Category Archives: Test Equipment

ATtiny

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Every now and then you need an electronic component and there just isn’t a good match available…necessity is the mother of invention so why not make your own? The problem was I had a very tight cost budget, very little PCB space, and was behind schedule…I needed a cheap, tiny solution FAST. Fortunately, I found the ATtiny which is an 8-bit AVR micro-controller available in packages as small as SOT23-6 package (about the size of the head of a pin) that costs $0.28 in small quantity and the more powerful ATTiny13A that costs $0.35 and is available in SOIC8 and DIP8.

I needed to generate a 5V PWM output to drive a MOSFET for programmable closed-loop control of the speed of two types of DC motors in a very tiny space. There aren’t that many *really* small micro-controllers in packages that are reasonable to prototype with (I hate prototyping with QFN and BGA packages). I considered a few including the Microchip PIC10F322 (also SOT23-6) and the STM8 series (supports the great STLink debug environment). I eventually counted out the PIC because the development environment was so unfriendly (I’m done with expensive proprietary compilers) and counted out the STM8 because even though I’m quite experienced with the STM32, getting the peripherals programmed properly can be complex and I needed a solution fast, so I chose the ATTiny.

I used avr-gcc as the C compiler which is fast, familiar, and generates tight code (you can’t go wrong with gcc). Microchip has breadboard-friendly DIP-8 versions of the ATtiny13A and the pin-compatible ATTiny25/45/85, so I could rapidly prototype a solution. The documentation is excellent, the peripheral set is rich and easy to use (unlike ST uCs which are incredibly flexible but accordingly complex). It was so easy that I was able to get the code fully functional in just a few hours having never use AVR processors before. I understand you can even use Arduino to program it (I didn’t).

Useful tools:

Some notes on flashing tools. The Atmel-ICE is an awesome debugger that uses only the RESET line to do all of its debugging! Unfortunately it doesn’t supply power so it’s a lousy tool for flashing the target. I haven’t found the perfect tool yet, but the TinyAVR and USBasp (see links above) work well. The main down-sides are that they don’t have enclosures and getting them set up can be annoying; you need to install Zadig and reconfigure them to use libusb-win32 (see instructions here)…after that, they work well.

It’s not going to replace the STM32 family for most of my applications, and the STM8 series is arguably better, but for those times I need a really cheap, really small solution, the ATtiny is a nice addition to the toolbox. You can even order them from Digikey with your software pre-installed for an additional ~$0.25/chip making them truly a custom hardware component!

Some useful links:

Mustool == Junk?

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This is my second post about disappointing Mustool products (there won’t be a third).

I use stereo optical microscopes when doing surface-mount electronics (SMT) assembly and inspection. They work well, but are large and heavy. I decided to try one of the inexpensive “digital microscopes” that was reviewed well and looked like it had a large relief distance (the distance between the lens of the microscope and the item being viewed) which is important so you have room to work.  I ordered the Mustool G600 from Banggood.

Mustool G600

The good: the aluminum stand was easy to assemble and they even included the required Allen key.  The stand works well, adjusting the microscope height is smooth, and the relief is indeed quite good.  When I first turned it on, the buttons were a little unresponsive and it presented a menu that I couldn’t navigate, but after turning it off and back on, and adjusting the smooth focus knob, the microscope gave a clear, sharp picture.

Small bad: I didn’t realize how beneficial stereo is to SMT work.  With a mono image, even though it was sharp, I didn’t have any depth perception which made it hard to tell how high above the board my soldering iron and solder were.  It’s possible I’d get used to this but I’ll never know because…

Big bad: I played with the microscope for 5-10 minutes and then turned it off.  When I tried to turn it back on…nada: just a black screen.  I tried charging it, resetting it, pressing every button combo I could think of and it just remains unresponsive.  So it’s dead.

The worst: I received the package during the week and didn’t have time to play with it until the weekend which was past the Banggood 3-day warranty period – yes, you read that correctly: 3 days.  So any money I saved by purchasing on bangood is now easily offset by the $42 wasted on this piece of junk – not to mention the time and aggravation.

