[time-nuts] NLTL comb generators going away...

[John Miles]

It's hard to read the tea leaves on that.  Dieter Scherer has one note
(Generation of Low PN Microwave Signals) that shows the 33004A multiplier's
output noise at -140 dBc/Hz to -148 dBc/Hz from 1 to 10 kHz, at 5.5 GHz
(N=11).  If that is the case with the 11729's multiplier, then the NLTL part
is not really necessary even with an upgraded 640 MHz reference chain.  But
then, something else must be responsible for the 11729's residual PN spec,
and I don't see what that would be.

Of course, I'd assume that PSPL's measurements were taken with the crappiest
SRD part they could find. :)

It appears that the 11729's 640-MHz PA can drive the 7123 adequately,
although the 12.16 GHz comb line is somewhat close to the spec limit of -20
dBm.  The 7113-110 is a better replacement for the 33004A in the 11729C,
since it would actually be operating in spec.  They have several of those in
stock (I just ordered 2 of the 8 they had left).

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of Richard (Rick) Karlquist
> Sent: Friday, December 28, 2007 10:08 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] NLTL comb generators going away...
>
>
> The SRD (step recovery diode) definitely degrades the phase
> noise beyond 20 LOG N, according to Agilent engineers I have
> talked to.  They mentioned a number like -150 dBc/Hz or something.
> Having said that, you also have to be very careful to design
> the driver (especially with NLTL) or it will become the limiting
> factor.
>
> Rick Karlquist N6RK
>