I needed a signal generator with good phase noise performance but with tolerable construction complexity, and reasonable size and weight. I looked closely at the IFR/Marconi range mentioned by Dave (G4AON, above) and would have been quite happy to own one of the models he mentions. However, other excellent performers, with slightly better phase noise, are the Rohde and Schwarz SML series and I was fortunate enough to find a pristine, ex military contractor, SML-01 with the pulse modulator and reverse power protection options fitted for AUD 800 (USD 560). Here's a data sheet:
https://www.testequipmenthq.com/datasheets/Rohde-Schwarz-SML01-Datasheet.pdfOne good feature is the fast and accurate electronic attenuator; stepped "sweep" functions are often less useful in ham environments than they appear by the time switching and settling specifications are accounted for but, with the fast frequency step and the electronic attenuator, I've found the SML-01 to be much more useful than e.g. a Rigol DSG815. Like the Marconi generators the SML range also allows a "divider only" mode (pioneered by the HP8640B), which gives excellent phase noise over a very useful part of the frequency coverage. Overall, the R&S unit shows a clean pair of heels to the old HP in overall phase noise terms. (Still not as good as some of the later behemoth HP generators, which are fine instruments but weighty and not known for their reliability as they age).
One thing I liked about the IFR/Marconi generators is that more of the service information (to component level schematics) is in the public domain. However, I judged that there was just about enough SML information around to make the trade-off between serviceability and phase noise swing towards the SML. If you look at the failure points of the better HP and similar generators, mechanical attenuators are prominent, so well-designed electronic replacements are desirable. (Bear in mind we are comparing low-GHz generators here; all bets are off if you decide you want a mm-wave synthesizer)!
73, Peter.