FFT analyzer recommendations

I think Gerhard is interested in measurements in the 0.1Hz region and below, where your preamp would be about 26dB noisier than the one he's working on.

I've used a number of 89410A devices, and they have exhibited some spread i n the noise floor. Usually the flat part is around 8-9 nV/sqrtHz, and the 1 /f corner could be in the kHz or tens of kHz. One device had popcorn-like n oise in one channel.

With a preamp built of 4 paralleled ADA4522s and LT5400 resistor arrays, I managed to get noise floor of about 5 nV/sqrtHz flat down to a few mHz. If there's interest, I can dig up those measurements. I used it to measure exc ess 1/f noise in resistors hooked up in a biased Wheatstone bridge, like th is:

Another nice trick with the 2-channel FFT is cross-spectrum measurement. Wi th two good preamps and some patience it buys you another 10-20 dB downward s:

se_in_chemical_batteries

Cheers, Nikolai

Am 17.03.2018 um 21:16 schrieb Castorp:

That would actually be good news, that the noise comes from the input amplifiers. That would mean that one can use cross correlation on the two channels. I had some fear that it might be phase noise from the sampling clock since it is probably synthesized. That would be common to both channels and would not average away.

Yes, especially the setup of the 89410.

Wheatstone bridge, like this:

Thanks to plowing with the power of a thousand chicken my setup is only abt. 10 dB worse than that of Fred Walls, but without cross correlation. I still can add that.

1000 chicken means averaging over 20 ADA4898 op amps :-).

If you want numbers on batteries that you actually can buy and not some anonymous thingies that they happened to have in the lab, there is

< >

It is still limited by the 1/f of the 89410A and the undersized input capacitor of the preamp (160 uF foil). I have replaced the foil caps with wet slug tantal, 4700 u IIRC, but that is only a good decade better, just a drop in the bucket.

An array of organic polymer electrolytics was too leaky. An array of wet slug tantals costs too much if I have to pay for it from my own money. :-(

BTW, two 3.7V Panasonic lithiums are quite OK, noisewise. They seem hard to top. <

>

0 dB is 1nV / rt Hz, DC voltage is 7.3V. The 60 Ohm 1nV/rt Hz reference resistor and the short switch are on the amplifier side of the coupling capacitor, so everything looks much better.

The picture of the batteries is to the right.

cheers, Gerhard

ad in the noise floor. Usually the flat part is around 8-9 nV/sqrtHz, and t he 1/f corner could be in the kHz or tens of kHz. One device had popcorn-li ke noise in one channel.

, I managed to get noise floor of about 5 nV/sqrtHz flat down to a few mHz. If there's interest, I can dig up those measurements. I used it to measure excess 1/f noise in resistors hooked up in a biased

. With two good preamps and some patience it buys you another 10-20 dB down wards:

Batteries.pdf

535945536/

Thanks, Gerhard. You've done quite a lot of good work in this field.

I've always tried to avoid AC-coupling and its associated problems. With ne ar-zero voltages (e.g. balanced bridge), you can survive with some amount o f offset, or fix it in between the gain stages. For batteries I've tried (w ith variable success) to measure two of them back-to-back, in counter-serie s.

The point of my 4xADA4522 preamp was not to get super low white noise (5 nV /sqrtHz is nothing to brag about), but to have no 1/f. It was all DC-couple d, including the 89410A in its most sensitive range (10 mV I think). With a n upper frequency of 1 Hz and 3201 frequency bins (the maximum), it takes o ne FFT in more than an hour. With overnight averaging it gets smooth enough to make sense.

I'll find those details in the next days, some of them are in my work labbo oks.

Cheers, Nikolai

So, here's the device with popcorn noise in one of the channels:

The second device is my own 89440 - the only one I have access to right now . Channel A is clearly better in terms of LF noise. The magenta curve is cr oss-spectrum.

All these measurements are on the finest range, 1MOhm inputs with external short, DC-coupled.

I coulnd't find the ADA4522-1 preamp measurement files, but I found notes o n the setup. The preamp was followed by an SRS amplifier, and the total gai n was 10000. That was enough to ensure flat floor down to a few mHz, but ar ound there it did intersect with the 89440A 1/f noise. For my purposes back then it was fine.

All of the batteries I tested showed steeper than 1/f behaviour at low freq uencies, so they were not good enough as a DC source for my tests. And I di d it carefully - temperature-stabilized oven, no stress, mechanical relief, plenty of time to settle, etc...

Cheers, Nikolai

Am 19.03.2018 um 11:28 schrieb Castorp:

Hi, Nikolai, thanks for the information.

I'm just plowing through the 89441A programming manual to upgrade my control program. The manual leaves of lot of open questions, the only thing they say again and again is that I cannot use options that are not built-in.

regards, Gerhard

Hi Gerhard, i have also bought one of these units, 89441A, no serial cable and for the love of peet, i cannot find the cable connection diagram, and standard RS232 didnt work either, could you help out and show me how to do it please?

Thanks!

Arjen.

Another question of interest, what's the next, more modern version of this instrument, one could look for on eBay?

--
 Thanks, 
    - Win

I made my own cable and it works. It's just a 1:1 connection with DB-9 on both sides, without any crossing of the TX and RX lines. I can double-check tomorrow but I'm almost sure there's nothing else.

