Repairing a Hewlett-Packard 5245L Frequency Counter, Part 4—Onward to 3 GHz

The Hewlett-Packard 5245L digital frequency counter, when introduced in 1963, handled a top frequency of 50 MHz, but it had a plug-in slot to accommodate the future. Only a year later, along came the 5254A plug-in, which raised the top frequency to 3 gigahertz (gHz), sixty times the original limit, plenty to handle the microwave communications to and from the Apollo spacecraft en route to the Moon, which it did in numerous installations in NASA ground stations. Time has taken its toll on the intricate and delicate mechanisms required to manipulate such frequencies. What’s needed to get it running again?

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