[time-nuts] 35601A as stand-in for 11848A ?
seiskent at earthlink.net
Fri Jan 11 03:41:47 EST 2008
I bought a 35601A hoping to use it for phase noise measurements but
discovered that the only way to control the unit is through the HPIB
interface, presumably using the 3047A software which I was never able to
Looking inside the 35601A, you find rather involved signal routing with
dozens of mechanical and FET switches for routing the various signals
around. To complicate matters, the control lines from the 12 8-bit registers
that actuate the switches seem to follow no discernable logic with many
appearing to be assigned randomly. There must have been some software
compatibility issue with previous equipment. The 11848A shares many of the
same control signal assignments but there are enough differences both in the
control signal assignments and other circuits to make the 3048A software
unusable with one possible exception.
There are two main parts to the 35601A and the 11848A units, the High
Frequency circuits and the Analyzer Interface. The High Frequency circuits
which contain the input mixers, input switching, diplexers following the
mixers, amplifier chain, gain switching, PLL lead-lag filters and other PLL
circuitry are almost identical. What is different is the Analyzer
Interface, assembly A4. The 35601A was closely tied to the 3585A spectrum
analyzer, using the 350Khz IF out of the analyzer in the low frequency
processing circuits. Although the 11848A also uses the 3585A for the
offsets greater than 100Khz, it doesn't rely on the 350Khz IF output of the
3585A. They also changed the LP/HP filter arrangement and signal path
switching in the Analyzer Interface of the 11848A which means that the 3048A
software will not correctly control the Analyzer Interface and so will not
properly drive a 3561A spectrum analyzer. So, the bottom line is the 3048A
software won't fully work with the 35601A.
Now for the possible exception. There is a facility in the 3048A software
which allows manual control of the 11848A. Since the 35601A High Frequency
circuit (A4) is essentially the same as the 35601A High Frequency circuit,
you might (I haven't tried it) be able to use the 3048A software to manually
control the High Frequency board in 35601A. Doing this you can manually
change the PLL gain and filtering to establish lock. Of course, you really
wouldn't be able to use any of the features of the 3048A software that make
it so useful.
I also recently acquired a 11848A interface and have written a small
program to control the 11848A (and also the 35601A) over the HPIB bus which
allows the various signal paths and filters to be manipulated using a PC. My
eventual goal, largely inspired by John Miles Phase Noise program (thanks
for contributing this great program), is to emulate some subset of the
functionality of the 3047A/3048A software. It turns out, there are quite a
few "details" to be concerned with but John has already done much of the
heavy lifting in controlling various spectrum analyzers and slogging through
some of the more problematic noise computations, which makes the task more
As you may know, the 11848A Service Manual is available on the Agilent
The diagrams and schematics are marginally readable, however they are clear
enough to get an idea of how the unit operates. The block diagram is hard to
read, but there is another one in the 3048A Phase Noise Measurement System
Reference Manual - 03048-90002 on pfd pages 296 through 299 (section 5-40)
that can be printed out and pasted together. Assembly A4 is the High
Frequency portion and, as I mentioned, closely matches the 35601A.
The 3048A Operating, Reference, and Calibration manuals are at:
By the way, this is my first post, although I have been following the
discussions here with fascination for quite awhile - like many others I
suspect. What at first was little more than a passing interest in time and
precise measurement, has now become a much more focused effort to measure
time, time intervals, phase noise, and frequency, aided and abetted by the
many interesting discussions on this list. Thanks to everyone for
contributing to this great resource.
----- Original Message -----
From: <BriMDavis at aol.com>
To: <time-nuts at febo.com>
Sent: Sunday, January 06, 2008 4:38 PM
Subject: [time-nuts] 35601A as stand-in for 11848A ?
> John Miles wrote:
>>> How many significant digits are there in a 5120A price quote?
>> $2.0*10^4, last I heard. :)
> OK, I'll be crossing that one off the home lab wish list!
>> 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.
> At this point, just the detailed 35601a system block diagram
> showing the switched signal paths and gain/filter settings
> should be enough for me to figure out how practical building
> a Franken-3048a would be.
> Don't spend time scanning the manual on my account, I'll
> order a hardcopy from Manuals Plus once I sort out why they
> have two different P/Ns listed for the service manual.
>> You either need a 3047A/3048A system, or some custom software
>> that you'll have to write yourself.
> The later discussions of homebrew PN setups may have
> obscured my original question:
> Has anyone ever looked into the feasibility
> of using a 35601a as a stand-in for the 11848a
> in a 3048a phase noise system?
> I have a 9000/340 computer with the 3048a software,
> a 35601a, and can probably pick up the 3561A narrowband
> analyzer needed by the 3048a software for $300-500 USD
> (with some patience).
> The 11848a's usually still have four digit price tags.
>> 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.
> Yes, I plan to have two (or three) copies of the LO/reference chain
> in question, and pull one of the OCXO's for quadrature lock.
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