This is my second extremely disappointing mustool purchase; the first was their MT8205 scopemeter – which was also a complete waste and you can read about it in my blog. I will not purchase anything made by Mustool again; fool me twice…shame on me.

Until now, I’ve been a big advocate of banggood; they refunded my purchase price for the MT8205 – which reinforced my faith in them as a seller.  It’s a shame they are now carrying such junky products and chasing them with a ridiculous warranty.  I’m going to have to re-think purchasing from Banggood since the same products are usually available on amazon with reasonable warranty and return policies.

MT8205 review – piece of junk

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I’m always looking for bargain test equipment, and sometimes I get burnt; hopefully this review saves you from wasting some time and money.

I bought the Mustool MT8205 from Banggood who advertise it as a “2 in 1 Digital Intelligent Handheld Storage Oscilloscope Multimeter AC/DC Current Voltage Resistance Frequency Diode Tester”; it sells for just under $50 shipped.  I love Banggood and have had lots of good experiences with them, but buyer beware: this product is a waste of money at any price.  (Update: Although this product is something to avoid, Banggood is wonderful and I highly recommend them.  They took this product back at their cost just because I was unhappy with it…now that’s great customer service!)

Mustool MT8205

While it looks good, feels solid, and comes with nice probes and case, it simply isn’t useful for making measurements as my tests below will show.

Let’s start with how it works as an oscilloscope since that’s the interesting feature of this device.  When I ordered it, the ad said 200ksps which would suggest it is useful to look at signals up to at least 20kHz…not great, but at good enough for looking at audio and PWM waveforms.  However, as the ad now says, the analog bandwidth is limited to 10kHz.  A 15kHz signal is severely distorted and it won’t even try 20kHz.  A 10kHz ramp looks just like a 10kHz sinewave.  See the pictures below where I feed it a 15kHz sinewave and a 20kHz sinewave from a Rigol signal generator showing that the bandwidth is indeed limited to 10kHz (i.e. useless).  There are other issues too: there is no trigger control, the signal is always AC-coupled (so you can’t measure anything DC), there are none of the controls you’d expect to find on an oscilloscope and it’s too slow for virtually anything these days.  The scope feature is a complete bust.

To add insult to injury, the multimeter functionality is useless too!  The readout is only 3 digits and even those aren’t accurate!  I hooked the meter up to a lab voltage standard and checked the output with a calibrated 7-digit HP bench meter.  The 10.0000V standard was dead on with the HP meter, but read 9.95v on the Mustool.  What’s worse, when I used it to measure 2.5v and then used it to measure 10v again, it took several (I’m talking 4-5) seconds for the readout to gradually climb to 9.95.  Useless.

Summary:

  • Large/heavy/manual-ranging multimeter
  • Only 3 digits, only 2 of which are accurate (see 10vdc lab standard)
  • Incredibly slow: takes several seconds for voltage to read properly
  • Limited to 10kHz analog bandwidth
  • AC coupled only
  • Oscilloscope has no controls so not even useful as a teaching tool

10VDC from Lab Standard

15kHz sinewave

20kHz sinewave

Frequency Counters

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Although less exotic than the SA and VNA tools I use during development, I find I make use of basic frequency counters pretty often (mainly to calibrate equipment).

A frequency counter does only one thing: measures the frequency of an RF signal.  What’s important for a good counter is frequency range, timebase accuracy, speed of measurement, and of course cost.  I try to only purchase counters with an OCXO frequency standard although a good TCXO is often sufficient.  An external reference input is very useful when you need very high precision so you can slave the counter to a higher accuracy lab frequency standard (OCXO, GPSDO, or Rubidium).

Having had quite a few counters, I’ve concluded that if you need more than ~200MHz, the older HP/Agilent counters offer the best value, especially if you’re willing to spend $200-250 on eBay for one with their excellent OCXO timebase option (4).  If you aren’t buying a counter with an OCXO, I would make sure to get one with an external 10MHz reference input so you can slave it to an external high-accuracy standard.  If a counter isn’t accurate, what good is it?

