Ael Microtel, Ltd.

Larry Y Onotera

Abram Froese

Alvin Liebelt

Leonard Dueckman

Muhammad J Ahmed

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.

Apparatus for testing microwave radios having 35 MHz if using test

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. The AC component appears at the other terminal and is rectified and integrated to obtain a DC signal, the amplitude of which is proportional to the slope component in the system non-linearity. This DC signal is measured by a direct current meter.

Built-in linearity testing arrangement for an FM radio system

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.

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Surrey, Canada

Larry Y Onotera