The price of oscilloscopes goes up quickly above 100MHz bandwidth, often placing them out of the budget of hobbyists and small businesses. The analog bandwidth of a scope is defined as the frequency at which amplitude is reduced by 3dB (roughly 30%)

Most oscilloscope lines offer a variety of bandwidth options (at increasing prices) such as 50, 100, 200MHz or 100, 350, 500MHz. In many cases, those are really the exact same scope hardware (the highest bandwidth) but are limited in software to a lower bandwidth. This allows manufacturers to address a broader range of potential customers (they can sell the 100MHz scope to individuals or small companies without undercutting the big margins of their 500MHz scope sales to large companies).

Some manufacturers have made it possible for hobbyists to unlock the higher bandwidths. Doing this voids any warranty or calibration of course, and so most labs or large companies simply won’t do this and if you choose to do it, it’s at your own risk. However, I have done this successfully with scopes from Siglent (SDS1104X) and Tektronix (TDS3xxx) and the results have been pretty good.

TDS3K scopes are older Tektronix models that used to cost a fortune (Tek was long the king of the oscilloscope hill and my favorite). The TDS3K line came in 100, 350, and 500MHz models. Fortunately, you can hack any TDS3K scope to 500MHz. For info on how to do this, look to the always excellent eevblog (here). Note that you will need to downgrade the firmware to 3.39 in order to perform the hack. In a nutshell:

• Install a communications module in the back slot
• Configure for 9600,8,N,1 (local echo on is helpful)
• Check current version: *IDN?
• PASSWORD PITBULL
• MCONFIG TDS3052 (or whatever model you’re upgrading to)
• Reboot the scope

Note too that there are downsides to the TDS3K line like calibration is stored in battery backed RAM (and the battery will eventually die). In general, to continue to use a scope of this age, you should plan to re-cap it (replace all electrolytics) and replace the battery-backed RAM module with a new one.

Siglent and Owon are Chinese companies that make a lot of test gear that isn’t quite up to Tek or Keysight standards, but still offer a great deal of bang for the buck and the Siglent products are often hackable. For info on how to hack the Siglent SDS110x scopes you can also refer to eevblog.

An important question is: how do these scopes perform after the hack, so I tested a Tektronix TDS3012 (100MHz) before and after hacking it to a TDS3052. I also tested a TDS3032 I had previously hacked to TDS3052, a Siglent SDS1104X hacked from 100 to 200MHz, and compared them with an unhacked TDS5054B (500MHz) and an Owon SDS8202 (200MHz). In each case I supplied a 0dBm tone from an IFR 2025 RF signal generator through an admittedly less-than-ideal but short coax cable with BNC connectors. For the scopes without internal 50-ohm termination, I used a BNC through terminator and a 6dB attenuator.

A 0dBm signal terminated in a 50R load should be 632mV peak-to-peak. At the bandwidth limit of the scope, that signal should be reduced by 3dB or roughly 30% (-3dBm = 448mV p-p):

It’s clear that the hacks really do increase the available bandwidth. In the case of the TDS3K scopes, to greater than 500MHz, making them truly the equivalent of TDS305x. I measured a 700MHz signal on a hacked TDS3032 at 466mVp-p so the 3dB bandwidth was even higher than that! The hacked scopes also show the sample rate at 5Gs/s whereas before the hack they top out at 1.25 or 2.5GS/s.

The Siglent SDS1104X (nominally 100MHz) hack also extends its bandwidth to 200MHz; mine was down -1.78dBm at 200MHz and still slightly better than 3dB at 235MHz (-2.88dBm). The trigger was able to lock cleanly out well past 400MHz and measurements remained accurate. Note: the SDS1104X does not offer internal 50R termination so measurements were made through a 6dB pad (reduces signal by half, probe set to 2x) and 50R through terminator.

The old Owon SDS8202 (nominally 200MHz) did remarkably well out past 300MHz, easily outperforming the hacked SDS1104X. Owon makes nice analog front ends! Note that frequency measurement stopped at 200MHz even though the scope was clearly able to trigger on and lock to signals out to 400MHz.

I recently purchased an Owon VDS1022 USB oscilloscope (two of them actually).  I’ve wanted a USB oscilloscope on my desk for a long time.  A USB scope *should* be much less expensive than a bench scope since it relies on the PC for its user interface and processing power, however I’ve tried several low-cost USB scopes and they have been disastrously bad due to low sample rates and awful software.