I have a couple of HP5385A counters that work to 1GHz; one has the TCXO timebase and is quite accurate; the other has the superior OCXO timebase; both are excellent.  I also have an HP 5386A with OCXO that is good to 3GHz.  For higher frequency measurements, I have an HP 5347A that integrates a power meter and frequency counter up to 20GHz, its maximum frequency resolution is 1Hz (plenty for higher frequency measurements); it only has a TCXO timebase so I almost always use it with an OCXO or rubidium lab standard; it is larger/heavier than the other counters, but it’s hard to get an affordable counter with that much bandwidth.

For counters that are no longer officially in calibration (per certificate), I use a Trimble Thunderbolt GPS-disciplined oscillator (GPSDO) to calibrate them annually.

Recently, many companies have started adding bonus frequency counter functionality to their arbitrary waveform generators; for example, my SDG2042X has a counter input that is good to 200MHz.  The counter’s internal reference is better than 2ppm, but it supports an external 10MHz reference so I slave it to an external DOCXO standard for higher accuracy.  It requires around -10dBm (200mV) at 200MHz, less at lower frequencies: -20dBm (63mV) works at 35MHz.  Overall, it does quite well up to 200MHz and has some nice features lacking in older counters such as min/avg/max and sdev, duty cycle reporting, deviation from a reference in ppm, etc.

Pocket Multimeter

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During robotics season, I carry a multimeter in my backpack and as much as I love the UNI-T meters, weight and size start to matter when you carry something all the time so I wanted a smaller, lighter multimeter that still offered full functionality.  In my car, I keep an old Triplett 2030-C which has served me well over many years; the Aneng AN8203 is a knock-off that can be had for under $10 on AliExpress; both have frequency and duty cycle measurement (important for looking at PWM signals in robotics) along with the standard voltage/resistance/continuity and capacitance…but the Aneng has no current measurement where the Triplett does (however the scale isn’t useful for robotics).

Handheld O’Scope

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Owon USB scopes are great and I carry one in my robotics bag, but they aren’t ideal for field use because they take too much time and space to setup (laptop, wires, …).  So I purchased a the low-cost JinHan handheld oscilloscope and so far, I’ve been pleasantly surprised.  I bought the JDS2023 on AliExpress for $113 shipped via DHL (quickly); it integrates a 200MS/s dual channel 20MHz digital o’scope with a 5MHz signal generator in a remarkably small, light package.  It has a bright, readable 3.2″ LCD color display and a reasonably intuitive UI (I never needed the manual) although the addition of even a single knob would make the UI better.  It offers all the basic scope functions including automatic frequency and p-p amplitude measurements.  The Auto button does its job well.

JINHAN JDS2023 20MHz 200MSa/s Handheld Oscilloscope with Signal Generator

The company makes several models with a variety of speeds and features such as the JDS2012A that integrate a scope and multimeter.  However, I prefer to keep carrying my UT136B meter which is smaller, easier, more functional (as a meter), and cheap enough that I won’t care when students lose or destroy it.  For advanced diagnostics or impromptu demonstrations, the JDS2023 will replace the Owon USB scope in my robotics bag

EEVBlog does a teardown of the JDS2012a.  The user manual is here.

The scope comes well packaged and includes a single 6100 (ostensibly 100MHz) scope probe, BNC to alligator-clips cable for the signal generator, USB cable, and separate battery charger.  It does not include the required 18650 lithium battery (probably due to air shipping restrictions) or a carrying case…but what do you expect for $113?  Power over the USB cable will run the scope.

I haven’t seen anything close to this level of functionality at this price.  If I need more, I’ll probably step up to the Owon HDS1021M-N or UNI-T UTD1025CL, but they are twice the price, considerably larger, and sans signal generator.

I tested it quickly using a lab-grade RF signal generator and confirmed the 20MHz bandwidth specification; it clearly shows at least 10 points per cycle of the sinewave (validating the 200MS/s specification) and there is no amplitude compression of the 0dBm signal (nominally 0.632vpp into a 50-ohm load – this is unloaded so it correctly shows 2x vpp); the analog front end 3dB compression point is somewhere north of 40MHz.

