For example: Agilent E4440A or Anritsu 68369
Racal Instruments Counters/Timers
Racal Instruments 407494-011
2251A, 200 MHz Univ. Ctr./Tmr. w/Int. Precision
Manufacturer: Racal Instruments
Racal Instruments R-2461-Cd
2461-Cd, 200MHz ,2-Ch UCT w/o Int.Frequency Std.
Manufacturer: Racal Instruments