Model 8640B TM 9-4935-601-14-7&P
PERFORMANCE TESTS
4-25. OUTPUT LEVEL FLATNESS TEST (Cont'd)
2. Adjust OUTPUT LEVEL vernier for a power meter reading of +3 dBm at 50 MHz. Using RANGE and
FREQUENCY TUNE controls, slowly tune -Signal Generator from 512 MHz to 0.5 MHz. On each range, note
maximum and minimum power meter readings in dBm.
3. The overall maximum reading and the overall minimum reading should both be within 0.5 dB of the reading at 50
MHz.
_________________0.5 dB
4-26. OUTPUT IMPEDANCE TEST (In Band)
SPECIFICATION:
Impedance: 50Ω ac coupled, 40 Vdc maximum, VSWR <2.0 on 2V and 1V output ranges; <1.3 on all other ranges.
DESCRIPTION:
The generator's output signal is reflected back into the RF OUTPUT jack by a coaxial short at the end of an adjustable
stub (a variable length of air-line). This reflected signal is re-reflected by any mismatch at the jack. The re-reflected
signal combines with the output signal according to the relative phase and magnitude of the two signals. The combined
signal is monitored by a directional coupler and then measured by a voltmeter. Maximum and minimum power levels are
noted as the electrical length of the stub is varied (i.e., the distance from the RF OUTPUT jack to the coaxial short is
varied). VSWR is then calculated from the formula
Vmax
VSWR =
Vmin
4-37
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