Analysis of errors in internal marker-pair generation of sweep generators

Two configurations of pulse-type marker-pair generation in sweep generators are analysed to explain the causes of frequency errors in its internal marker-pair. One configuration employs amplitude modulation of the swept frequency oscillator for producing markers whereas the other uses a marker adder circuit after video detector of the unit under test. It is shown that main contribution to the frequency error is not only due to long term drift in tuned amplifiers of the pulse-pair generator circuits but also due to the delay in producing the pulse-pair. It is further shown that the error due to the drift in tuned amplifiers is not compensatable by simple known techniques but the error due to the delay of pulse-pair generator is compensatable to a certain extent by delay of the unit under test for the latter configuration holds good only till the delay of unit under test is not more than twice the delay of pulse-pair generator circuits. Lastly experimental results about the marker-pair accuracy are discussed and comparative advantages of both the sweep generator configurations are given.