Cheers, Nikolai

It's a straight-through D-25 cable.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

I think the 89441A was the last one with a baseband input.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

What's its floppy drive? A weird HP LIF format? Can you get the "Standard data format utilities"?

--
 Thanks, 
    - Win

No, it's a DOS DS/DD 1.44 MB unit. You can make decent-looking TIFF plots e asily, but (unlike e.g. my TDS 784As) you can't get the measurement data in a plain text file.

Cheers

Phil Hobbs

:

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ble and for the love of peet, i cannot find the cable connection diagram, a nd standard RS232 didnt work either, could you help out and show me how to do it please?

both sides, without any crossing of the TX and RX lines. I can double-chec k tomorrow but I'm almost sure there's nothing else.

Hi Nikolai, thanks for your reply! i have tried to wire it true straight, but that did not work, i just connected pin 1 to pin 1, pin 2 to pin 2, ET C. i stopped getting the error at start-up when i omitted pins 1-6-9, but then when i want to measure something requiring the RF section, it gives a communication error. having said that, it seems that the shielding requir ements and cable quality requirements could be high, im using two rather Ch inese DB9's and un shielded cable

any advice is most welcome!

Thanks so far,

Arjen.

I'm currently in southern France, so i cannot check anything. :-)

I use it over LAN only. If the 441A has the network option, you just open port 50?? on 192.168.178.111 or whatever and then you can read and write GPIB commands/data from/to it. The network is old style Ethernet on BNC, so you need a converter box. I had to terminate both ends of the RG58 cable, even if the cable was only

10 cm long.

I have written a program that runs on Linux, maybe others. It controls the 441A and does sweeps over seven decades & creates gnuplot output with dB / log-f axes. That involves at least 7 different sweeps and it sorts the data together.

This is open source.

cheers, Gerhard

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ble and for the love of peet, i cannot find the cable connection diagram, a nd standard RS232 didnt work either, could you help out and show me how to do it please?

Sounds cool Gerhard! just to make things clear, the serial cable i need to make is for the serial 2 port that connects the RF unit to the main unit . if anyone can let me know how that is wired, then i'd be very happy. i c an then use the device up to 2.8GHZ. i was really lucky with this buy, the machine i bought is literally brand new.... not a spec of dust inside, no yellowing, perfect.... :-) i will learn allot with this setup!

:

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ough

cable and for the love of peet, i cannot find the cable connection diagram, and standard RS232 didnt work either, could you help out and show me how t o do it please?

d to make is for the serial 2 port that connects the RF unit to the main un it. if anyone can let me know how that is wired, then i'd be very happy. i can then use the device up to 2.8GHZ. i was really lucky with this buy, t he machine i bought is literally brand new.... not a spec of dust inside, n o yellowing, perfect.... :-) i will learn allot with this setup!

Sorry about the delay, I was suffering from jet lag yesterday (-:

I assumed we were talking about the same thing - the interconnection betwee n the RF and the baseband units.

Here's what I'm using:

The cable itself is short, about 1 m. It's just unshielded ribbon cable. On one side it's crimped, on the other one it's soldered. Nothing special at all, and it works.

Cheers, Nikolai

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l cable and for the love of peet, i cannot find the cable connection diagra m, and standard RS232 didnt work either, could you help out and show me how to do it please?

eed to make is for the serial 2 port that connects the RF unit to the main unit. if anyone can let me know how that is wired, then i'd be very happy. i can then use the device up to 2.8GHZ. i was really lucky with this buy, the machine i bought is literally brand new.... not a spec of dust inside, no yellowing, perfect.... :-) i will learn allot with this setup!

een the RF and the baseband units.

On one side it's crimped, on the other one it's soldered. Nothing special a t all, and it works.

Thank you Nicolai, oddly enough, i cannot connect with the RF unit, despit e the cable beeing the same as yours. only difference is that i may have r eversed it as well, after testing 1 on 1 2 on 2, etc. no results.

the sub-d connectors are quite poor in quality, it may play a role, but im supprised as to why it doesnt work. just to be sure, can you see if its pin 1 on 1, etc? as i cannot see the whole cable on your image.

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ial cable and for the love of peet, i cannot find the cable connection diag ram, and standard RS232 didnt work either, could you help out and show me h ow to do it please?

s y

need to make is for the serial 2 port that connects the RF unit to the mai n unit. if anyone can let me know how that is wired, then i'd be very happy . i can then use the device up to 2.8GHZ. i was really lucky with this bu y, the machine i bought is literally brand new.... not a spec of dust insid e, no yellowing, perfect.... :-) i will learn allot with this setup!

tween the RF and the baseband units.

. On one side it's crimped, on the other one it's soldered. Nothing special at all, and it works.

ite the cable beeing the same as yours. only difference is that i may have reversed it as well, after testing 1 on 1 2 on 2, etc. no results.

m supprised as to why it doesnt work. just to be sure, can you see if it s pin 1 on 1, etc? as i cannot see the whole cable on your image.

I just checked it with a multimeter. It's 1 to 1, 2 to 2... 9 to 9.

I guess you're using the correct port (Serial 2). So I don't know what coul d be wrong.

Cheers, Nikolai