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

[Electro Fan]

Just looking for opinions but this will probably bring out some debates....

So, get on your boxing gloves or better yet just be friendly 

What is your preferred least expensive but reliable used-market scope that has at least 1 GHz of bandwidth?

That's it - no other modifiers but you can make your case based on any value-added considerations such as 4 channels vs. 2, color vs. monochrome, LCD vs CRT, less bench space vs. more, good measurement features, or any other features, functions, specifications, real world experience, etc., etc.

[nctnico]

I think Tektronix TDS744A uphacked to 1GHz / 4Gs/s.

[dr.diesel]

Any particular project driving/requiring this?

[Electro Fan]

Any particular project driving/requiring this?

Fair question - what started it was a desire to get to better rise time measurements but I'd rather not constrain a wider discussion of what folks think might be a really good 1 GHz scope in general (while keeping the price down). 

[AndyC_772]

I agree that the Tek TDS7xx series are excellent scopes, and an obvious option if you need 1 GHz on a modest budget.

I had a TDS754D for a while, but it was quite noisy, kept the room warm (400W power consumption), and there was always the threat that its critical battery would finally give out and lose all the cal data. No doubt this can be worked around if you have the time and inclination, but I need my scope to earn a living, so I chickened out and swapped it for a newer Agilent.

[Lukas]

Does a sampling scope suit your needs? If yes, have a look for Tektronix 7000 series mainframes with sampling plugins. Generally speaking, high bandwidth sampling scopes are much cheaper than a realtime scope with the same BW.

[Howardlong]

Recently I managed to buy an HP 54120B mainframe, 54121A test set and cable for a total of $700 + shipping over three separate auctions over the period of about four months. The aim was to be able to look at digital signals over 100MHz and be able to see reasonably what they really look like rather than some hazy representation, Together that's a 20GHz sampling scope. The 54121A has its own TDR pulse generator built in with <=45ps rise time. The 54121A is speced for 17.5ps rise time, if you can generate such a signal. I also bought a 54006A 6GHz passive probe for $200.

With the built in TDR pulse generator I achieve a 33ps system rise time on my unit. It's been pretty educational looking at this stuff in the time domain, usually I use an 8753A VNA for matching stuff, and will continue to do so, but seeing the impedance bumps in the time domain give you a different perspective.

One thing to note is that the trigger is separated from the channel inputs. This means that you need to construct various contraptions out of power splitters and cables. If you really have to see what caused the the trigger (ie, you have a not very repetitive signal) you will need a delay line, and keep in mind that a delay line of sufficient length is going to affect the signal integrity. All this adds to the cost. I finally invested in an SMA torque wrench too.

The 54120B is a big beast, longer than all my other boat anchors, about 25" depth, but not quite as heavy as I expected. It was the 54121A that was the expensive bit. I managed to get mine with the 3.5mm bulkhead savers and shorts attached. These are thread compatible with SMA, but take care on how you mate them, the 3.5mm receptacles don't have the teflon supports on the inner that SMAs do.

Someone's trying to sell the same setup as mine for £25k on ebay at the moment, I don't think so!

[TerraHertz]

Recently I managed to buy an HP 54120B mainframe, 54121A test set and cable for a total of $700 + shipping over three separate auctions over the period of about four months. The aim was to be able to look at digital signals over 100MHz and be able to see reasonably what they really look like rather than some hazy representation, Together that's a 20GHz sampling scope. The 54121A has its own TDR pulse generator built in with <=45ps rise time. The 54121A is speced for 17.5ps rise time, if you can generate such a signal. I also bought a 54006A 6GHz passive probe for $200.

With the built in TDR pulse generator I achieve a 33ps system rise time on my unit. It's been pretty educational looking at this stuff in the time domain, usually I use an 8753A VNA for matching stuff, and will continue to do so, but seeing the impedance bumps in the time domain give you a different perspective.

One thing to note is that the trigger is separated from the channel inputs. This means that you need to construct various contraptions out of power splitters and cables. If you really have to see what caused the the trigger (ie, you have a not very repetitive signal) you will need a delay line, and keep in mind that a delay line of sufficient length is going to affect the signal integrity. All this adds to the cost. I finally invested in an SMA torque wrench too.

The 54120B is a big beast, longer than all my other boat anchors, about 25" depth, but not quite as heavy as I expected. It was the 54121A that was the expensive bit. I managed to get mine with the 3.5mm bulkhead savers and shorts attached. These are thread compatible with SMA, but take care on how you mate them, the 3.5mm receptacles don't have the teflon supports on the inner that SMAs do.

