Figure 1.
Model 5257A transfer oscillator.
The input sensitivity of the plug-in is 100 mV rms (-7 dBm) for input
frequencies of 50 MHz to 15 GHz and 140 mV rms (-4 dBm) for input
frequencies of 15 to 18 GHz.
A nominal input impedance of 50 ohms is
featured for all measurements. The meter indicates loop phase error under
locked conditions for the PC mode and functions as a zero beat indicator for
the Pulsed RF mode.
The Pulsed RF Out BNC connector provides a 0.5 volt
peak-to-peak signal for an external oscilloscope.
The instrument uses a wideband sampler to compare the input signal
waveform with the internal VFO.
This eliminates the need for a harmonic
generator following the VFO and requires far less power than other methods.
In operation, the VFO is tuned to a subharmonic of the input signal to
produce a do voltage at the sampler output when the input and internal
waveforms are coincident each time the sampling gate opens. The automatic
phase control circuit operates from this dc voltage.
The circuitry has a
wide capture range and it is only necessary to tune through the proper
frequency and the VFO will "lock in."
Therefore, tuning is rapid and
uncritical. If the lock is lost due to an intermittent signal, the Model
5257A will automatically relock when the signal again appears.
As previously mentioned, the Pulsed RF Out jack on the front panel,
connected to the sampler output circuitry, permits use of the Model 5257A
for down conversion to extend the range of low frequency instruments such as
oscilloscopes, FM discriminators, etc. Also, an oscilloscope can be
60
Previous Page
