Keithley 2700 - Repair 2.

After some serious issues with the local post, Today the new mains transformer of the 2700 landed in my hands.

So I measured a bit, then installed into the unit.

Actually it was pretty straightforward. Everything connected, assembled.

After some warmup I compared with my 7.5 digit Keithley 2010. It looks like spot on (the Digistant source not really able to keep with them).

Repair Manifesto

I just found this in a group. I can't resist to share it.

Reference Resistors

A friend of mine asked me for a quick project (finally it become not so quick, but just because the time it required the parts to arrive).

He is installing pool and other water handling related systems. One of the pool measure system has PT100 temperature sensor input what need calibration. The proper calibration equipment cost a fortune. Actually he only need two reference point. For this he asked me to make some reference resistors in a box what is precise enough and has low tempco.

The values are 100 ohms and 119.4 ohms what is weird a bit. Looked around and find the required resistors in 0603 and 0805 size (100 and 120 ohms 0.01% 2ppm) around $10 each. For the 119.4 ohms I planned 24k in parallel with the 120 ohms (bit less precision as there is not needed better).

I bought some tiny aluminum boxes from the AliExpress. The idea to change the front plate of the boxes to a PCB add the screw-in banana sockets and put the resistors to the back of the boards.

It looks like this:

It was manufactured by PCBWay in the usual excellent quality - Thank you!

I was a bit afraid, if they can follow my request and put the order number to the already crowded component side, but it was managed without problem. It arrived together with my VFD project board, what I'll write about later.

The board soldered (Yes, it is a joke. Only one single resistor in this case)

Some measurements

If I count the cable and the plugs contact resistance is the result get even better. I'm satisfied with the result.

And the final boxes (the request was about two units.

I put two resistance values into a single box. The only thing left is to print some labels on it with the values.

Spectrum Analyzer

It is itching. Yes, you can tell: scratch it.

Actually I'm in a debate with myself. As I read more, more confused.

I need a Spectrum Analyzer. Or maybe not. Yes, I had an HP ESA, but sold it. It was a 75 ohm model with a frequency range doesn't go below 1Mhz, what is I felt is a no go for me. Yes you can tell that those things can be handled, but it is too late. It is gone, so look into the future.

What I need an SA for

• Audio measurements. I need to cover let say from 10Hz to 100kHz. Yes, this is wider than the audio range, but it is good to know, what the electronics do outside it.
• SMPS measurements. I'd like to characterize the noise of the things I buy or build, get EMI probes, etc. No, I don't need it for FCC or similar acceptance, just to know, what I bought it a quality unit, or a heap of crap. I guess the frequency range is from 20kHz to a few MHz. Also I intend to find out, the ideal frequency of unknown SMPS transformers. I guess later also need a tracking generator.
• Characterize frequency references. Lately I was playing with rubidium standard, I have also a few OCXOs in my parts box, for later use. Intend to build a GPSDO or similar unit. Those things are running around 10MHz
• Repair characterize maybe calibrate AM/FM generators. It happened to fall four Panasonic/Levar VP-8193A/D onto my bench. All of them has issues in the RF section (looks like the control part works perfectly, the LF part I didn't check yet). For repairing, later calibrating it. For those I need a frequency range from around 100kHz to around 200MHz. It also need analog modulation analysis for AM and FM.
• Sub GHz and GHz digital communication. It is in my mind to play with 433kHz, 868kHz, ZigBee, Z-Wave, LoRa, Bluetooth and WI-Fi. The sub GHz can be handled by most of the analyzers but the 2.4GHz is a different story. Also those things are requiring some kind of Digital Modulation Analysis, what not all of the SA has.

What test equipment or similar have I currently

• Hack-RF SDR https://greatscottgadgets.com/hackrf/one/. It is by design is not a test equipment. I need to figure out, get some advise, if I can use it for any of the functions above. It maybe good as SA, AMA, DMA for the RF range, but has no idea what can be achieved with it or even good enough for measurements. Didn't use it up to know just have it in the drawer for a while.
• Boonton 8201 Modulation Analyzer. Probably good for the AMA function (if it works, not yet tested)
• Rigol MSO-5074 (with all of the options added, so it is a highly capable 4 Ch, 350MHz, 8Gsps oscilloscope). I think the FFT function can be good for some of the low frequency measurements, but I'm afraid of the ADCs 8bit resolution for this kind of sensitivity required work.
• HP 35665A Dynamic Signal Analyzer. Probably good for most of the audio related work together with the other audio equipment I have
• Steinberg UR22 mkII external sound card. Plan to use for audio. There are quite capable software available for free online, I also have a measurement microphone, power amplifier, Dayton DATS v2 to extend the capabilities of the computer based measurements.
• HP 8903B Audio Analyzer. This is a highly capable unit, but unfortunately I can't count on it currently as it need repairs/calibration. The linearity in the frequency range is a way off even just connected its generator output, to its input
• Keithley 2015 THD multimeter. It is able to commence some of the functions of the 8903B.

What options I have

Actually I targeted the budget max €1500+VAT.

1. Doesn't buy anything just try to utilize my current equipment for the purpose above. It may work, but deffinetely need some advise, starting points for information.
2. TinySA Ultra. It is probably able to fulfill most of my RF needs. I just not yet know if it has drawbacks other than the small display. Some more research will be needed.
   https://eleshop.eu/tinysa-ultra-spectrum-analyser.html
3. Owon XSA-1015P-TG. It seams to be a great unit. I checked this video: 
   
   
   
   It looks like, on most of the parameters it is better than the Rigol (I was considering previously, but based on my research I dropped it already). For €975 it is a great deal https://eleshop.eu/owon-xsa1015-tg.html.
4. Siglent SSA3021X-Plus. This is a similar unit as the previous Owon, but it cost a bit more €1469 https://eleshop.eu/siglent-ssa3021x-plus-spectrum-analyzer.html.
   
   
   
   
   
   It has upgradability to 3.2GHz (covering the Wi-Fi and Bluetooth band), has AMA and DMA option. I didn't see any of those in the Owon specification.
   But still, there are some things I miss in both of the units:
   
1. Not covering the audio band
2. The TG minimum frequency on both units starts at 100kHz, what is too high for testing SMPS parts.
5. Signal Hound SA44B Spectrum Analyzer + TG44A Tracking Generator. Those units together are bit above the budget what I willing to spend ($1930 together) https://signalhound.com/products/4-4-ghz-scalar-network-analyzer/
   It looks like resolve my low frequency questions as it start at 10Hz (both the SA and TG).
   I'm a bit afraid being solely PC based USB device, and not yet sure if all of the functions are available I'd like to have. Actually I found a review video on it.
   
   
   
   
   

   I not yet watched it as it is two hours long. I should find the time before I decide.

So, here I stand today. Bit more confused than a few days ago, when I started to look.

If you have any ideas, thoughts on this, please let me know. I really would like to get some hints on this.