 24 is an alternate circuit for use in filtering the signal after division and may be used , instead of circuit 20. This circuit 24 is shown in Figure 2 ;, 15 and includes a phase detector 30, a low pass filter 31, and a voltage controlled oscillator 32. The phase locked loop as used in this circuit acts like a tracking filter which will ' follow frequency errors due to the 12.5 cycles per second variations, yet due to the circuitry that restricts its speed, ' 20 it effectively attenuates all the sideband components lying outside the desired the desired range.
The phase detector 30 receives one of its inputs from the divider circuit 17. The other input comes from the -voltage controlled oscillator 32 and is a 12.5 KHz wave. The '' 25 oscillator 32 is part of the loop 24 and receives its input energy from the low pass filter 31. The filter 31 receives its energy from the phase detector 30. The range of frequencies passed by this loop circuit is determined by the cut-off re~uency of the low pass filter 31. A typical cut-off re~uency is 25 Hz. Thé output of the filter 31 controls the ,~ ',, , _ ~; _ 1~67154 frequency of the oscillator 32 which is sent back to the phase detector 30, thereby closing the loop.
It should be noted that the region 14 in Figure 3 and a similar region 33 in Figure 4 are areas where the sideband waves may occur. When there is no modulation of the carrier, ~ there is no wave energy at all in this range. When a pure ; tone o say 500 Hz modulates the carrier at a 50 percent modulation, a single sideband 34 having a frequency of 100,500 Hz and a relative amplitude of .5 results. Both sideband - 10 regions 14 and 33 are drawn to indicate a sideband range of 200 Hz to 2.5000 Hz.
The essence of the invention is contained in the ~ -:, process of segregating the carrier wave from its sideband components, dividing its fre~uency by an integer factor greater than one, iltering the resulting wave by the use of a narrow efficient filter, multiplying the filtered wave by the same .. -:
integer factor, and combining the resultant carrier wave with ; the sideband components.
Although various embodiments of the invention have .
been described herein in detail it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.
:', , t ", .~
This invention relates to electronic communication systems. In particular the invention relates to a carrier isolation system in a receiver for amplitude modulated carrier waves.
. S BACKGROUND OF THE INVENTION
~4~
Many communication systems require the isolation of the carrier portion of the modulated wave. For example, in reduced carrier (A3A) transmission the carrier is transmitted along with the sideband frequencies at a reduced amplitude, generally 10 to 20 db below the peak sideband level. In many situations, this carrier wave is used to demodulate the sideband signal in a product demodulator. This insures that the recovered frequency components will be accurate and will protect the system against frequency errors due to the frequency doppler shifts. Such systems have been in use for communication for many years and have generally given good , service.
one of the problems connected with this type of transmission system is that it is necessary that the band ~ 20 width of the isolating filter be wide enough to follow drift ; and frequency errors but narrow enough so that desired side--~ band components do not disturb the performance of the system.
This re~uires, in single sideband systems, that the carrier filter pass only the desired frequency plus or minus a shift of 100 Hz. In most transmitters which carry voice frequencies, the frequency response is restricted so that the lowest audio frequency is greater than 300 Hz. If the transmitter filter circuits are sufficiently selective and are stable, this system works fairly well.
''~
.,~
~ lQ67154 However, there are some cases where the low pass -filter has changed, due to temperature changes or aging, and there is some response at frequencies as low as 50 Hz. Also, there are cases where the carrier fre~uency drifts to the -edge of the sideband filter, thereby permitting the low frequency components of the sideband to fall within the pass-. band of the carrier filter. In this case, the sideband ~ components will produce objectional phase modulation components ; and introduce distortion. The invention described herein greatly reduces this problem, making such systems relatively free of such difficulties.
The invention is based upon the fact that frequency division or re~uency multiplication does not change the ;i spacing of the sideband frequencies relative to the carrier.
For example, if a single-sideband transmitter is modulated ; with a 100 cycle tone, the lowest separation between the sideband and the carrier is 100 Hz. This separation is main-tained no matter how many times the signal is multiplied or divided in frequency.
In the Marine radio telephone field, a specification of - lO0 cycles per second for the accuracy of the carrier frequency has been standardized for certain types of modula-tion. For this reason, the band width of the carrier channel , ~
must be at least + 100 Hz in order to handle the transmissions properly. Since it is possible that the transmitter carrier - wave be at the edge of its tolerance, say 100 Hz low, upper : sideband components at 200 Hz from the carrier just pass the `;` selectivity re~uirement~ These sideband components may be ,. . .~- fairly strong and, since in the A3A transmission the carrier is at least 10 db below the sideband, it is possible that distortion may result.
'' ' . .
