HP8551B with the 5th harmonic of a 500MHz signal displayed at 2.5GHz
The top unit is valve-less, using transistors
The bottom unit is a "plumber's delight" handling the 10MHz to 42GHz specification
I suspect the lower limit may be a lot less as the dials imply that it beats a 2GHz oscillator with a VFO, tuning down to 2GHz
My Marconi sig genny has a similar arrangement which lets you generate zero Hz (is that meaningful?) when the dial is set to "0"!
Picture of the front of a Type 608E.
These types of VHF generators are not much use in a domestic repair
workshop as they do not include FM. I suppose they would be more
useful for overhauling aircraft equipment as they
still use VHF-AM.
This monster, weighing in at around 100lbs covers 10-480MHz.
These equipments were made in the days before clever methods of frequency stabilisation had been invented and relied on mechanical ruggedness (=weight) to ensure that the output frequency was stable. Another requirement of these things, with their very accurate output attenuators (the dial on the bottom right), was not to leak any RF which might upset measurements.
Even with professional test equipment, RF leakage can pose problems. I was once servicing a marine VHF transceiver and was checking the distress frequency calibration, when the local Coast Guard popped up and complained about my test signal on his receiver. This despite the use of screened leads and a dummy load.
