signal generator recommendation

[cncjerry]

I have an HP 8648C which goes up to 3.2Ghz, synthesized, some modulation, etc.  Haven't had it long, maybe 6 months, got a great deal on it.  It has the high stability time base, option 1E5.  The phase noise isn't bad, but isn't great.  Here's the question, what would be the next step up, maybe two steps up in synthesized generators?  I prefer HP but am open to other brands.  I figure I can get $600 for the 8648C, maybe a little more.   So if you have a recommendation, assuming I sold the 8648, how much more would I have to spend?  3.2Ghz meets my current needs but I would like to get to 6G but I could use a doubler.  I've been scanning eBay, see 8664s, etc.  I don't know anything about the Marconi generators but I read good reports on them.

Thanks

[memset]

You can try used R&S SML02-SML03. Slightly better phase noise, optional OCXO. Can be found for <$1000.
Speaking of current analog generators, R&S SMA100A + SMA-B22 option for very good purity and exceptional phase noise. Price tag is sky-high.

[G0HZU]

IMO the best 'general purpose' sig gen (in terms of bang per buck and readily available) is the 4GHz HP/Agilent ESGD E4433B. This is the version of this sig gen that supports IQ modulation. I'd recommend getting one with the internal dual arb generator option UND. I have two of them and I bought one for £800 about two years ago and another one a year later for about £1000. If you are patient you can get these generators for this price although some sellers will still want double this amount or more.

However, it does have a few shortcomings...
The phase noise performance is fairly average when used above 1GHz. However, because of the frequency plan it uses (and the need to support the IQ modulator) the performance in terms of phase noise is very poor when used down on the HF bands for example. It's only going to be slightly better than the HP8648 in terms of phase noise down here and way, way off the phase noise performance of the best generators on the HF bands (2-30MHz).

The internal AM/FM/PM modulation system it uses is pretty good but it isn't in the same class as a decent Marconi generator from the 1990s in terms of mod accuracy or mod linearity.

But the good things about this sig gen still make it a very powerful tool if you can live with the phase noise etc.

The levelling/accuracy performance is extremely good across the whole 4GHz range.

It has a very versatile IQ modulator with fairly wide bandwidth.  One of the best generators I've ever used in this respect.
You also get a fairly good LF output port with a built in function generator. This can produce various LF waveforms including sine, square, triangle ramp, noise etc and this can be very useful. But if you get the arb generator option UND you can program it with all kinds of custom modulation types and there is a useful library of modern digital modulation types built in.

IMO sig gens are a bit like shoes. You can never have too many of them and I have about a dozen RF sig gens/sources here and each of them is good at 'something' that the others can't match. One is never enough!

[cncjerry]

G0, thanks. I thought about putting I/Q in my post as a 'want' so I appreciate the pointer.  I see there are 4422 generators as well.  Are there lower priced models that can be hacked up to the 4433?

I have to look at the specs on my 8648C again and see if it has a problem.  It just seems to have more spurs and noise than I thought it would when purchased.  Granted I got if for a good deal but the SFDR just isn't good enough.  I do like the dual dials for feq and amp as well as the UI seems fast.  I'm going to post a picture of my 8648C output over in the yahoo HP group to see what others think.  Maybe I just have to fix it.

[Wuerstchenhund]

IMO the best 'general purpose' sig gen (in terms of bang per buck and readily available) is the 4GHz HP/Agilent ESGD E4433B. This is the version of this sig gen that supports IQ modulation. I'd recommend getting one with the internal dual arb generator option UND. I have two of them and I bought one for £800 about two years ago and another one a year later for about £1000. If you are patient you can get these generators for this price although some sellers will still want double this amount or more.

A possible alternative to the Agilent E4433B is the Anritsu MG3700A. Available in 3GHz and 6Ghz variants, it offers better RF performance than the old ESG-D, and it's dual channel Arbs (up to 120MHz BW) come with up to 2GW/1Gpts (1GW/512Mpts per ch) of memory as option (the Agilent ESG-D UND only has 1Mpts/ch, and are only good for 35MHz BW or so). It's also newer than the ESG-D, with a large color display with nice UI, and its Windows software (IQproducer) is still actively maintained as it's used for other Anritsu generators.

The MG3700A does lack direct AM/FM modulation, though, but it does offer pulse modulation.

The 3GHz variant can occasionally be found below the $1k mark (I've seen them for less than $800 on occasion) but the 6GHz variant is generally pretty expensive and also still rare.