20MHz Sine Wave

5MHz Sine Wave

Feeltech FY3200S Signal Generator

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Update 8/3/2017:

It looks like there’s a new low-cost signal generator option that appears significantly better than the Feeltech.  The Ruideng JDS6600 comes in version from 15MHz ($78) – 60MHz ($122) and has a control panel that is much nicer; more like the Rigol and Siglent low-end signal generators but at a significantly lower price point.  I haven’t tried these yet, but next time I’m buying an inexpensive signal generator, that will be the one.

Update 5/4/2016:

I replaced the AC power jack with a 3-prong jack and connected the earth/safety ground to the DC ground and now the DC ground is (of course), at earth/safety ground potential and there is no unwanted/unexpected AC voltage on the outputs so I am once again pleased with this signal generator/frequency counter.   The cost of the replacement jack is low

Update 4/23/2016:
I’ve ordered a 3-conductor AC socket that was suggested as an easy-to-fit replacement  for the 2-condoctor socket on the FY3224S; the socket is available from amazon and ebay (note: both are very slow shipping).  When it arrives, I’ll replace the existing AC socket and connect the DC ground to AC safety/earth ground.  I’d rather have the output truly float, but I think this is an acceptable solution.

Update 3/10/2016:

I got a mild shock from my FY3224S today; the problem appears to be with the mains filter implementation.  Measuring between the BNC connectors (DC ground) and the AC earth ground I see an 82v peak-to-peak signal.  For more information see eevblog here.  The signal is low current when the unit is on (around 32uA) which is well below the 250uA limit for such gear.  There’s 110vac at around 50uA on the DC ground (the exposed metal connectors) when the unit is off.  I think this is not dangerous, but it’s nothing I’d want to connect to the sensitive circuits I’d use a signal generator to feed.  The issue is that the power supply is Class II (no earth ground) and there’s an EMC reduction capacitor that bridges the HV and SELV sides of the transformer.  AC current leaks through this capacitor to the DC output connectors.  From my perspective this is unacceptable for electronic test equipment as it could easily damage whatever it is connected to if that equipment is earth referenced.  Until this is resolved, I can’t use or recommend this signal generator to anyone.

——————————————————

I wanted a second signal/function generator to use at home and couldn’t resist buying a Feeltech FY3200S.  They are commonly available for under $80 shipped on eBay and claim to generate waveforms at up to 24MHz.  It arrived today and I did a quick head-to-head comparison between it and my Rigol DG1022 signal generator.  The Rigol is a 25MHz generator and I’ll say up front that it is a joy to use and looks and feels like a real piece of lab equipment; however it also costs nearly 5x as much as the Feeltech.

The FY3200S is a DDS generator with a claimed 250MS/s rate so it

FY3200 Signal Generator

FY3200 Signal Generator

should do a serviceable job of generating sine waves at up to 24MHz (I consider 10 points per cycle the minimum).  The FY3200S lets you control the waveform either from your computer using software and a standard USB A-B cable or via a front panel with 2-line LCD display, several membrane buttons and a rotary encoder (dial).  Interaction is straightforward, but clunky compared to the Rigol.  Unfortunately the USB cable does not power the generator.  You must power the generator via its 2-conductor AC cable (universal 85v-260vac).

I have been disappointed by other low cost DDS generators, particularly at higher frequencies.  Because it is DDS, I expect good frequency accuracy (which it has).  The big questions in such a low cost device are waveform stability (jitter) and how the analog output stage performs at higher frequencies.  So I ran a few tests to see when the analog output would fall apart.  The output was connected to my Rigol DS1052 (50MHz hacked to 100MHz) oscilloscope so there was no load on the generator (I’ll test again with a 50-ohm load later).

I also tested the software that lets you control the generator via USB from your computer and it worked well.

The FY3224S includes a frequency counter rated for 100MHz.  Depending on the signal level, mine was able to measure signals accurately up to 225MHz (at +13dBm) which was pretty impressive for a device this inexpensive.

