Least expensive but reliable used-market scope with at least 1 GHz?

[AndyC_772]

I'm not sure I see how a SA can really replace a time domain measurement.

If I'm probing a high speed signal, chances are it's to see if it's monotonic, or perhaps to check the timing relationship between one signal and another. I can't remember any occasion when I've needed to simply measure rise time.

[KE5FX]

I'm not sure I see how a SA can really replace a time domain measurement.

If I'm probing a high speed signal, chances are it's to see if it's monotonic, or perhaps to check the timing relationship between one signal and another. I can't remember any occasion when I've needed to simply measure rise time.

It's just a matter of whether you're doing more RF stuff than digital, or vice versa.

[Rupunzell]

Very much a matter of what needs to be measured and done.

Ghz time domain interments have evolved due to the need for Ghz digital that has become common today. These time domain instruments have their place and fills a particular need. Much the same can be said for frequency domain instruments. They offer a different means of measurement. Neither actually replaces one or the other once the measurement needs become more specific. Out of this appears the mixed domain instrument offering both time and frequency domain.. except it excels at neither as a result of inherent technology trade offs.

Ideally one would have access to a really good time domain instrument, frequency domain instrument and a really good network-impedance analyzer for the specific range frequency spectrum range needed.

Beyond this, skill, experience, knowledge, of the user makes all the difference in getting measurement results. Oh, there is also a host of adapters, cables and endless made up test fixtures and all that to make specific measurements required.


Bernice

I'm not sure I see how a SA can really replace a time domain measurement.

If I'm probing a high speed signal, chances are it's to see if it's monotonic, or perhaps to check the timing relationship between one signal and another. I can't remember any occasion when I've needed to simply measure rise time.

It's just a matter of whether you're doing more RF stuff than digital, or vice versa.

[Mosaic]

While I have a 694c (1M, 1F,2F,13, HD) that stops displaying acquisitions on Ch3/4 on the main time base when triggered, it restarts and all else seems fine once Intensity is enabled with no chip mods.  Also the thermal profile across the trigger chips with the case off is about a 50 °C delta after about 5 mins, with a 6° variance among the chips.  I got the unit for $2k  with a full cal. cert from Axiom test done for free  because of the Ch3/4 issue, which I consider minor now, given it is sorted by a push button.

While the discussion of which scope is better is healthy, for $2k a cal'd 3Ghz one shotter with glitch/ pulsewidth/logic and edge detection gives me  capabilities I cannot afford otherwise in the wifi time domain. I use the analog 24xxA series ($300)  for gen purp work and a Rigol DS2302A (cost $800 with full unlock)  for other deeper memory slower DSO comm/SPI/I2C tasks. The 3 Ghz wakes up when  frequencies of such interest or calibration type work  for other scopes/instruments is required. It's just using affordable toolsets for the right app. A one device that does everything is great but $8K+ scopes are too much $$$. Also at >2Ghz , 50 ohm line impedance dominates and that is often RF Tx line related, at least for me.

For $8K you can get a 3Ghz HP8753D VNA ($2k) , the 694C ($2k) , the Rigol Ds2302A unlock ($800)   the 24xx Tek ($300),  a Rigol 1.5Ghz -TG DSA ($1500), A 6.5 digit Rigol DMM ($600) with change for some good connectors, cabling , probes and such like.

I am seriously considering adding a soldered on heat spreader to the heat solder pad under the TQFP trigger chips given the 1/2" clearance due to the PCB standoff for air flow.  I note that Tek expressly ported the case to cool all the heatsunk chips with fresh air intake but NOT for these 4  trigger chips . Also I will reflow the pins on all  the trigger chips as a precaution to 'stress relieve all the thermal & hygroscopic PCB changes over the years.

Here is my cooling mod. project:
https://hackaday.io/project/12087-tektronix-tds-694c-trigger-cooling-workaround

The TDS694C still goes for quite a lot of money. Unfortunately one of it's problems is the trigger chip overheating and dying. Ofcourse that chip is made from unobtainium. OTOH: you could get lucky buying a replacement chip. A couple of weeks ago I bought a scope which had some custom ASICs which needed replacement and much to my surprise I could buy the chips for a reasonable price... Anyway: it is worth investigation the repair options before buying a TDS694C. Besides that there is also the Tektronix TDS820 (6GHz sampling scope) with the usual capacitor plague.

It turns out that those scopes actually had spare trigger chips on the board.  They were connected to power, but apparently never used for anything. 

I had a spare TDS 694C whose main timebase wouldn't trigger, and a friend who works in the T&M business was able to repair it by moving two chips.  (Both of my original ones were bad.)  I didn't believe him at first, but I haven't been able to find any missing trigger functionality on this scope, so apparently he knew what he was talking about.  Crazy stuff!