Someone's trying to sell the same setup as mine for £25k on ebay at the moment, I don't think so!

I like these too. I have a couple working, one for US$610 in 2004, another free. Plus another mainframe for spares (power supply problem) for US$75 recently.
Better mention to Electro Fan that these things are 50 ohm input, and absolute maximum allowed voltage range +/- 2V. Maximum, as in more will blow the inputs. This means you have to be extremely careful with static, ensure cable conductors are shorted to ground before connecting to the scope, etc.

The commonly available 'service' manual has no schematics, but Artek manuals does have the schematics for the mainframe available on CD. They are good quality but don't include the sampling head. I still don't have schematics for that.

A really cool accessory is the HP N1020A TDR probe - PCB probing for 54121T. It's very nice to be able to see PCB trace impedance variations along a track. These come up now and then on ebay. eg 181505699415

[Electro Fan]

Thanks

So far it looks like a TDS700 series or a 7000 Series sampling system such as a 7S11 and S-6? 

The sampling system has limited voltage range?

Or try duplicate Howardlong's good find with the HP 54120B, etc.

Any other suggestions/considerations?

[AndyC_772]

www.fastsampling.com

[Howardlong]

The sampling system has limited voltage range?

You use inline 50 ohm pads to attenuate appropriately, or you can use a 54122A instead of a 54121A which has built in variable attenuators but has a reduced bandwidth of 12.4GHz, probably not much of a problem if you're probing with a 6GHz probe though.

Edit: I come with an RF background so have a reasonably large selection of SMA pads and other related paraphernalia already.

[EV]

Thanks

7000 Series sampling system such as a 7S11 and S-6? 
...

You need plugins 7T11 and 7S11 with S-2 or S-4. It is easyer to use if the pulse is pretriggered about 70 ns using external trigger.

[Wuerstchenhund]

What is your preferred least expensive but reliable used-market scope that has at least 1 GHz of bandwidth?

It depends on what you want to do, really. 1GHz bandwidth is pretty meaningless if the other specs aren't adequate for the task at hand.

If usability was at least somewhat important then I'd say a LeCroy 9370/9374 or 9384, simply because while they are old and ugly, they offer very decent specs (1GSa/s to 4GSa/s real-time sample rates, 50k to 8M sample memory per channel), and for a few bucks can have all their advanced options enabled.



On the other side quite often the successors LeCroy LC574 (4GSa/s) or LC584 (8GSa/s) can be found for the same price as a 9300 Series scope. The LC offers faster processing and color screen, and like with the 9300 Series these scopes can have all their software options unlocked for a few bucks, too.



Both are pretty reliable scopes for which Service Manuals including schematics are available, and especially with the advanced options enabled they can still do lots of things that even today can only be found in high end scopes. In this age and (2nd hand) price class there's unlikely to be anything more powerful. Although their age does start to show (i.e. screen burn), and it can take some time to get a good deal amongst all the ebay sellers asking insane prices for their "untested" (yeah, right) gear. But that's a general problem.

However, if money and price was of upmost importance, and usability played no role, then one can save a few bucks by getting one of the antique sampling scopes from the late 80's. They are huge, slow, loud, suck lots of power, and are only really useful for a very limited set of tasks, and due to their age and sensitive components may require a lot of babying, but these days at least they're often dirt cheap.

[EEVblog]

Which country?
$765 buy it now
http://www.ebay.com/itm/Tektronix-TDS-684A-1GHz-5GS-s-4-Channel-Color-Digital-Oscilloscope-13-1F-2F-/371470646243

[bingo600]

Which country?
$765 buy it now
http://www.ebay.com/itm/Tektronix-TDS-684A-1GHz-5GS-s-4-Channel-Color-Digital-Oscilloscope-13-1F-2F-/371470646243

Whoaaa - The UPS shipping offered costs $550 for DK.
Thats 72% of the scope price, and both prices would be used, when adding the 25% DK import VAT here   

/Bingo

[Fungus]

Whoaaa - The UPS shipping offered costs $550 for DK.
Thats 72% of the scope price, and both prices would be used, when adding the 25% DK import VAT here   

Yes, I saw that.

It's $26 if you're in the USA, $550 if you're not. I think a pegasus will fly it to your house or something.

[nctnico]

Which country?
$765 buy it now
http://www.ebay.com/itm/Tektronix-TDS-684A-1GHz-5GS-s-4-Channel-Color-Digital-Oscilloscope-13-1F-2F-/371470646243

I would not get that one because it has no peak detect (AFAIK the entire Tektronix TDS600A series has no peak detect) and it has a very short memory. Without peak detect a DSO is very limited in it's use. A TDS500 or TDS700 series is a much better buy!

