Abstract: To minimize carrier leak in the modulation of voice frequencies to the desired line frequency for a carrier system, a first balanced modulator is operated at a low frequency where low carrier-leak modulators may be constructed and a second balanced modulator, directly coupled to the first, is employed. The modulation frequency of said second modulator is very high compared to that of said low-frequency modulator. The sideband obtained from the second modulation stage is remote from said high-frequency carrier and a band-pass filter selects the desired sideband and substantially eliminates the high-frequency carrier and the other sideband. Thus, only a low amplitude of carrier leak is present which may cause interference with other channels.

Abstract: A forward error correcting digital transmission system having two separate transmission channels carrying redundant information. The signal on the first channel is encoded by combining each present bit with itself delayed m bits in time. The signal on the second channel may be encoded in the same manner only with a delay of n bits in time, or left without coding, i.e., n=0, in any case m and n are unequal integers. Both first and second channels are transmitted over separate transmission paths to the receiving terminal where each is independently decoded to obtain the original binary information from each received encoded signal.If an error is introduced into one of the channels during transmission, the encoded information necessarily contains an error in the present bit and its associated m or n delayed bit.

Abstract: Deviation of a frequency modulated oscillator (FMO) is set by applying a square wave test signal to the input of the oscillator so as to generate a predetermined amount of symmetrical periodic frequency shift above and below the rest frequency, i.e., the carrier frequency of the FMO, for a desired setting of the FMO's modulation sensitivity. The FMO frequency is divided down so as to be within the range of a programmable divider in the automatic phase control circuit of the oscillator. The carrier frequency is set by program switches which are connected to an interface logic unit that provides the control information to set the divisor of the programmable divider. During testing, the square wave test signal is also applied to a control input of the interface logic unit, for adjusting the divisor so as to provide at the output a binary signal having a predetermined pulse repetition rate when the modulated signal is applied to the input to the programmable divider and the deviation is correctly set.

Abstract: An APC (automatic phase control) circuit is utilized to measure the linearity of an FMO (frequency modulated oscillator). In accordance with a common APC concept a programmable divider is connected to an output of said frequency modulatable oscillator to produce a binary output signal having a predetermined pulse repetition rate. This signal is compared with a reference oscillator signal in a phase control comparator producing a DC control signal which is applied to the control input of said frequency modulated oscillator to maintain the average oscillator frequency constant. This DC control voltage gives an indication of average free running frequency of the oscillator.To measure linearity, the said binary signal at the programmable divider output is also further divided and processed to produce a low frequency square waveform which is applied via a manual ON/OFF switch and a modulation amplifier to the modulation input of the said FMO.

Abstract: A linearity test signal generator alternately provides a burst of a modulation frequency and no modulation to the modulation input of the frequency modulator oscillator (FMO) under test. A programmable divider is connected to the output of said frequency modulated oscillator to produce a binary output signal which is applied to the automatic phase control circuit. This circuit in turn develops a DC control signal which is applied to the control input of said frequency modulated oscillator to maintain the average oscillator frequency constant. This DC control voltage gives an indication of the shift in the average free running frequency of the oscillator while being modulated, caused by oscillator non-linearity. The voltage is first sampled when the oscillator is unmodulated to produce a reference voltage which is stored and then compared to a sample of the DC control voltage when the oscillator is being modulated.

Abstract: An input signal is applied to the inverting input of a class B amplifier and to the input of a limiter circuit. The square wave signal from the limiter is applied to the input of a switching amplifier which drives this amplifier between V and ground at the switching rate established by the input signal; thereby, obtaining a power control signal. The power control signal is applied to one terminal of a load and to the non-inverting input of said class B amplifier. Ignoring the input signal to the amplifier, this switches the output of the class B amplifier between V and ground at the same rate and in phase with the output from the switching amplifier. The gain of the input signal path in the amplifier is such that the input signal will just drive the output between V and ground. The switching action of the power control signal in combination with the input signal then causes the output signal across the load to have the same characteristic as the input signal but with a peak-to-peak amplitude of 2V.

Abstract: A 70.+-..DELTA.f MHz sinusoidal test signal from a standard radio link test set is down converted and shaped to obtain a 35.+-..DELTA.f/2 MHz sinusoidal test signal to be applied to the radio set under test. The output of the radio set is applied to an up converter in which a multiplier is used that maintains the amplitude information as it doubles the frequency. The 70.+-..DELTA.f MHz test signal from the up converter is then applied to the input of the radio link test set, and the characteristic is measured as if the radio set under test employed a 70 MHz IF, rather than a 35 MHz IF.

Abstract: In a microstrip frequency modulated oscillator, the linearity of the modulating circuit incorporating a varactor diode is adjusted by using a microstrip transmission line as a secondary resonator in conjuction with a variable reactor. The varactor is connected to one end of this resonator which end is also connected to the main resonator of the microstrip oscillator. The variable reactor is connected between the other end of the secondary resonator and ground.

Abstract: The baseband input to a frequency modulation radio transmitter is switchably connectable to a square wave generator, the amplitude of the square wave output being adjusted to provide a predetermined deviation of the FM radio transmitter. The output frequency of a pilot oscillator is also applied to the baseband input and is subjected to amplitude modulation because of non-linearities which exist in the system and which adversely affect the signal during transmission through the system.At the receiving end of the radio system, the receiver output contains a signal comprising the pilot frequency and a superimposed amplitude modulated signal, and this signal is applied to a product detector. The output of the product detector is a pulsating DC signal comprising a basic DC component, which is representative of the amplitude of the pilot frequency, and an AC component, which is representative of the system non-linearity. The pulsating DC signal is applied to one terminal of a capacitor.

Abstract: The baseband input to a frequency modulation transmitter is switchably connectable to a square wave generator, the amplitude of the square wave output being adjusted to provide a predetermined deviation of the FM radio transmitter. The output frequency of a pilot oscillator is also applied to the baseband input and it is subjected to phase modulation because of group delay which exists in the system and which adversely affects the signal during transmission through the system.At the receiving end of the radio system, the receiver output obtains the pilot signal which has been phase modulated by the group delay slope in the system, because of the square wave test signal. This phase modulation is detected in a phase lock loop, amplified, rectified and applied to a meter so as to provide an indication of the group delay slope in the system.