[time-nuts] OT? - Irish Submariners

Don Collie donmer at woosh.co.nz
Sun Jan 6 02:16:35 EST 2008

Has anybody heard the one about the Irish Submariner who was previously a 
Mathematician?  He would add the number of times the sub decended to the 
number of times it had surfaced, and divide the total by two - if there was 
one left over, he didn`t open the hatch.
Cheers!...........................................Don C.

----- Original Message ----- 
From: "John Miles" <jmiles at pop.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Sunday, January 06, 2008 4:59 PM
Subject: Re: [time-nuts] 35601A as stand-in for 11848A ?

>> John Miles wrote:
>> >
>> >I have a 35601A, although I've never done anything with it.
>> >
>> Did you happen to spot any service/calibration manuals
>> for the 35601A? I haven't found anything online yet, but one
>> of the manual dealers I checked lists a hard copy.
> I do have a hardcopy manual for the 35601A but am not sure if I have a 
> .PDF
> of it or not.  Will check tomorrow and let you know.  I can probably scan 
> it
> easily enough if not, >11x17 foldouts excepted.
>>  I've never used the older 3047a, but the impression I have from the
>> catalog info I've found so far is that the 3048a updated to the newer
>> 3561a for narrowband analysis and added more internal sources
>> to the 11848a for convenience; I'm hoping that much of the basic
>> signal path for calibration and quadrature lock was left alone.
>> >
>> >The 11729B/C plus an 8662A (or even an 8640B) has everything most
>> > people will ever need for PN measurement.
>> >
>>  I need to measure things that are lower close in than the 11729/8662a
>> combo noise floor; i.e. OCXO, direct synthesis from OCXO, amp/divider
>> residual noise floors, down to 1-10 Hz offsets.
> Keep in mind, though, that without the 11848A's internal sources, you're
> going to have to supply some kind of reference source at the same 
> frequency
> as the DUT.  At that point, all the 35601A, 11848A, *or* 11729B/C is doing
> for you is providing a mixer, an LNA, and a quadrature-locking PLL in one
> box.  They can all be used to compare two external sources directly if you
> want, with no 8662A required.
> Of those models, only the 11729B/C is really meant for standalone use
> (meaning, without a GPIB controller.)  The 35601A doesn't have buttons on
> the front panel to let you change PLL bandwidths, override the default 
> loop
> capture range, or anything else, and I don't believe the 11848A does,
> either.  You either need a 3047A/3048A system, or some custom software 
> that
> you'll have to write yourself.
> I can't speak from experience, but I don't know of any magical reason why
> the 35601A's or 11848A's noise floor will be much lower than the 11729's.
> See http://www.ke5fx.com/regen.htm for a case where the 11729C goes up
> against the TSC-5120A in a low-noise measurement scenario and gives a
> reasonable accounting of itself.  If the 11848A has an advantage, it
> probably comes at offsets < 1 kHz, where the 11729C doesn't do so well.
> Note that HP is careless with the 11729's noise-floor specs in some 
> places,
> in that they report what is really the system noise floor, limited by the
> 8662A they assume (hope) you are using.
> One caveat: to use the 11729 to measure carriers below about 20 MHz, you
> *will* have to add an LPF prior to its LNA.  Otherwise the upper sideband
> from the phase-detector mixer will enter the LNA and saturate it.  Not the
> end of the world, but the additional LPF wouldn't be necessary with the
> 11848A, and I assume not with the 35601A either, because they have more
> internal filter options.  (Which, again, have to be selected via GPIB.)
> Analyzer-wise, the fact that you need to look at offsets down to 1 Hz is a
> complication.  You cannot use a conventional spectrum analyzer for that
> unless you have a new/fancy model with sub-1 Hz resolution.  An FFT 
> analyzer
> would be needed, and like Bruce suggests, a sound card may be the best way
> to go there.  (I don't currently support sound-card input in my
> noise-measurement app, but I probably ought to.  If someone needed that
> capability and wanted to help test it, it wouldn't be out of the 
> question.)
>> >Renting/buying a E5052A or TSC5120A does get to  be expensive
>> >
>> How many significant digits are there in a 5120A price quote?
> $2.0*10^4, last I heard. :)
> -- john, KE5FX
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