Good oscilloscope?

Discussion in 'General Technical Questions and Answers' started by KM5PA, Jan 11, 2022.

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  1. K6BRN

    K6BRN XML Subscriber QRZ Page

    GOOD NEWS! Pretty much all readily available higher frequency (500MHz+) Signal Generators are digitally controlled analog instruments.

    Some
    NEW, ham-accessible DDS (direct digital synthesis) Waveform/Function Generators, like the Siglent SDG2042X , 82X and 122X can put out a very clean, signal-generator quality sine wave up to about 40 MHz, but many can't. Note that even the SDG2042X can be easily "hacked" (see EEVBlog) to hit 120 MHz with a sine wave output. But beyond 40 MHz, waveform quality drops off. This is VERY good performance for a Waveform/Function Generator and these models are quite useful at HF, especially since they have dual outputs and multiple, programmable waveforms. They also plug into and integrate with many Siglent 'scopes to allow easy automated frequency response sweeps of traps and filters. Very handy.

    Beyond that, older used Signal Generators, usually $350 and up, already ARE analog inside, even though they can have handy and precise digital controls over frequency, modulation, sweep, etc. Even brand-new instruments in the $10K range are still mostly analog/PLL based inside, due to the need to keep signal purity high and phase noise low.

    So, if by "analog" you mean really inexpensive plastic pointer over printed scale units, controlled by a big black bakelite knob, those are not really worth owning, old or new, as they generally suffer from major frequency drift and serious signal quality issues. If you simply mean an analog instrument that is digitally controlled - not to worry - just about ANY signal generator you pick up will be analog inside.

    Do NOT confuse a Signal Generator with a Waveform/Function Generator. The former instrument (Signal Generator) emphasizes sine wave signal quality to very high frequencies and often supports AM, FM or PM modulation. In contrast, the latter (Waveform/Function Generator) is all about generating square, triangle, sine and arbitrary waveforms at much lower maximum frequencies and with much poorer sine wave signal quality. Older digitally synthesized function generators, even those by very good companies like WaveTek. had really ugly output quality. A few of the newer breed Waveform/Function Generators, like the particular Siglent units mentioned above, can substitute in for a Signal Generator at lower frequencies, but in general are still not a great substitute for a good signal generator in demanding applications.

    Note that really, really cheap ChiCo "signal generators" listed on Ebay and Amazon are usually just very poor single-board digital function generators inside a bigger plastic case. You really do get what you pay for.

    Brian - K6BRN
     
    Last edited: Jan 14, 2022 at 8:58 PM
    N8VIL likes this.
  2. G0HZU

    G0HZU QRZ Member

    Yes, I agree. There are a lot of people who are stuck in the past. If I had to choose between a modern DSO or an ancient analogue scope then the DSO would be the obvious choice for me by a huge margin. I rarely use my old analogue Tek 465 but there are times when it really does still earn its keep. So I prefer to have both. If I was a student again I wouldn't hesitate to buy a modern DSO first. I'd expect to be able to find an old Tek 465 for £50 or less so I'd still end up with both eventually :)
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    That was back in the day when the "B" meant Better. :)
     
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  4. K6BRN

    K6BRN XML Subscriber QRZ Page

    I do not mean any insult to Tek 465 owners - I've been one myself. But as a user in both a hobby and professional environment, and as an equipment pack rat (this is a serious disease), I do have a strong opinion.

    Put the 465 right next to a 465B and compare the two when monitoring the same signal. Once you do, the 465 will be likely be phased out. By you. Been there, done that.

    Early in my career, we had quite a few 465s on our benches. and when the newer 465Bs began to show up we cleared the 465s off our benches as fast as possible, because the traces on the 465Bs were that much cleaner. In fact, once you really noticed the difference, the 465s became annoying. Otherwise, the two models were close to (but not quite) identical. Management had a bit of a fit (people were fighting over the 465Bs) and we had to bring in a representative from the Cal group to show that the 465 trace could not be "tweaked" to match the 465B. So management went back into their capital equipment budget and replaced the rest of the 465s. Later, the Tek rep admitted that trace quality had been one of the major improvements that went into the 465B model.