B
~671S4 The basic idea of the invention is to divide the frequency of the carrier fre~uency wave. Frequency division reduces the amount of frequency error which is permissible in the system. The carrier wave is first filtered by a crystal filter having a band width of + 100 Hz. Then, the resulting wave is passed through a limiter to remove all traces of amplitude modulation and then the carrier frequency is divided by 8 by any of the known division circuits. If the original carrier had a frequency of 100 KHz, the divided wave has a ; 10 frequency of 12.5 KHz. A fre~uency error at the inputfrequency of 100 Hz will now be an error of 12.5 Hz. The band pass filter which lies between the dividing and multi-plying circuits should have a band width of only - 12.5 Hz.
; An ordinary band pass circuit filter can be used for this purpose, but it is believed that a phase locked loop is preferable. Other active circuits, such as a locked oscillator, have been considered, but it is believed that the phase locked loop is the best. The phase locked loop as used in this situation acts like a tracking filter which follows frequency errors witnin the range of + 12.5 Hz; however, due to the circuitry that restricts its speed, effectively cuts off undesired sideband components.
; Additional details of the invention will be disclosed in the following description, taken in connection with the ' 25 accompanying drawings.
,, .
` SUMMARY OF THE INVENTION
','', ,..: ' In accordance with the invention, in a receiver for amplitude-modulated carrier waves, there is provided a carrier ` isolation system for separating a carrier wave from undesired accompanying components. The system comprises a carrier wave ` B
. . , . . ~ ., . ... .. .. .- . - . ..
1~671S4 . ...
filter connected to a source of amplitude modulated wave signal for passing substantially only the carrier frequency :
wave, said filter having a frequency width sufficient to accomodate the expected carrier frequency shifts. A frequency divider circuit connected to the filter for dividing the carrier frequency wave by a predetermined amount. A bandpass filter connected to the output of the divider circuit for restricting the divided frequency wave to a predetermined , :
variation and thereby attenuate undesired frequency components.
; 10 A new system also includes a multiplying circuit coupled to the bandpass filter for multiplying the frequency of the "
carrier wave by the same factor as used by the divider circuit to restore the carrier wave to its original frequency. `-Finally, the system includes a demodulation circuit connected , to the multiplying circuit and the source of modulated wave ; 3ignal for demodulating said wave signal to produce an audio ~ frequency wave signal.
, "~
For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope be pointed out -~ in the appended claims.
"., :. .
~ BRIEF DESCRIPTION OF THE DRAWINGS
..... .
` Figure l is a schematic wiring diagram in block showing -one embodiment of the invention.
Figure 2 is a schematic wiring diagram also in block ,.......................................................................... . .
showing the addition of a phase locked loop which may be used instead of the band pass filter in Figure l.
. .
. .
Figure 3 is a graph showing the frequency and amplitude relations between the carrier wave and the region in which !
; - 4 ~B
. . - . .. : . . .
~Q67154 sideband waves can exist. This figure is for the normal ;-reduced carrier with single sideband (A3A). ~
Figure 4 is a graph similar to Figure 3, but showing - -the carrier wave after having been divided by 8 and a side-band region also having l/8 the normal frequency values.
, DETAILED ~ESCRIPTION
Referring now to Figure l, input terminal 10 indicates the connections which are to be made to a circuit which supplies an incoming SSB modulated wave. This signal is . . ~
applied to a carrier filter 12 and to a sideband filter 13.
The carrier filter 12 may be very narrow but the sideband filter 13 must have considerable band width since it must pass frequencies which include from 100.2 KHz to 102.5 KHz, this , region being indicated by the rectangle 14 in Figure 3. The ~, 15 carrier filter 12 is rated to pass a nominal 100 KHz wave, but due to the frequency instability of some of the sending ~ components, the filter must pass fre~uencies within the range ; of 100 KHz + 100 Hz, this range and amplitude being indicated by the rectangle 15 in Figure 3.
~ 20 The output of the carrier filter 12 is applied to a i limiter 16 which removes all traces of amplitude modulation -~ i there be any. The output of the limiter 16 is then applied to a divider circuit 17 which divides the frequency by 8.
.. ..
~,; This divider may be a three-stage bistable multivibrator or any other well known divider means. The frequency in the ~` output circuit of this divider is a nominal 12, 500 Hz, but it , is subject to the same percentage variation as the input or 12.5 cycles per second. The output of this divider circuit 17 is indicated by the narrow rectangle 18 in Figure 4, this wave .
' '~
:, . ... ~ . : . ... . . . . . . .
. : . ., .: , . ~, - .. . . . ;~ . . . :.
:
being applied to a band pass filter circuit 20 which may be ~-a crystal filter.
