HP8648 information request

[tkamiya]

I have HP8644A and B, so I'm pretty familiar with these. 

I have been looking at HP8647 and HP8648 series but few things aren't clear.  I wonder if someone who owns these can help me out.

I found a pretty nice comparison here, which answered a lot of my questions already.
http://www.libertytest.com/assetmanager/uploaded/pdf-201031-145924-hp_864x.pdf

What it doesn't mention are:

These models come with LCD and FD display.  Yet, they don't appear as options.  Did they start with one type and switch to the other?

How are these models different from HP8644 series besides the obvious?  (size and weight)  These all come from the same time period.  Are these good, better, best kind of difference?  If so, where are these models positioned in HP's line up?

Before anyone asks, I want these because of its size and weight.  I always hurt myself trying to move what I have.  So lighter is an advantage. 

[nfmax]

These instruments started out with LCD displays and were modified to use VFDs towards the end of the 'HP' era. I have an HP 8647A with LCD display, and an Agilent 8648D with VFD display.

They are low cost, basic signal generators. The signal purity (phase noise, residual FM) is not very good, though the 8648 is significantly better, and they exhibit wideband noise on the output. They are best suited to 'in channel' measurements and tasks such as receiver alignment and fault-finding. Also useful for EMC susceptibility testing.

Notoriously, the higher-frequency C & D versions of the 8648 allow you to set an output level above what the instrument can actually deliver above about 2.5 GHz, but do not provide a warning that this is happening.

[tkamiya]

Thank you.

Then I'll look for 8648B with VFD, and spend accordingly....  For some reasons, they typically go for as much as and higher than 8644.  Every now and then, I see bargains.  It would be a good unit for my test bench.

Thanks again for your reply.