sampler output waveform during zero beat tuning in the Pulsed RF mode.
a. General. When the Model 5345A Function switch is positioned at PLUG
IN, the counter's accessory connector plug is activated and the counter
receives its input signal from the Transfer Oscillator. Also the counter's
gate time control is taken over by the Model 5257A, but the setting of the
counter's Time Base determines frequency resolution.
A Time Base of 1 ms
provides 1 kHz resolution, the 1 count of the last digit in the display.
This time base is generally suitable for the whole frequency range from .05
to 18 GHz. In the microwave range where this degree of resolution is not
required, a 0.1 ms time base will shorten counting time and give a 10 kHz
resolution. Likewise, on lower frequencies the time base can be lengthened
for the maximum resolution the counter readout allows.
b. Input Voltages. The maximum input voltage must not be exceeded to
prevent diode damage in the sampler. Peak voltage is the critical quantity
rather than average or rms values. Know the signal voltage before applying
it to the input jack. Use attenuators as a precautionary measure where the
input voltage is questionable.
Extra care should be taken with pulsed
signals since short voltage spikes can be just as damaging as steady state
values. The maximum permissible input voltage is 2 volts peak-to-peak (+10
dBm) for a CW carrier.
A minimum input amplitude is specified to assure proper instrument
operation, even though it may respond to lower amplitudes.
sensitivity levels were stated in para 1a.
c. Calculation of N. For frequency ranges above .2 GHz, if the input
signal frequency is known to within the sampling frequency (from 66.7 to
133.3 MHz), the harmonic number N can be found directly.
In this case,
estimated input frequency (fx) is divided by sampling frequency (fs) as read
on the counter with the thumbwheels set at 001. The answer is N: fx/fs = N,
where fs equals VFO frequency (fv).
In the .05 to .2 GHz range, fs is fv prescaled by four. The counter
reads fs, not fv.
Therefore, for direct calculation of N, the estimated
input signal frequency should be known to within the sampling frequency
(from 16.3 to 33.3 MHz). Hence the procedure is the same as described in
the preceding paragraph.
The counter reading (fs) is divided into the
estimated input frequency and the answer is N: fx/fs = N, where fs equals fv
divided by 4.
The frequency measurement procedure using direct calculation of N is
as follows: set the thumbwheels at 001.
Tune Frequency MHz for an
indication of zero beat or phase lock, observing Level Adj and Mode