On to the tests: I configured the generator for a 1kHz 1v sine wave and gradually raised the frequency while observing the amplitude.  As you can see, it held together nicely through about 3MHz and then started to drop.  Clearly the GBW of the output buffer (likely a low cost op-amp) is not sufficient for the higher frequencies; I’ll probably open it up later to see if it can be replaced with a better op-amp.  Looking only at frequencies above 1MHz:
1MHz = 1v03
2MHz = 1v01
3MHz = 0v98
5MHz = 0v86
10MHz = 0v59
15MHz = 0v42
20MHz = 0v29
24MHz = 0v21
Stability and shape of the sine wave was good across the entire range of frequencies.  At higher frequencies, the digital steps were clear as jaggies in the signal; the output filter could provide better smoothing, but overall it was pretty good…not as good as the Rigol, but still decent.  I need to run some more tests with the output connected to a spectrum analyzer.

FY3200S 1KHz 1V Sine

FY3200S 1KHz 1V Sine

FY3200S 10KHz 1V Sine

FY3200S 10KHz 1V Sine

FY3200S 100KHz 1V Sine

FY3200S 100KHz 1V Sine

FY3200S 500KHz 1V Sine

FY3200S 500KHz 1V Sine

FY3200S 1MHz 1V Sine

FY3200S 1MHz 1V Sine

FY3200S 2MHz 1V Sine

FY3200S 2MHz 1V Sine

FY3200S 3MHz 1V Sine

FY3200S 3MHz 1V Sine

FY3200S 5MHz 1V Sine

FY3200S 5MHz 1V Sine

FY3200S 10MHz 1V Sine

FY3200S 10MHz 1V Sine

FY3200S 15MHz 1V Sine

FY3200S 15MHz 1V Sine

FY3200S 20MHz 1V Sine

FY3200S 20MHz 1V Sine

FY3200S 24MHz 1V Sine

FY3200S 24MHz 1V Sine

The next challenge was square waves.  I was pleasantly surprised to see a decent 1MHz square waveform and even at 5MHz, it wasn’t too horrible.  At frequencies much above 5MHz, the square edges were mostly gone, especially at higher voltages (see the difference between a 5vp-p square wave and 1v p-p square wave at 10MHz below); this again suggests an analog output stage limitation (op-amp with insufficient slew rate).  Regardless of the amplitude setting, there was a *lot* of jitter at higher frequencies which is certainly not an output stage problem.  Duty cycle control worked as expected.

FY3200S 5MHz 5V Square Wave

FY3200S 5MHz 5V Square Wave

FY3200S 1MHz 5V Square Wave

FY3200S 1MHz 5V Square Wave

FY3200S 5MHz 5V Square Wave

FY3200S 5MHz 5V Square Wave

FY3200S 10MHz 5V Square Wave

FY3200S 10MHz 5V Square Wave

FY3200S_10MHz_Sqr_Jitter

FY3200S 10MHz 1V Square Wave Jitter

FY3200S Duty Cycle

FY3200S Duty Cycle

FY3200S 1MHz 5V 25% Duty Square Wave

FY3200S 1MHz 5V 25% Duty Square Wave

FY3200S 1MHz 5V 25% Duty Square Wave

FY3200S 1MHz 5V 25% Duty Square Wave

I thought it would be interesting to compare the results with a Rigol DG1022U set to generate a 5v sine wave (yes, I know I should have used a 1v sine wave).
1MHz = 5v12
5MHz = 4v44  (88% of nominal vs. FY3200S: 86%)
10MHz = 3v28 (66% vs. 59%)
15MHz = 2v52 (50% vs. 42%)
20MHz = 1v92 (38% vs. 29%)
24MHz = 1v68 (34% vs. 21%)

