EEVblog #5 – Instek Function Generator ReviewPosted on April 24th, 2009 9 comments
Maxim rant, Analog Microchip, Instek Function Gen Review
Dude, the video blog is a great idea. I just added it to my RSS feeds so I can catch them all
Hey Dave, Great podcast, keep it up.
Why don’t you tell us about some specific analog chips from Microchip and why you like them over others?
How about letting us know about your day job? Where do you work, or at least what kind of stuff you do?
Just found your video blog mentioned on the Makezine.com blog. I watched this post and wanted to subscribe via iTunes but it told me that it wasn’t available in the US store, bummer. Anyway nice job, keep up the good work.
I’ve just added iTunes podcasting support, it may take a day or two to update. Please try again.
Great idea Dave we all needed a blog like this!!
I think the equipment review is great, I have just started to collect tools and equipment for a home based lab and I wouldn’t mind if you did some more reviews on older equipment that maybe are a de facto/industry standard that won’t break the bank and also are repairable, which looks like that is a concern of yours anyway. I am in the middle of my EE education and would like my own test equipment, I could do a bit of googleing buy your years of experience mean a lot more.
Thanks and keep it up, much appreciated experienced and real world insight.
Nice video this time around. That function generator is the exact one we use at school (I attend classes for Electronic Engineering Technician stuff, so not as in-depth as EE, but with lots of hands-on-equipment time), and it works pretty well, albeit with a limited output frequency. Also, if you need any signal below about 12mVpp, you’re out of luck (even with the ATT -20dB button pressed and the amplitude knob pulled out). Otherwise, pretty good equipment.
Well, for me the main downside of this generator (actually a downside of many Instek generators) is that the amplitude knob is too near from the BNC socket! Think about such a situation: you want -20dB so you pull out the knob. After some time you want to change the cable so you have to manipulate on the socket and it is possible you push the knob in accidentally!
I think the instability problem on the Instek may be a case of operator error and real world potentiometer limitations. This unit probably has 1000:1 tuning range on the frequency knob which you should avoid using instead of the decade switches when you need stability but can be handy for doing a quick sweep.
The first thing that struck me about the instek function generator was the part number. I have, from the early 1980s, an Elenco GFG-8016D function generator. Interesting similarity in part numbering. The 8016D is, of course an old model. Similar case, analog function generator with counter, but the instek looks like a newer design with non-latching switches and different front panel layout. I think it cost about $80 back then and I have gotten good use out of it.
After two or three decades:
– The plastic case recently failed the 2 meter drop test, but nothing a little tape can’t “fix”.
– IIRC, Some of the little pots (like amplitude and centering) are a little scratchy and need to be wiped back and forth before use. Frequncy
– The frequency knob has lost its center calibration and has reduced span to just under a decade – some pots inside probably need to be tweaked. There is a tweaky pot in series that probably needs adjusting. But still good frequency correspondence between decades.
– stability is +/- 1 count, even on the low end.
– the manual, including schematics and service info, is available on the web site.
The frequency knob is graduated from 0.2 to 2.0 times the selected decade with an ungraduated range beyond that at each end. On the low end, you can go way down. Which means it was originally possible to produce the same frequency on more than one combination of decade switches and knob position. But it is better to use the nominal combination.
Looking at the schematics, I see the Elenco is made by Good Will Instrument Co, the same people who make Instek.
Another Instek model, the GFG-8015 advertises a 1000:1 tuning range on the frequency knob which is constent with the original behavior of my generator.
Before the frequency pot lost its span, I seem to recall it had a little instability at the low end which was really an issue of operator error. If your frequency pot is just a bit scratchy and you are using the low end of the knob settings instead of setting the decade switch to the right position for the frequency you want to generate, then that would explain the instability. Suppose you have a 2.5K pot with 1 ohms of instability. It will work a lot better in the 1K ohm range (0.1%) than at the 10 ohm range (+/-10%). Just click up a decade or two.
Looking at the scehmatic, it looks like a 741 is used as a sawtooth oscillator and a diode shaping bridge (three bridge rectifiers with resitors) a non-linear transfer function that approximates a sine wave. A bit dodgy. There is probably some significant harmonic distortion.
Mine was a good deal for $80 decades ago. In inflation adjusted dollars, yours is still about $80, though most electronics has come down in price rather than going up. I think this unit is now way overpriced for decades old technology with a minor facelift. For a $300 chinese product, I expect a USB (TMC/SCPI) control port on the back as well as a front panel, arbitrary waveform synthesis, direct digital synthesis, sweep, modulation, an accurate timebase, two channel output (including I/Q), and software defined radio capabilities. The Rigol DG1022 ($549) would be closer. Real Soon Now, I would expect a USB 3.0 port so you can stream real arbitrary modulated data from a PC, such as ATSC video, and a heterodyne up converter, and several 10Mhz ADC channels for analog modulation (including RGB/YUV) feeding into the FPGA, and full disclosure of technical details so you can reprogram the damn thing.
While it is only DDS (not arbitrary) and apparently not USB controllable, the Instek SFG-1003 does everthing this one does (except sweep) for half the price; sweep and higher frequencies run the price up.
Hey Dave, I realise that this is an old entry but had a couple of questions, when you tested the unit for jitter and showed the results on the scope thats cool but did you try it with another scope? and did you try the scope in this test with another known working function generator? I ask because sometimes I have seen things futs which before seemed perfectly reasonable and think its always a good idea to double check the results…. Just in case… Just my 2c worth but this is a great blog and some of your later articles have helped in my selection of oscilloscope.
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