I ordered the Owon VDS1022 from Amazon for $80 shipped or $108 for the isolated version.  After some initial tests, it looks pretty good!  It’s main constraint is the 100MS/s sample rate, however if you can live within that bandwidth constraint it does quite a good job.  I fed it sine waves up to 25MHz from my signal generator and it reproduced them faithfully.  Square waves are, of course, tougher since they contain so many (infinite) high frequency components, but up to 5MHz it is very good and even at 16MHz, it does a decent job.  At 16MHz, you’re only sampling ~6 points per cycle so the waveform displayed may be greatly smoothed with higher frequency details lost (for example, you won’t see sharp edges or higher frequency ringing), but it is still good enough for many of my needs.

The enclosure is aluminum and looks and feels solid and high quality as does the USB cable and  the two included probes (although the probes are only rated for 6MHz at 1x and 60MHz at 10x). The rubber bumpers on the end are probably good for portable use; they can be removed and the silkscreen is duplicated underneath.

The software is very nice.  It installs perfectly on Windows 7.  On Windows 10, it was another story; eventually I figured out that after installing the software, you need to plug the scope in and install the driver manually from the Windows Device Manager (find the scope in the device manager and then update the driver (which in my case was in C:\Program Files (x86)\OWON\VDS_C2\USBDRV), once you have the driver installed, the software works well on Windows 10.  Sadly, the software doesn’t work at all on Linux, even under Wine; the issue is the USB driver.  The software is intuitive, fast, and the interface is clean; I never had to refer to the manual.  It measures frequency automatically and they’ve added keyboard shortcuts for some of the most common operations (vertical and horizontal scales up/dn) which are *very* handy…I wish they would add a few more keyboard shortcuts, especially run/stop, single-shot re-trigger, and vertical position.  The software includes an extensive set of automatic measurements under the Math settings including spectrum analysis (FFT); on the big PC screen you can have many measurements active without cluttering the display.

At this price, the VD1022 seems to hit the right price-point for its feature set; it’s a no-brainer to choose it over the Hantek or SainSmart low-end USB scopes.  If OWON drops the price a bit on their faster USB scopes, I’ll probably buy one of those too.

Update: 12/8/2015: I was curious to see if the non-isolated scopes could be upgraded and sure enough, remove 8 resistors and install two ICs for power and signal isolation (U37: ADUM3160BRWZ-RLCT, U9?: DCP20505U) and the scope works and is isolated (at least no DC connectivity)…the cost was just under $40 for two scopes ($20 each).

Update: 7/8/2016: I like these VDS scopes so much that I bought a VDS2064 (60MHz, 4 channel, LAN interface).  I haven’t figured out the LAN interface yet, but I can confirm that it works nicely over USB with Windows 10 (requires the same manual process for installing the USB driver described above).  I now have a VDS on my work office desk, home office desk, and in my robotics backpack.  After purchasing these USB scopes, I haven’t turned on my traditional bench scopes except once to look at a VHF signal (had to use my old 500MHz 5GS/s Tek scope).

Owon needs to start making more USB-connected test gear (signal generator, logic analyzer, etc.) in this form factor!

Update 2023: This post was from 2014; I sold the Rigol scope many years ago. It was great in its day, but I’m sure it’s discontinued and there are certainly better choices now. One of the best value bench scopes today is probably the Siglent SDS 1104X-E; in no small part because, like the Rigol, it is easily hacked. Also like the Rigol scope, the Siglent fan is too loud and I’m probably going to have to address that soon (the consensus seems to be that this is best accomplished by lowering the fan voltage to 9-10v)

Original 2014 post: The Rigol DS1052E is a fantastic oscilloscope and an amazing value at $329.  It is every bit as good as my favorite Tek scopes (maybe even better) at a fraction of the price.  I have previously owned/used budget scopes (Owon, Wittig, etc.) as well as Tek and HP scopes and this is hands-down my favorite.

There is a software-only hack to convert it from 50MHz to 100MHz bandwidth…I’ve done the hack and can confirm it works.

The only problem with the scope is that the fan is 36.5 dBA (very) loud.  I finally got around to replacing it with a 22dBA Xilence 60mm case fan (less than $10 shipped on eBay) and it is now delightfully quiet.  The Xilence fan spec says it moves 30CFM (more than the 21CFM of the original); it is audible, but inoffensively so: mostly noise from the air moving through the plastic case, not from the fan; it is dramatically better than the original fan.  Note: opening the scope case voids the warranty; the process is well documented and requires a T-10 Torx screwdriver (Craftsman 41473) which is also useful for opening Tivos.  I cut the connectors off both fans and used the connector from the old fan with the new fan.

Warning: if you open your scope, please make sure it is unplugged and observe proper AC safety procedures.

Future:

• Try Spectrum Analyzer hack (more info)
• Antenna tuning