If shipping is expensive, ask if they can ship using USPS.

[woodchips]

Be warned that many > 500MHz scopes struggle to trigger. In particular the HP 54120 gives up at 1GHz even though the amplifiers will work to 18GHz.

The old HP180 series scopes have sampling,as do the Tek 540 and 560 sopes.

Undoubtably the best is the Tek 7000 scopes, trigger to 14GHz, wonderful.

The other sampling wrinkle that is very useful is that because they don't have amplifiers, then the frequency response doesn't roll of at 12dB or so. I have had usable traces from the S2 sampler at more than 10GHz.

[Howardlong]

What is your preferred least expensive but reliable used-market scope that has at least 1 GHz of bandwidth?

It depends on what you want to do, really. 1GHz bandwidth is pretty meaningless if the other specs aren't adequate for the task at hand.

...

However, if money and price was of upmost importance, and usability played no role, then one can save a few bucks by getting one of the antique sampling scopes from the late 80's. They are huge, slow, loud, suck lots of power, and are only really useful for a very limited set of tasks, and due to their age and sensitive components may require a lot of babying, but these days at least they're often dirt cheap.

Totally agreed, you definitely wouldn't want to use one of the sampling scopes as your day to day scope for general development and debugging. But if you want to look at rise times, eye patterns and signal integrity for sub-nanosecond stuff such as USB 3.0 without the measuring instrument itself affecting your measurements too much then they have their place. But no, I certainly don't switch it on every day, far from it in fact. I do admit to a strange fascination of seeing changes at 10ps/div.

To extend the triggering of the 54121A to 18GHz, you can use a 54118A. The basic 54121A triggers to 2.5GHz, but you'll need a 200mV p-p signal to do that (keep in mind the various attenuations from power splitters and probes). Minimum pulse width for the 54121A trigger is 200ps @ >200mV.

[Wuerstchenhund]

Totally agreed, you definitely wouldn't want to use one of the sampling scopes as your day to day scope for general development and debugging. But if you want to look at rise times, eye patterns and signal integrity for sub-nanosecond stuff such as USB 3.0 without the measuring instrument itself affecting your measurements too much then they have their place.

If it has to be as cheap as possible or the bandwidth needs to be very high, I agree that they have their place. But even for eye patterns I'd rather use a real-time scope, either in real-time mode (real-time eye) or in ETS/RIS mode (where they still offer better performance than most sample scopes).

But no, I certainly don't switch it on every day, far from it in fact. I do admit to a strange fascination of seeing changes at 10ps/div.

Well, that's the other part (the fun of fiddling with old instruments), which isn't necessarily guided by necessity, and where normal use-case based criteria don't apply.

The 54120 is certainly an interesting scope, although a very specialized one.  I wish I had the space for one.

[edavid]

Thanks

So far it looks like a TDS700 series or a 7000 Series sampling system such as a 7S11 and S-6? 

If you want reliability, I don't think you want a 7000 series sampling setup

You could also consider a Tek 11801, which is similar to the HP 54121, but uses plugin sampler heads instead of the separate box.

[robert_]

Id go for Lecroy 93xx over a TDSxxx any day.
Nice large CRT display, long memory (nothing <50k/channel, and up to 8M on some) and seem to be much more reilable, no leaking SMT capacitors. Also you get full service manuals incl. schematics, which Tek doesnt.

Also, 1Ghz: Tek 7104. Huge, loud, power hungry, but its a 1Ghz realtime analog scope. Not that it would be too useful, but it exists.

[Electro Fan]

Thanks

7000 Series sampling system such as a 7S11 and S-6? 
...

You need plugins 7T11 and 7S11 with S-2 or S-4. It is easyer to use if the pulse is pretriggered about 70 ns using external trigger.

I think the 7000 is the preferred route....  It seems that the 7T11 and 7S11 are not both needed, seems like 7S11 should do it, yes?  Then comes the question of what are the tradeoffs between S-6 and say S-4, 3, 2, etc?  And finally, which probe?

Any info/suggestions along these lines would be very welcome.  Thx

[dom0]

You absolutely require both a 7T11 and a 7S11 for a sampling scope.

[Electro Fan]

You absolutely require both a 7T11 and a 7S11 for a sampling scope.

Wow, I definitely missed on this.  Thanks for the heads-up.