Rigol_DG1022U

Rigol_DG1022U

DG1022U_1KHz_5V_Sine

DG1022U_1KHz_5V_Sine

DG1022U_1MHz_5V_Sine

DG1022U_1MHz_5V_Sine

DG1022U_5MHz_5V_Sine

DG1022U_5MHz_5V_Sine

DG1022U_10MHz_5V_Sine

DG1022U_10MHz_5V_Sine

DG1022U_15MHz_5V_Sine

DG1022U_15MHz_5V_Sine

DG1022U_20MHz_5V_Sine

DG1022U_20MHz_5V_Sine

DG1022U_24MHz_5V_Sine

DG1022U_24MHz_5V_Sine

DG1022U_1MHz_5V_Sqr

DG1022U_1MHz_5V_Sqr

DG1022U_2MHz_5V_Sqr

DG1022U_2MHz_5V_Sqr

DG1022U_5MHz_5V_Sqr

DG1022U_5MHz_5V_Sqr

DG1022U_1MHz_Sqr_Edge

DG1022U_1MHz_Sqr_Edge

I ran several tests of the frequency counter to try to find its limits.  It met the 100MHz spec at +7dBm signal strength and actually reached 225MHz at +13dBm (the limit of my generator).  My source was a Marconi/IFR RF signal generator.  The test results were:
-5dBm: 6MHz
0dBm: 47MHz100MHz: +7dBm
+13dBm: 225MHz

Signal Generator 6MHz

Signal Generator 6MHz

FY3200S_6MHz_Neg5dBm

FY3200S_6MHz_Neg5dBm

Signal Generator 47MHz

Signal Generator 47MHz

FY3200S 47MHz 0dBm

FY3200S 47MHz 0dBm

Signal Generator 100MHz

Signal Generator 100MHz

FY3200S 100MHz 7dBm

FY3200S 100MHz 7dBm

Signal Generator 225MHz

Signal Generator 225MHz

FY3200S_225MHz

FY3200S_225MHz

Finally I wanted to look at the spectral purity of the generator; I used an Anritsu MS8609A spectrum analyzer to examine 1V sine waves at 100kHz, 10MHz, and 24MHz.  I examined close-in spurs that are typically modulation caused by noise in the power supply and harmonics to see how well the analog output filter works.  I’ve also included a few pics of the output of a high quality RF signal generator (Marconi/Aeroflex IFR2025) for comparison.  Overall, the Feeltech generator did better than I’d expected.

FY3200S 100kHz 1V sine harmonics

FY3200S 100kHz 1V sine harmonics

FY3200 10MHz sine spurs

FY3200 10MHz sine spurs

FY3200S 24MHz sine wave harmonics

FY3200S 24MHz sine wave harmonics

IFR2025 10MHz sine spurs

IFR2025 10MHz sine spurs

IFR2025 24MHz Harmonics

IFR2025 24MHz Harmonics

My conclusion so far is that while the Feeltech it is not as good a signal generator as the Rigol (no big surprise here…it’s less than 1/4 the cost), but in terms of output quality and capabilities, it comes pretty close and for many applications, it is quite usable and appears to be an excellent value.  The frequency counter is a nice bonus!

If time permits, I’ll tear it down and look at the output stage and timebase to see if any improvements can be made.

Owon VDS1022

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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!

RF Test Gear

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Most of the RF work I do is in the 902-928MHz ISM band.  I have lots of RF test gear, but concluded that I really only need a few pieces and found that great bargains can be had by purchasing and re-purposing surplus cellular test equipment on eBay.  Some cellular gear includes general purpose RF test capability and this has allowed me to equip my lab at a tiny fraction of the cost of comparable new general purpose equipment:

  • Aug 2023
    I bought a Siglent SSA3021X+: which is a modern, compact 2.1GHz spectrum analyzer+TG that is easily hacked to become an SVA1032X (the same hardware platform running different software). The hack expands the BW to 3.2GHz, adds VNA (S11, S21) capability, and enables all options. The SpecAn covers 9kHz to 3.2GHz, VNA=100kHz to 3.2GHz, 0.7dBm amplitude accuracy, 1ppm reference, -98dBc/Hz PN, -161dBm/Hz DANL, and generally decent specs with a modern user interface. Costs around $1650 from TEquipment (whom I highly recommend).
  • Oct 2020:
    small gear that I can use at my desk often gets more use than fancy lab gear that takes up too much space.  I bought a TPI-1005 RF USB-powered signal generator/analyzer and love it.  What distinguishes this from the toy signal generators widely found from China is that it is calibrated and accurate.  What distinguishes it from lab gear is harmonic suppression (or lack thereof).  However, it is an incredibly handy tool, compact, and reasonably inexpensive.  You can generate signals on frequency with precise amplitude, measure signal strength, and sweep antennas and filters.
    Oddly, the device comes with two (rarely used) push-buttons without caps.  The caps can be ordered very inexpensively from Digikey, Mouser, etc.: Wurth 714651010100, 714656010100.
  • Feb 2016:
    An Anritsu MT8222A (see datasheet).  Is meant for cellular base station service, but it includes an even richer set of features than my prior favorite cellular test tool, the Agilent E7495.  Most importantly, the MT8222A includes VNA capability!  It also provides a spectrum analyzer that covers 100kHz through 7.1GHz with decent specs (PN = -100dBc/Hz, 1.25dB amplitude accuracy without PSN50, 1ppm reference). It provides a broad set of 1 and 2-port swept gain/loss analysis tools for cable and antenna analysis from 10MHz-4GHz.  It is significantly smaller and much lighter than the HP/Agilent E7495A and the battery works!  At some point I need to try it with Anritsu Handheld Software Tools or Master Software Tools. I use it with an Anritsu PSN50 power sensor (50MHz-6GHz) for high accuracy (0.16dB) measurements (see datasheet).  Unfortunately it has no CW/AM/FM/FSK signal generation capability although obviously the hardware is capable, but probably not in a leveled way.
  • Anritsu MS8609A – 13GHz RF Spectrum Analyzer
    A lab-grade 10GHz spectrum analyzer is needed to measure harmonic compliance prior to FCC testing.  I use an Anritsu MS8609A (13+GHz) which is not quite as good as the best HP gear, but is fairly modern and more than good enough for my needs; it includes a bonus power meter.  Mine has a rubidium frequency standard too so I can slave my other gear when high frequency accuracy is needed.  See the datasheet.
  • Marconi/Aeroflex/IFR 2025 – 2.5GHz RF signal generator
    Generates pretty clean RF signals with analog modulation.  Not HP quality, but still plenty good and more than meets my needs.  It is a pleasure to use. See the datasheet and  manual.

Hobby-grade RF Tools
Hobby-grade RF tools have gotten a *LOT* better over the last 5 years. I had earlier versions of these and they were marginally useful…more toy than tool, but their quality has improved steadily and these RF essentials (SA, VNA) are now useful as tools and an amazing value for a little over $100 each; they make RF design much more accessible to hobbyists.

  • Tiny SA Ultra (100kHz – 5.3GHz) spectrum analyzer (V 0.4.5.1)
    Yep, a 5GHz spectrum analyzer with bonus signal generator for under $150. Crazy!
    Specs are getting decent too: PN is now -92dBc/Hz, 2dB amplitude accuracy, leveled signal generator provides CW, and also AM and FM modulation. See the wiki. Some important limitations: 200Hz min RBW, the SigGen cannot serve as a tracking generator for the SA. See links here. and the developer’s youtube videos here which include honest assessments of the limitations and how to work around them. This video describes the ultra and its limitations. It’s most useful when you limit the signal level into it using a fixed attenuator.
  • NanoVNA SAA-2N (V2_2) 50kHz-3GHz – surprisingly accurate; also almost out of the toy category. Due to its size and battery operation, it is often what I grab to do a quick sweep of an antenna. The manual, firmware, VNA Qt PC software, etc. are here. $110 for a VNA…

  • I’ve also added a separate page on the frequency counters I use, however I rarely use counters these days. Most of what I need to measure is under 100MHz and for convenience, I just use the counter built into the SDG2042X signal generator which is already on my desk; when slaved to an external 10MHz DOCXO standard, it is quite accurate.

BG7TBL USB RF Signal Generator

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Some time ago, I purchased a super-cheap RF signal generator on eBay from fly_xy.  It was the same as this item.  This is yet another version of the the popular BG7TBL signal generator and “simple spectrum analyzer”.   It cost $65 and covers 138MHz through 4.4G; for another $20, you can get one that goes down to 35MHz.  It’s certainly not lab gear, but for the price and size, it’s still decent; the main challenges are the software and the resolution bandwidth.

