By Richard F Schneider
Measuring frequencies from low
AUDIO all the way to microwave has always required many different counters or counter plugins, a good deal of range switching and cable changing, and at least — 7 dBm [100 mV) of signal.
Not any more. The new Model 5340A Microwave Frequency Counter [Fig. 1) measures frequencies between 10 Hz and 18 GHz using only a single input connector. Measurements are completely automatic, and sensitivity is —30 dBm (7 mV) from 10 Hz to 500 MHz, -35 dBm [4 mV) from 500 MHz to 10 GHz, and -25 dBm [12 mV) from 10 GHz to 18 GHz. Thus measurements may be made where signals are inherently low-level, or where directional couplers or lossy elements reduce the original signal level.
A typical sensitivity curve is shown in Fig. 2. Note that the counter is usable well above 18 GHz and that conservative specifications apply.
Model 5340A gets its high sensitivity and wide bandwidth from the new thin-film samplers used in its front end as harmonic mixers [see article, page 10). A new phase-locked loop design provides not only automatic operation, but also greatly reduced sensitivity to spurious input signals, harmonically related or not. Frequencies from 10 Hz to 250 MHz are counted directly, and frequencies above 250 MHz are measured using an automatic transfer oscillator technique.
Model 5340A is compatible with the new HP bus interface system.1 The bus system provides for control and communication between instruments up to 51 feet apart. As many as 15 devices can operate on the bus, so the 5340A can be part of an easily implemented automatic measurement system.
Equipped with all of its systems options, Model 5340A can communicate digitally with printers, calculators, card readers, computers, teleprinters, and other devices. All of its front-panel controls [except power on/off) may be remotely programmed, including resolution, range, reset, and sample mode.
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