Wide band a.c. measuring instrument employing a wobbled heterodyning circuit to convert high input frequencies to measurable lower frequencies

Claim 1

A MEASURING INSTRUMENT COMPRISING AN A.C. VOLTMETER, A BAND-PASS A.C. AMPLIFIER HAVING AN OUTPUT OPERATIVELY COUPLED TO SAID VOLTMETER, SAID AMPLIFIER EXHIBITING A SUBSTANTIALLY FLAT FREQUENCY RESPONSE CHARACTERISTIC OVER AN OPERATING REGION HAVING A PREDETERMINED FIRST AND RELATIVELY LOW CUT-OFF FREQUENCY AND A PREDETERMINED SECOND AND RELATIVELY HIGH CUT-OFF FREQUENCY, INPUT MEANS FOR APPLYING AN ALTERNATING CURRENT VOLTAGE TO BE MEASURED TO SAID INSTRUMENT, FREQUENCY CONVERTER MEANS HAVING AN INPUT COUPLED TO SAID INPUT MEANS, HETERODYNING OSCILLATOR MEANS OPERABLY ASSOCIATED WITH SAID CONVETER MEANS, SAID OSCILLATOR MEANS INCLUDING ADJUSTABLE FREQUENCY CONTROL MEANS TO CONVERT AN INPUT VOLTAGE HAVING A FREQUENCY ABOVE SAID OPERATING REGION TO A BEAT FREQUENCY OUTPUT VOLTAGE HAVING A FREQUENCY WITHIN SAID OPERATING REGION, MEANS COUPLING SAID OUTPUT VOLTAGE FROM THE OUTPUT OF SAID CONVERTER MEANS TO THE INPUT OF SAID AMPLIFIER, AND MEANS FOR PERIODICALLY VARYING THE BEAT FREQUENCY OUTPUT OF SAID CONVERTER MEANS WITHIN A DEVIATION RANGE SUBSTANTIALLY GREATER THAN TWICE THE RANGE BETWEEN ZERO AND SAID FIRST CUT-OFF FREQUENCY, THE RESPONSE TIME CONSTANT OF SAID VOLTMETER BEING LARGE COMPARED WITH THE PERIOD OF SAID FREQUENCY VARIATION.