[G0HZU_JMR]

The classic old HP8566/8 analysers did all the crystal filtering up at 21.4MHz and this includes the 10Hz RBW filter. Because of the ropey nature of the narrowest crystal filters in the 8566/8 (drift and poor amplitude response up at 21.4MHz) the next generation of analysers (eg HP8560A) only attempted to do crystal filtering down to 300Hz RBW. This was done at the third IF at 10.7MHz.

For RBW below this, the narrowest RBW filters were done in the digital domain. This improved the performance and consistency a LOT. The later HP 8560E and 8563E supported a 1Hz RBW filter in the digital domain.

It's several years now since I last used an HP8560 or 8563 in either the A or E versions. At work, these analysers have mostly been sold or scrapped. At one time there were dozens of them, and I used them on a daily basis. I can remember when the first HP8560A arrived at work and this must have been in the early 1990s. I spotted a dead 26GHz HP 8563EC sat sulking under a bench at work last week. It has a sweep fault and I suspect it will go in the WEEE skip soon. I think it is the last one left in the engineering labs.