USB RF Signal Generator

Harmonics are not attenuated; with the generator configured to output a 915Mhz CW signal, the fundamental lands at 914.993Mhz @ -5dBm signal (7ppm error), pretty clean to -40 to -50dBm, acceptable to -70dBm.  However the harmonics are ugly: 3rd = -13dBm, 4th = -24dBm, 5th = -36dBm, 6th = -48dBm, etc.

Inside are:

  • AD8307 500MHz demodulating log amp
  • AD4350 RF synthesizer
  • IAM 81008 Mixer
  • ATMega processor
  • FTDI FT232RL USB to serial interface
  • AMS1117 super cheap LDO

A review (translated from Polish) that measures harmonics and frequency accuracy and such:  http://sztormik.com/Radio/Wpisy/2014/10/1_BG7TBL_measurements_files/bg7tbl_lo_meas.pdf

It would be *much* more useful with selectable RBW filters; as it is, I can’t resolve much detail finer than 200kHz, so an FM signal with 25kHz deviation will look the same as an FM signal with 100kHz deviation.  See the pictures below for some sweeps of the 2m band.  The NWT4000 or NWT4000-2 might be more capable (but they are sufficiently more expensive that it would be better to buy a real piece of lab gear like a used R&S CMU200 – even though it is admittedly much larger).

Sweep of 2m band

2m band

Close-up of signal in 2m band

The software it uses is open-source LinNWT / WinNWT which supports many similar devices.  The English language documentation is not great and because the native language is German, there’s not much English language support.  A German magazine article is here it looks like it would be very useful if translated into English.  The author (Andreas) is friendly and helpful and responds to email.

To run WinNWT in English on windows, use the command (in the Target field of the shortcut properties):

“C:\Program Files (x86)\AFU\WinNWT4\winnwt4.exe” app_en.qm

To build/run the software on linux:

  • Download latest .tgz source here
  • Install tools if needed: sudo apt-get install gcc qt4-qmake libqt4-dev
  • tar xzvf linnwt_X_Y_Z.tar.gz
  • cd linnwt_X_Y_Z
  • qmake-qt4
  • make
  • If you want to make it available system wide: sudo cp linnwt /usr/local/bin/linnwt
  • sudo linnwt app_en.qm

To use the software, I configure Settings->Options->StartFrequency=80000000, StopFrequency=100000000, DDS clock=400000000, Interface=/dev/ttyUSB0 on linux or COMx on windows, max.Sweep=200000000, frequency multiply=10.  Then in the Sweepmode tab, to monitor the ISM band, configure StartFreq 902000000, StopFreq=928000000, Samples=1000 and press Continuous to sweep continuously; press Stop to stop sweeping.  This results in 26kHz steps.

I also bought the BG7TBL “tracking” (i.e. broadband) noise source in the hope of being able to do some basic antenna return loss/swr measurements; it does generate broadband noise at around -40dBm, but so far I’ve had no luck using it with the “simple spectrum analyzer” and a return loss bridge to sweep an antenna.
noise_source

Links:
https://www.facebook.com/media/set/?set=oa.809669625718111&type=1
http://ea4eoz.blogspot.com/2014/07/modifying-bg7tbl-noise-source.html
http://ea4eoz.blogspot.com/2014/07/installing-bg7tbl-noise-source-as-poors.html
http://www.mikrocontroller.net/topic/336482 (English Translation)
http://cas.web.cern.ch/cas/Germany2009/Lectures/PDF-Web/Caspers.pdf
http://bg7tbl.taobao.com/  (English Translation)
https://vma-satellite.blogspot.com/2019/04/new-simple-spectrum-analyzer-device.html (newer D6 version)
https://www.rudiswiki.de/wiki9/SpectrumAnalyzer_LTDZ#Links (newer LTDZ version)
http://alloza.eu/david/WordPress3/?page_id=478 (SNASharp software)