[R-390] HP-8640B vs. HP-8654A/8655A/11710B

[2002tii]

Barry wrote:

>Anyone on the list have any experience with an HP8654A/8655A/11710B 
>combination?  The reason I ask is I have an 8654A/8655A and am 
>thinking of getting the 11710B to get the lower parts of the HF 
>range and was wondering if I'd be better off with this or getting an 8640B.

Well, the 8654 (A or B) was never intended to be an 8640B-class 
generator.  In terms of signal purity, it may be the dirtiest RF 
generator HP ever made, including the earliest synthesized 
models.  Fine for basic alignment, but not really useful for 
twin-tone IM measurements or anything fancier.

These days, one would typically use it with a counter -- but be 
careful, the auxiliary output on the rear panel is not well isolated, 
and any crap that comes out the counter's input (not at all unusual) 
can end up on the main output, further compromising signal purity.  I 
suggest using a 20 dB pad between the rear panel output and any 
counter to minimize this.

The 11710B works reasonably well (I use them with 8640Bs to get below 
400 kHz), but the internal crystal oscillators are a bit noisy so the 
mixed output has a poorer noise floor than the 8640B and also has 
more phase noise, if you are doing anything where phase noise is a concern.

As Al noted, the "B" version makes a voltage control input available 
on the back panel.  If you have the HP 8655A reference/phase detector 
(or build something similar -- the originals were rare even in their 
own day), you can use this input to lock the 8654B to an external 
standard, at the price of quantized frequency steps.

Best regards,

Don