c. Controls and Connectors.
Throughout the following
description, refer back to figure 1 as becomes necessary.
(1) Input Connector. Signal input impedance is 50 ohms nominal for
connection to an unknown frequency source. The connector is a precision "N"
type female connector.
(2) Frequency MHz Control. This dial reads the VFO frequency. For
convenience however, the counter readout provides the sampling frequency
measurement used for calculations. The dial reading is not to be used for
calculations. Concentric knobs on this dial provide coarse and fine tuning.
In the Pulsed RF mode, the meter reads the relative
amplitude of the difference frequency (beat) between the VFO harmonic and
the input signal. At nine-tenths of full scale a red division line marks
the APC Mode, the meter monitors phase error of the phase-lock loop. Zero
phase error deflection is nominally at mid-scale. When out of phase lock,
in the APC Node, the meter reads the nominal mid-scale deflection. In phase
lock the meter reads above, below, or at the zero phase error deflection
depending upon phase error.
This red knob, concentric with the Range selector knob,
selects Pulsed RF and APC Modes.
(5) Thumbwheel Switches. The thumbwheels are set to harmonic numbers
N of the sampling frequency. They actuate switches which preset a counter
decade assembly in the Model 5257A to extend the counter gate in increments
of units, tens and hundreds.
At a setting of 001 the counter reads the
sampling frequency (N = 1).
wide variations in input signal levels and the wide frequency range of the
instrument. Initially, the Level Adj is turned fully counterclockwise and,
after tuning to zero beat, it is turned clockwise until the meter reads at
the red division line.
(7) Range. Range is selected with the black knob which is concentric
with the Mode switch knob. It includes four ranges: .05 - .2 GHz, .2 - 1
GHz, 1 - 4 GHz, and 4 - 18 GHz. This switch compensates the phase lock loop
for the wide frequency range of the instrument. It also selects a gate time
extension factor for the counter: the scale is 1N in the .05 to .2 GHz range
and 4N in the higher ranges.
(8) Pulsed RF Out.
This BNC connector goes to the sampler output
such as down conversion to extend the frequency range of low