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

Sat Dec 29 16:13:19 UTC 2007

My 2 cents....

At what freq offset are the measurments being made?
(NLTL vs. SRD)

Is it that the SRD has more flicker noise and thus
is worse than 20log(n) for close-in noise? Or does
the SRD have a wideband noise floor that is worse
than 20log(n)?

-Brian, WA1ZMS

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Mike Feher
Sent: Saturday, December 29, 2007 9:53 AM
To: richard at karlquist.com; 'Discussion of precise time and frequency
measurement'
Subject: Re: [time-nuts] NLTL comb generators going away...

Over 20 years ago I was the lead guy in the development of the SCOTT Milstar
satellite terminal at Magnavox. Our uplink frequency was from 43.5 to 45.5
GHz. The PN specifications were essentially almost impossible to meet. The
terminal had it's own specification and used a Rubidium followed by a 100 Hz
crystal filter. Narrow filtering was used after all multipliers and a lot of
heterodyning was used in place of multipliers to come up with the 11 GHz
required for the PA. The PA was subcontracted out to two different
manufacturers due to the risks involved and they were each given 1 dB above
what would have been generated within the PA's X4 multiplier in PN increase.
So, instead of 12 dB they were allowed 13 dB of degradation. The multiplier
used was a dual stage varactor type multiplier, where the first stage would
get it up to 22 GHz and the second to the final frequency of the nominal 44
GHz. None of the amplifiers exhibited more than 12 dB of PN increase. In
fact, they all measured 12 dB. Admittedly, back then, this was not an easy
measurement to make. This was with 2 different manufacturers and I went to
both on numerous occasions, one on the east coast and one on the west. So,
this is why I wonder why an SRD would be that much worse. What is happening
that I am not aware of? Where is this extra residual noise coming from?
Thanks - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Rick Karlquist
Sent: Friday, December 28, 2007 9:00 PM
To: Discussion of precise time and frequency measurement
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] NLTL comb generators going away...

You need a really clean driver to be good enough to need a NLTL
instead of an SRD.  Whatever the intrinsic noise of the NLTL is,
it is lower than any practical source so you can consider it zero.

Rick Karlquist N6RK

John Miles wrote:
> 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
>>
>
>
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