The "olden" days
In the 1960's, they didn't have all the PLL circuits (well, save for the old AN/URC-32 transceiver used by the U.S. Navy) and digital chips (ICs had yet to be invented) to do things like this. They used traditional "radio" methods of doing this. Beginning with a crystal-controlled oscillator, they would feed the signal to an amplifier operating in a non-linear mode which would generate several harmonics, such as X2 or X5. The output of this circuit was fed to a tank circuit tuned to the harmonic needed. For instance, they might start with a 1MHz standard frequency and double this to 2MHz. Then they'd feed that 2MHz to another such circuit to get a fifth harmonic, 10MHz. That one might go to another doubling circuit to get 20-MHz and finally that output to a quintupler to get 100MHz. If they needed clean sine waves, they'd always send those signals through one or two more tank circuits tuned to the desired frequency. The AN/USM-207 frequency counter multiplied 1MHz up to 100MHz for use in the gating circuit in this way. These circuits were known as frequency multipliers (frequency doublers, frequency triplers, etc.) and were very common in communications equipment. It was a wonder way to get clean sine wave signals with the same precision as the original reference frequency.
Dean