Four Designs Company | 24 Aug 18:04 2015

Re: Wavetek 4912

Sorry, the 4912 has been sold.

Bob Koller
Four Designs Company
20615 NE 22nd Ave
Ridgefield, WA 98642

On 8/24/2015 9:00 AM, volt-nuts-request@... wrote:
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> Today's Topics:
>     1. Voltage Modified Allan Variance (Poul-Henning Kamp)
>     2. Re: Voltage Modified Allan Variance (Andreas Jahn)
>     3. Re: High Resolution DAC (Sam Reaves)
>     4. Re: Wavetek 4912 For Sale (Charles Black)
(Continue reading)

Sam Reaves | 24 Aug 05:27 2015

Re: High Resolution DAC

Have a look at this article by the late and great Jim Williams:

Is 20 bits good enough for ya?

Poul-Henning Kamp | 23 Aug 20:18 2015

Voltage Modified Allan Variance

I have come clean:

Sometimes I run voltages through the Modified Allan Variance, and
it turns out to be very informative.

Please, somebody with more time than me, take this idea and run
with it...


Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@...         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Four Designs Company | 21 Aug 22:42 2015

Wavetek 4912 SOLD

SOLD, thank you!


Four Designs Company | 21 Aug 21:44 2015

Wavetek 4912 For Sale

I have an inoperative 4912 DC Standard for sale. The batteries are 
completely dead, and will need to be replaced. I have powered it up with 
the battery pack disconnected, but cannot get an output from the front 
panel jacks. I am not sure if it would normally output without good 
Decent condition, pictures on request.
So, this is offered AS-IS. $300 plus shipping, CONUS only due to the 
size and weight.



LCR meter calibration certificate

I just got my LCR meter back from Keysight today.

For anyone interested in looking at the cal certificate, which includes the
uncertainties, a copy may be found here,

It's not entirely sure if it was adjusted or not, as the instrument was
upgraded, although I'm not convinced that the upgrade really would have
required any adjustments. I suspect only a verification it was working, as
it was purely a software upgrade. Though perhaps it allows other hardware
in the meter to be used.

It lists

As received condition: "Not applicable, as this calibration certificate
applies to the initial calibration of a new, refurbished or upgraded
Action taken: "The equipment was upgraded."

So nothing specifically mentioned about it being adjusted, but nothing to
indicate if it was in spec when received either.

There's a few things rather puzzling about this.

1) Why did Keysight use two 3458A multimeters to calibrate it?

2) Why did Keysight use two 53132A frequency counters to calibrate it?

3) It's not clear to me what the actual values of the devices they used to
(Continue reading)

Mark Sims | 20 Aug 02:31 2015

Anyone know how to make stable inductors?

It's a lot harder than making stable capacitors...  particularly for low inductance values.  I think the
process involves the use of rainbow flavored unicorn tears.  There are some 0.01% standard inductors on
Ebay starting at around $400 each.  Also some .1% ones for a lot less.  Decent L measurements are a cesspit of
traps and gotchas...  things like L shifts with current, frequency, moon phase are just the start. 		 	   		  

Anyone know how to make stable inductors?

I was looking to make some inductors that I can use as a sanity check for
my HP 4284A LCR meter. I don't too much care what their values are, but I
want them to be stable with time. Any suggestions about the best way to
make or buy them? I'd like values in the range of 1 nH to 100 mH.

The LCR meter has 4 terminal Kelvin connections, with 4 x BNC sockets on a
22 mm pitch.

The meter is at Keysight at the moment being calibrated, along with a free
software upgrade they are kindly providing. So I'd like to measure some
inductors when it comes back, and track their values over time, to see if
the meter is drifting.

The meter covers 20 Hz to 1 MHz, and has a basic uncertainty of 0.05%, so
ideally I'd like to keep inductor changes to less than 0.005% over a year,
so the inductor is an order of magnitude better than the meter. Maybe that
is not practical. As I say, the absolute value is not important, since I
only want a comparison.