    Today, at local swap meets, the 465s command significantly lower prices, not just because they are older, but because the 465B trace is so much better. Or at least CAN be better if both models are in good operating condition. Both models are decades old, now, so anything is possible.

    That said - if you feel your 465 is adequate for your work, then it is. Period. Only you can make that decision.

    I kept one at home myself, until about five years ago when I gave it away.

    But I wouldn't advise anybody to buy a 465 today, when the much better 465B is still readily available (they were made in great numbers). Or even better, a good, modern DSO.

    Brian - K6BRN
     
  5. G0HZU

    G0HZU QRZ Member

    To put this into perspective none of the 465/475 models were trailblazers in terms of trace quality and these models were always fairly average in this respect. I think it was something to do with the tube design/dimensions. Older scopes like the ancient 5 series (eg 585) had very good trace quality in comparison. I used lots of 465 and 465B scopes in my first job and don't remember a huge difference in trace quality. I do remember how high the trace noise was on a brand new 2465 scope in full 300MHz BW mode. My boss lent me his 2465 when he was on holiday and after trying it out I quickly put it back on his bench and went back to using a 465.
     
  6. G0HZU

    G0HZU QRZ Member

    It's really difficult to capture the trace quality of my old Tek 465 with a camera but I've had a go. See the image below. I bought this Tek 465 nearly 30 years ago for just £52 as it had loose front panel controls and also needed a service. I spent a couple of days going right through the service manual to set it up. Since then I've never bothered to service or recalibrate it internally. In all that time a capacitor has failed and one of the front panel controls became loose and had to be tightened. Apart from that I just use it when needed.

    I think the trace quality below is fairly representative of a Tektronix 465. It won't be the best 465 out there but no way would I describe this scope as having a broad fuzzy trace. It just looks like an average analogue scope to me. It does look slightly crisper to the naked eye as my camera will inevitably add a small amount of blooming. however, I've tried quite hard to show that this old scope can deliver a fairly decent trace quality. If trace quality is a top requirement then I'd look elsewhere. A 465 or 465B is only average in this respect.

    [​IMG]
     
  7. K6BRN

    K6BRN XML Subscriber QRZ Page

    Jeremy (G0HZU):

    Your 465 trace looks much better than the ones I used early on and the personal one I gave away - but then, trace intensity seems to be turned WAY down as well, which always helps.

    Regardless - if it's good enough for you, great! You already know my opinion on the matter.

    Best Regards,

    Brian - K6BRN
     
  8. K6BRN

    K6BRN XML Subscriber QRZ Page

    P.S. Best trace I've ever seen on an analog 'scope is a Tek 7104 mainframe equipped with a microchannel plate CRT.

    Brian - K6BRN
     
  9. W9WQA

    W9WQA Ham Member QRZ Page

    explain sampling for me...compared to a reg scanning scope..
    i use dso scopes but dont know how they work.

    no help
     
  10. G0HZU

    G0HZU QRZ Member

    Thanks. The trace intensity is actually set to a normal level because I had to shine a light directly at the scope to try and get a natural image. I used an old and cheap camcorder to capture the image so it needed lots of light. This makes the image look a bit washed out but it was the best I could do. I don't know much about the history of the 465 but apparently the very early ones (1972) weren't as nice as the bulk of the 465 production run. Also, I understand that if they are taken apart and not reassembled correctly the 465 is prone to noise pickup at the front end. Note also that I have the scope in full 100MHz bandwidth mode in the image above. If I turn up the intensity much more it still looks good to the naked eye but the camera starts to bloom. I need a better camera...

    The big old Tek 585 I bought as a student has the sharpest trace I've ever seen on a scope. I believe the 350MHz Tek 485 has a nice CRT as well. I doubt it would compete with the 585 though.
     

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