US2188068A - Modulated carrier wave television and like transmitter - Google Patents

Modulated carrier wave television and like transmitter Download PDF

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Publication number
US2188068A
US2188068A US73420A US7342036A US2188068A US 2188068 A US2188068 A US 2188068A US 73420 A US73420 A US 73420A US 7342036 A US7342036 A US 7342036A US 2188068 A US2188068 A US 2188068A
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United States
Prior art keywords
transmitter
carrier wave
carrier
modulated carrier
synchronising
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Expired - Lifetime
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US73420A
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English (en)
Inventor
Tringham William Stuart Leader
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RCA Corp
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RCA Corp
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Filing date
Publication date
Application filed by RCA Corp filed Critical RCA Corp
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Publication of US2188068A publication Critical patent/US2188068A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/04—Synchronising
    • H04N5/06—Generation of synchronising signals
    • H04N5/067—Arrangements or circuits at the transmitter end
    • H04N5/0675—Arrangements or circuits at the transmitter end for mixing the synchronising signals with the picture signal or mutually

Definitions

  • This invention relates to modulated carrier wave television and like transmitters and more particularly tosuch transmitters of the ⁇ kind wherein synchronising signals which aretransmitted as modulations of the 'same carrier wave as that upon which the picture signals are transmitted correspond with a value of transmitted carrier which is low as compared with any value the said transmitted carrier has between synchronising periods'.
  • the object of the present invention is to provide an improved television transmitter oi the kind referred to whereby the transmitted carrier may be reduced to zero during synchronising periods without having to provide inconveniently large synchronising pulses.
  • a modulated carrier wave television or like transmitter of the kind referred to comprises a shaping circuit such that the effect of the bottom bend of the static charactistic of the modulated stage is corrected for,
  • the shaping circuit operating to cause the decrease in carrier strength which is caused by the application tothe modulatorl of modulating signals above a predetermined value at least equal to the black picture signal value to be disproportionf5 ally large as compared to the decrease in transmitted carrier strength which occurs consequent upon the application of modulating signals below the said black picture signal value.
  • Fig. l there is illustrated the static characteristic modulation curve of the stage at which modulation is effected.
  • This curvey shows the relationship between the direct current Voltage impressed on the grid of thel tubes in the modulating stage and the high frequency output of the modulator.
  • the curve hastwo knees.
  • the lower section ofthe curve, wherein the D. C. grid volt input is small, has a lower b-end B1 and the curve then straightens out into a substantially linear section identified as S, and then has an upper bend or knee identified as B2. Accordingly, it is seen that for low values of input grid voltage to the modulator the high frequency output changes very slowly up to a certain value.
  • the ⁇ increase in ⁇ high frequency output changes substantially proportional to the changein D. C. grid voltage input, and then approaches a value which maybe termed a saturation value where there is little, if any, change in high frequency output regardless of the D.v C. grid voltage input.
  • the anodes AI, A2, A3 of these valves being connected to the grid point (no-t shown) of the carrier frequency amplifier (not shown) at which modulation is to beeffected and the cathodes C1 C2 C3 of these valves being connected to the negative terminal HT- of a suitable source (not shown) of anode potential whose positive terminal HT+ is earthed.
  • the anodes of the modulator valves are also connected through the usual modulator resistance MR. in series with the correcting diode D to earth. Synchronising pulses correspond' to f high anode feed to the modulator valves, for, in
  • the voltage drop across the modulator anode resistance MR is applied to the grid of the modulated amplifier stage (not shown) so that variations of anode feed of the modulator valves eiTect a variation of grid bias on the modulated ⁇ ampliiier stage while the same end of the modulator resistance is connected to the anodes of the modulators as is connected to the grid of the modulated ampliery stage.
  • the anode feed produces a negative voltage at this end of the resistance with respect to the other.
  • synchronizing pulses correspond to high anode feed to the modulator valves, and since by suitably choosing the circuit constants, it is ⁇ possible to make the correcting diode D operate as a non-rectilinear impedance, it is possible to make the amplification of the synchronising pulses suiciently greater than that of the picture signals to produce a required disproportionate modulation by the said pulses such that the carrier becomes zero during the said pulses.
  • the diode D should be of low impedance and have an anode current-anode voltage characteristic such that the said diode begins to saturate at a value corresponding to a value somewhat in excess of the peak picture signal value, ipe. the value corresponding to picture black. Since the synchronising signals are blacker than black the action will be the ordinary substantially rectilinear action as regards picture signals, but when the more powerful synchronising ⁇ signals occur the carrier transmitted will be brought down to zero.
  • non-rectilinear impedance other than a diode may be used, if desired.
  • a modulated carrier Wave television transmitter of the kind referred to comprising a modulating valve having a control electrode, a modulating load resistance in series with a non-rectilinear impedance in the anode circuit of said valve, means for controlling a carrier frequency stage at which modulation is to be effected by the voltage drop across said load resistance, and means for applying input signals constituting picture signals and superimposed synchronizing signals to the control electrode of the modulating valve, a characteristic of said non-rectilinear impedance being such that it saturates at signal values slightly in excess of peak picture signals so as to cause disproportionally greater amplication of said pulses whereby, as a result of such disproportionate amplification, the carrier amplitude is reduced Substantially to Zero by synchronizing pulses of lesser magnitude than would otherwise be necessary.
  • a modulating carrier wave television transmitter comprising a modulating valve having a control electrode, a modulating load resistance in series with a non-rectilinear impedance comprising the diode in the anode circuit of said valve, means for controlling the carrier frequency stage at which modulation is to be effected b-y the voltage drop across said load resistance, and means for applying input signals consisting of picture signals and superimposed synchronizing pulses to the control electrode of said modulating valve, the characteristic of said diode being such that its circuit acts as a shaping circuit to cause disproportionally greater amplification of said pulses whereby, as a result of such disproportionate amplication, the carrier amplitude is reduced substantially to zero by synchronizing pulses 'of ⁇ lesser magnitude than would otherwise be necessary.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Amplitude Modulation (AREA)
US73420A 1935-04-10 1936-04-09 Modulated carrier wave television and like transmitter Expired - Lifetime US2188068A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2188068X 1935-04-10

Publications (1)

Publication Number Publication Date
US2188068A true US2188068A (en) 1940-01-23

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ID=10900693

Family Applications (1)

Application Number Title Priority Date Filing Date
US73420A Expired - Lifetime US2188068A (en) 1935-04-10 1936-04-09 Modulated carrier wave television and like transmitter

Country Status (2)

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US (1) US2188068A (fr)
FR (1) FR804635A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2761919A (en) * 1950-12-06 1956-09-04 Emi Ltd Non-linear automatic contrast control circuit for video amplifier

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2761919A (en) * 1950-12-06 1956-09-04 Emi Ltd Non-linear automatic contrast control circuit for video amplifier

Also Published As

Publication number Publication date
FR804635A (fr) 1936-10-28

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