The calibration costs on this meter are not too bad (£207 GBP), but the
calibration interval is 6 months, which is a bit annoying. I'd rather not
be sending it off every 6 months if I can satisfy to myself it has not
drifted too much. Luckily I don't need to satisfy anyone else.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
Registered in England and Wales, company number 08914892.
(Continue reading)

David Garrido | 18 Aug 17:59 2015

Sometimes you just gotta gloat............

Hello All,

I have been on the lookout for a variety of different FLUKE equipment.  And today, it all came together in a
wonderful way.

I went to my favorite local Equipment Surplus Center on the hunt for an HP 6260B DC PSU.  Found one, 40 dollars.
DONE!!!  Or so I thought, until I decided to take one more quick look before leaving with my new to me DC PSU.

While cruising around I spotted what looked like a FLUKE 7105A Calibration System.  You know the
one………….all hidden back in a dark corner.  Well, sure enough it was a 7105A with its full
compliment of test gear.  335D, 845AR, 720A, 721A, and a BUNCH of interconnects.  All of the equipment looks
to be in fine shape and VERY clean.  No busted or bent posts, all knobs and switches intact.  The best
part…………..when I asked how much he would sell it for he told me, “If and ONLY if you take both the
HP 6260B and the 7105A, I will give it to you for $250 cash total.”

Needles to say, I could not get my pocket opened fast enough…………out flew the cash and the gear was
even loaded into the back of my truck for me.

It has been a VERY good morning gentleman, a very good morning indeed.

I do have a question regarding all of the FLUKE cables that came with the 7105A:

These are the part no’s:

(Continue reading)

Dan Kemppainen | 17 Aug 19:34 2015

Re: Building a high resolution DAC


20 bits is ~1ppm resolution. 1ppm is pushing stability for most 
references, is it not? I would think that at 24bit or more the reference 
is more of an issue than the DAC itself. As I recall, sub PPM/C 
references already eat up your budget and then some! One would guess 
that as soon the fundamental question of how to build one is answered, 
the details would quickly stack up against you.

If the control loop is very slow (I'm making the assumption this would 
be used as oscillator steering EFC signal...), long term drift in the 
minutes to hours range would be important, and PPM/C becomes more 
critical than noise, as the higher frequency stuff could be filtered out.

A few PPM reference, some PPM resistors, circuit traces and 
temperature/humidity affecting the circuit board could add up VERY 

Also, once I clear up a few projects here, I would be interested 
participating in such a project!


On 8/17/2015 10:29 AM, volt-nuts-request@... wrote:
> That's the next thing. But I will not worry about tempco until
> the fundamental problem is solved:-)
> 				Attila Kinali
Attila Kinali | 17 Aug 15:16 2015

Building a high resolution DAC


I have been pondering how to build a high resolution DAC over the weekend.
Something like [1] but has the disadvantage of needing a pair of resistors
that have a 1:2^16 ratio. The 1M/15.4R is kind of unwieldy.
Fidling around a bit, I came to the conclusion that using an R-100R ladder
with 4 10bit PWM DACs would be a good solution. 100R and 10k resistors
are readily available in 0.1% 25ppm/°C (and actually quite cheap).
While the first stage gives 10bits, each additional stage gives
approximately another 7bits, resulting in a total of 29bits resolution.
The 3 remaining bits per stage can be used to linearize the whole

Now this is where the problem starts. How do I measure the circuitry
to build a linearization table? The linearity error is dominated by
the first stage error which is in the order of 0.1% and thus 10bits.
It would be necessary to measure this to somewhere close to 29bits, but
the best DACs that are readily available are 24bit. Yes, there is the
possibility to build some ADC that could do 28bit, but I am not exactly
keen on building something aking an HP3458 (mostly to avoid the
embarrasment of failing at doing so).

So, the question is how would one calibrate something like this?
Or am I missing something fundamental here?

Thanks in advance

			Attila Kinali

[1] "DC-accurate 32-bit DAC achieves 32-bit resolution",
(Continue reading)