The output from the band pass filter is now applied to a multiplier circuit 21 which multiplies the frequency by ; 5 8 and produces the same carrier frequency as the original input signal. This wave is next applied over conductor 22 to a product demodulator 23. The demodulator 23 also receives sideband frequencies from filter 13. The output from the demodulator 23 may be amplified by an audio amplifier 25 and then sent to terminal 26 and a load 27 which may be a loud :' speaker or a voice recorder.
The phase locked loop 24 is an alternate circuit for use in filtering the signal after division and may be used , instead of circuit 20. This circuit 24 is shown in Figure 2 ;, 15 and includes a phase detector 30, a low pass filter 31, and a voltage controlled oscillator 32. The phase locked loop as used in this circuit acts like a tracking filter which will ' follow frequency errors due to the 12.5 cycles per second variations, yet due to the circuitry that restricts its speed, ' 20 it effectively attenuates all the sideband components lying outside the desired the desired range.
The phase detector 30 receives one of its inputs from the divider circuit 17. The other input comes from the -voltage controlled oscillator 32 and is a 12.5 KHz wave. The '' 25 oscillator 32 is part of the loop 24 and receives its input energy from the low pass filter 31. The filter 31 receives its energy from the phase detector 30. The range of frequencies passed by this loop circuit is determined by the cut-off re~uency of the low pass filter 31. A typical cut-off re~uency is 25 Hz. Thé output of the filter 31 controls the ,~ ',, , _ ~; _ 1~67154 frequency of the oscillator 32 which is sent back to the phase detector 30, thereby closing the loop.
It should be noted that the region 14 in Figure 3 and a similar region 33 in Figure 4 are areas where the sideband waves may occur. When there is no modulation of the carrier, ~ there is no wave energy at all in this range. When a pure ; tone o say 500 Hz modulates the carrier at a 50 percent modulation, a single sideband 34 having a frequency of 100,500 Hz and a relative amplitude of .5 results. Both sideband - 10 regions 14 and 33 are drawn to indicate a sideband range of 200 Hz to 2.5000 Hz.
The essence of the invention is contained in the ~ -:, process of segregating the carrier wave from its sideband components, dividing its fre~uency by an integer factor greater than one, iltering the resulting wave by the use of a narrow efficient filter, multiplying the filtered wave by the same .. -:
integer factor, and combining the resultant carrier wave with ; the sideband components.
Although various embodiments of the invention have .
been described herein in detail it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.
:', , t ", .~
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a receiver for amplitude-modulated carrier waves a carrier isolation system for separating a carrier wave from undesired accompanying components comprising:
(a) a carrier wave filter connected to a source of an amplitude modulated wave signal for passing substantially only the carrier frequency wave signal, said filter having a frequency width sufficient to accommodate the expected carrier frequency shifts;
(b) a frequency divider circuit connected to the filter for dividing the carrier frequency wave by a pre-determined amount;
(c) a bandpass filter connected to the output of the divider circuit for restricting the divided frequency wave to a predetermined variation and thereby attenuate undesired frequency components;
(d) a multiplying circuit coupled to the bandpass filter for multiplying the frequency of the carrier wave by the same factor as used by the divider circuit to restore the carrier wave to its original frequency; and (e) a demodulation circuit connected to the multiplying circuit and the source of modulated wave signal for demodulating said wave signal to produce an audio frequency wave signal.
(a) a carrier wave filter connected to a source of an amplitude modulated wave signal for passing substantially only the carrier frequency wave signal, said filter having a frequency width sufficient to accommodate the expected carrier frequency shifts;
(b) a frequency divider circuit connected to the filter for dividing the carrier frequency wave by a pre-determined amount;
(c) a bandpass filter connected to the output of the divider circuit for restricting the divided frequency wave to a predetermined variation and thereby attenuate undesired frequency components;
(d) a multiplying circuit coupled to the bandpass filter for multiplying the frequency of the carrier wave by the same factor as used by the divider circuit to restore the carrier wave to its original frequency; and (e) a demodulation circuit connected to the multiplying circuit and the source of modulated wave signal for demodulating said wave signal to produce an audio frequency wave signal.
2. A carrier isolation system according to Claim 1 wherein an amplitude limiter circuit is connected between the carrier wave filter and the frequency divider circuit for eliminating traces of amplitude modulation from the carrier wave.
3. A carrier isolation system according to Claim 1 wherein the bandpass filter is a phase locked loop circuit.
4. A carrier isolation system according to Claim 3 wherein said phase locked loop circuit includes a phase detector, a low pass filter, and a voltage controlled oscillator.
5. A carrier isolation system according to Claim 3 wherein said frequency divider circuit includes a plurality of bistable multivibrator circuits connected in tandem.
