Recent Posts

1

Projects, Designs, and Technical Stuff / Re: TekBox TEM cell – how is it constructed ?

« Last post by tomud on Today at 10:58:10 pm »

For those interested, I found a scientific article that explains this problem a bit (attached).

Personally, I'm waiting for the PCB I ordered, so I'm not able to write more at the moment. The PCB is modeled after the TekBox septum - I based it on the photos I found on the Internet (we'll see what the results will be).

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Test Equipment / Re: Tek 2465 Horizontal Sweep Issue

« Last post by kellymcdonald78 on Today at 10:54:59 pm »

Not sure exactly what changed (reseating U700?) but my sweep is back

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Repair / Agilent 3458A 8.5-Digit Multimeter Repair, Teardown & IC Analysis

« Last post by Hugoneus on Today at 10:50:52 pm »

You can watch the video here: [30 Minutes]
youtu.be/VTocNUyGIWM





** SPOILER **

In this episode Shahriar repairs a faulty Agilent 3458A. These highly desirable multimeters have continued to climb in price in the past few years. The last time The Signal Path has repaired one of these units was back in 2018.

This instrument generates several errors both during power up as well as Auto Cal procedure. The error points to a failure in the OHMS measurement mode. Detailed instrument block diagram and schematics are examined. Measurements also show incorrect DC current sourcing during OHMS measurements and the associated circuits are closely analyzed. The problem is traced to a quad-comparator IC. Replacement corrects all problems during ACAL. The battery backup of the SRAM ICs are also replaced to eliminate non-volatile errors. The IC of the comparator chip is also extracted and examined under the microscope.

The repaired instrument performance is verified by using voltage, current and resistance standards.

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Projects, Designs, and Technical Stuff / Re: ANITA MK IX Restoration

« Last post by SL901B on Today at 10:41:53 pm »

That's fair! I'll have to cross that bridge when I get there, I get that most components weren't built to last ~60 years haha

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Buy/Sell/Wanted / Re: SOLD — Learning Art of Electronics course kit

« Last post by YetAnotherTechie on Today at 10:31:37 pm »

Just a few days someone was looking for PCB design files, program code, Microcontroller Code, etc. because he couldn't find them anywhere anymore. Do you have them?

https://www.eevblog.com/forum/buysellwanted/tom-hayes-the-art-of-electronics-hands-on-lab-course-program-and-code-listings/msg5442092/#msg5442092

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Test Equipment / Re: Magnova oscilloscope

« Last post by KungFuJosh on Today at 10:24:47 pm »

Including 19% Tax...

https://www.batronix.com/versand/oszilloskope/Siglent-SDS2354X-hd.html

Oh yeahhhh. Forgot about that ridiculous VAT thing. Yikes.

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Projects, Designs, and Technical Stuff / Re: (Yet Another) DIY Multislope ADC

« Last post by Kleinstein on Today at 10:19:05 pm »

The rundown part is only a relatively small part of the result. The question is only if the reference for the rundown are more accurate than a high resolution ADC and stable capacitor, that would be the alternative.
If the postive and negative reference are the same size, not extra constant is needed to calculate the result. Ideally the difference between the reference (including a possible offset of the integrator input voltage) is an additional correction parameter, that has a limited effect. Measuring that parameter is relatively simple by comparing the case of no reference and both references at the same time. It is a little extra effort for a kind of "factory calibration", but the later math is not so bad.  No need to go above some 16 bits, as the rundown part is still only a relatively small part of the result.

How would a fully symmetric rundown look like ?  Only one direction and thus a comparator reading from both directions is not really a good option. It adds the comparator hysteresis / delay problem and also the problem with a very short pulse close to zero initial charge.
A fixed sequence with 2 variable times is kind of the natural choice. The system is fully determistic. There is no big difference from starting positive of negative. At zero res. charge one gets 2 short pulses and when away from zero one of the pulses gets longer and the short one stays the same.  There is just some freedom in the design on how short the pulses can get. Adding a few more cycles there is usually not such an issue.
A possibly tricky point may be the effect of short pulses in the runup. This way the runup steps may be tiny bit different from just the ref. strength and time. In the shown simple runup scheme the number of short pulse directly follows the runup result and a slightly modified cal. constant could compensate. With not too fast a modulation and thus enough time for the short pulses this should still not be a problem.

8

Test Equipment / Re: Magnova oscilloscope

« Last post by Martin72 on Today at 10:17:15 pm »

Including 19% Tax...

https://www.batronix.com/versand/oszilloskope/Siglent-SDS2354X-hd.html

9

Microcontrollers / Re: Signal filtering - Could this work ?

« Last post by gf on Today at 10:16:54 pm »

But it has smooth cut-off slope on frequency response and pretty mediocre rejection ratio at stop bandand, which is not suitable for many DSP applications.

Yes, the selectivity and stopband attenuation are not good.
However, you won't find a FIR filter of the same length that has a better (lower) equivalent noise bandwidth (ENBW).
If noise reduction is the only goal (and selectivity is not important), then boxcar averaging over the entire desired settling time is still the best choice.

Another advantage of a FIR filter is a bounded 0-100% step response settling time, while the settling of an IIR filter is asymptotic. Example: An exponential moving average filter which settles to (say) 99.9% within 30 seconds has an even worse selectivity and stop band attenuation than boxcar averaging over 30 seconds (whose step response settles to 100% in 30 seconds), and the ENBW of this exponential moving average filter is ~3.45 times higher, too. Frequency response is attached for comparison.

10

Beginners / Re: buying a oscilloscoop

« Last post by Zenith on Today at 10:12:43 pm »

It comes with probes, probably 100MHz and switchable between 1X and 10X. Mostly the 10X setting is used. I'd guess your friend recommended 100X probes as well, because you work on tube amplifiers and radios.

A way to become comfortable with it is to play with it with a signal generator or function generator. It doesn't have to be a very good one. If you don't have one, a £10 XR2206 based function generator from ebay would do, or you could put something together with a 555 timer chip, or make a multivibrator.