6. A carrier isolation system according to Claim 3 wherein said demodulation circuit is a product demodulator, including means for combining the sideband waves with the restored carrier wave, and a rectifying means.
7. A carrier isolation system according to Claim 1 wherein said demodulation is also connected to a sideband filter circuit coupled to the source of the modulated wave, said sideband filter circuit arranged for passing only the sideband waves.
8. A method of eliminating undesired frequency waves which exist in close proximity to the carrier wave of an amplitude modulated transmitted signal, comprising the following: filtering the modulated wave to separate the carrier wave from the sideband frequencies; dividing the frequency of the carrier wave by a factor greater than one;
filtering the divided wave to remove said undesired frequency waves; multiplying the divided wave by the same factor used in dividing to restore the original carrier frequency wave;
mixing the restored carrier wave and the sideband wave; and demodulating the result to produce an audio signal wave.
filtering the divided wave to remove said undesired frequency waves; multiplying the divided wave by the same factor used in dividing to restore the original carrier frequency wave;
mixing the restored carrier wave and the sideband wave; and demodulating the result to produce an audio signal wave.
9. A method according to Claim 8 wherein the carrier wave is limited after the filtering action to remove all traces of amplitude modulation.
10. A method of operating on a received amplitude modulated carrier wave so as to reduce unwanted noise and undesired frequency waves, comprising the following steps:
(a) filtering the carrier wave from the aplitude modulated wave.
(b) dividing the carrier wave frequency by a factor greater than unity.
(c) filtering the divided carrier wave to reduce the noise and unwanted frequencies adjacent to the carrier wave, and (d) multiplying the resulting carrier wave frequency by the same factor used in division to restore the original carrier wave frequency.
(e) and demodulating the received modulated wave with the restored carrier.
(a) filtering the carrier wave from the aplitude modulated wave.
(b) dividing the carrier wave frequency by a factor greater than unity.
(c) filtering the divided carrier wave to reduce the noise and unwanted frequencies adjacent to the carrier wave, and (d) multiplying the resulting carrier wave frequency by the same factor used in division to restore the original carrier wave frequency.
(e) and demodulating the received modulated wave with the restored carrier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA250,515A CA1067154A (en) | 1976-04-20 | 1976-04-20 | Carrier isolation system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA250,515A CA1067154A (en) | 1976-04-20 | 1976-04-20 | Carrier isolation system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1067154A true CA1067154A (en) | 1979-11-27 |
Family
ID=4105735
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA250,515A Expired CA1067154A (en) | 1976-04-20 | 1976-04-20 | Carrier isolation system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1067154A (en) |
-
1976
- 1976-04-20 CA CA250,515A patent/CA1067154A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5483695A (en) | Intermediate frequency FM receiver using analog oversampling to increase signal bandwidth | |
| US2283575A (en) | High frequency transmission system | |
| US4078245A (en) | System for multiplexing information channels adjacent to a video spectrum | |
| GB2124842A (en) | Radio receiver including a frequency-locked loop and a muting circuit | |
| US4811425A (en) | Apparatus for reducing the effects of local oscillator leakage in mixers employed in zero IF receivers | |
| US4310920A (en) | Single sideband AM-FM stereo modulation system | |
| US4622694A (en) | Transmission system for TV signals on radio links | |
| US3973203A (en) | Carrier isolation system | |
| US3873931A (en) | FM demodulator circuits | |
| US4270221A (en) | Phaselocked receiver with orderwire channel | |
| CA1067154A (en) | Carrier isolation system | |
| US4249038A (en) | Stereo decoder with 19KHz-pilot suppression and improved oscillator phase locking | |
| US3706946A (en) | Deviation modifier | |
| CA1083678A (en) | Carrier wave recovery circuit | |
| US3182132A (en) | Doppler frequency shift correction of information band frequencies in a suppressed carrier system using a pair of pilot signals | |
| US4406922A (en) | Stereo broadcast system | |
| JPS6130347Y2 (en) | ||
| JPH0740645B2 (en) | Frequency modulation detector | |
| EP0720315B1 (en) | Method for narrow band frequency modulation or phase modulation; transmitter and receiver for carrying out the method | |
| JP3640669B2 (en) | Circuit device for derivation of sound quality signal depending on sound quality of received multiplexed signal | |
| US4409436A (en) | Stereo pilot signal eliminating circuit for AM stereophonic receiver | |
| JPS6239858B2 (en) | ||
| EP0222863B1 (en) | Fm feedback demodulator using injection-locked oscillator | |
| EP1066677B1 (en) | Electronic circuits | |
| GB2122827A (en) | Radio receiver including a muting circuit |