EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: h_p on April 19, 2017, 11:58:53 pm
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All,
I received a GFG-8219A function generator in the mail today that I bought off eBay. I fired it up and noted three things. One I randomly get noise on the positive going side of wave forms. The second issue I noted is that the frequency is difficult to set as the pot on mine seems to be incredibly touchy and it is difficult to stop on a specific frequency. I also noted that the frequency drifts after its set. I set it at 30Khz and it has now drifted down over the last 10-15 mins down to 29.978 Khz and is continuing to drift down. Does anyone know what is causing this and a fix for either of these issues? Or should I just return the unit and try my luck with another one? I am completely comfortable taking it apart and replacing parts if they are available. Much thanks in advance.
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The second issue I noted is that the frequency is difficult to set as the pot on mine seems to be incredibly touchy and it is difficult to stop on a specific frequency. I also noted that the frequency drifts after its set. I set it at 30Khz and it has now drifted down over the last 10-15 mins down to 29.978 Khz and is continuing to drift down. Does anyone know what is causing this and a fix for either of these issues?
Those things are, unfortunately, going to be par for the course for that thing. I had one at one time. It's just not a very good unit. The frequency you see is coming from a separate frequency counter, which has nothing whatsoever to do with the circuitry generating the output frequency, so you see drift from both the frequency counter and the main generating circuit. And yea setting any frequency above the kHz range is going to be frustrating if you want gnat's ass accuracy.
As for the noise, probably dirty pots if it's used or some other issue if it's not used. If these things are not making you happy then I'd ditch it and get something better. :)
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Well that's unfortunate. I figured it was something like that. It drifts on every single frequency you set it on. I have contacted the eBay seller I bought it from and have requested a refund. Any recommendations for a frequency counter around $100. I had heard good things about this one;
http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT)
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Any recommendations for a frequency counter around $100. I had heard good things about this one ...
Well, I have champagne tastes in such things so I can't really recommend one for $100, but I'm sure we can get someone to help you in due time. :)
Edit: I do like very much your member name. A name that truly represents quality to me and many other folks.
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I fully understand that. When I was in the Navy I was responsible for all the test equipment on my Destroyer (I was an Electronics Technician for 10 years). I really miss having a lot of that gear now as a civilian. But I can't afford to spend more than that and I really don't need anything fancy. But finicky pots and not staying on frequency will drive me absolutely insane. So back to the seller it will go.
Thanks for the complement on the user name. HP used to make great stuff. I just picked up some HP E3610 power supplies. H and P are my initials I didn't really put any thought in to it.
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Well that's unfortunate. I figured it was something like that. It drifts on every single frequency you set it on. I have contacted the eBay seller I bought it from and have requested a refund. Any recommendations for a frequency counter around $100. I had heard good things about this one;
http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT)
I'd go for a Feeltech FY3200 series like this one:
http://www.ebay.com/itm/FeelTech-6-24M-CNC-Dual-CH-DDS-Function-Signal-Generator-Sweep-Frequency-Counter-/361838640709 (http://www.ebay.com/itm/FeelTech-6-24M-CNC-Dual-CH-DDS-Function-Signal-Generator-Sweep-Frequency-Counter-/361838640709)
Do change the AC inlet for one with a ground pin connected to the 0V at the secondary side of the PSU.
The function generator you have is an RC oscillator and it will never be really stable. I also have one like that from Voltcraft and I don't even dare to sell it. I'm afraid getting a refund will be hard because the generator you bought works as it should.
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I'm a little leery about buying that Function generator, especially after watching this review.
https://www.youtube.com/watch?v=9o5MzTOzZo4 (https://www.youtube.com/watch?v=9o5MzTOzZo4)
I have a feeling this one will work better.
http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/261114462307?_trksid=p2060353.m1438.l2649&var=560163970489&ssPageName=STRK%3AMEBIDX%3AIT)
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Edit: I do like very much your member name. A name that truly represents quality to me and many other folks.
HP = High Priced :)
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Edit: I do like very much your member name. A name that truly represents quality to me and many other folks.
HP = High Priced :)
For a good reason ... :)
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I'm a little leery about buying that Function generator, especially after watching this review.
https://www.youtube.com/watch?v=9o5MzTOzZo4 (https://www.youtube.com/watch?v=9o5MzTOzZo4)
If you ground the PSU output on the Feeltech generator then all is well. IMHO it is total overkill to put a linear supply in this generator. There is a whole thread about it: www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/ (https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/)
Besides that the adapter which comes with the Ascel generator is likely to have the same floating ground problem. Having two outputs can be handy from time to time which is also something the Ascel generator is missing.
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I thought about what you said and I began looking at better switching PSU's before you mentioned the grounding. I found a much higher quality PSU (with a ground) for $30 on digikey. Then I could swap out that figure 8 connector on the back with a IEC320-14 connector and ground it. I am unsure if the current output of this PS is adequate as I haven't really found that info for the FeelTech.
https://www.digikey.com/products/en?keywords=271-2531-ND (https://www.digikey.com/products/en?keywords=271-2531-ND)
https://www.digikey.com/product-detail/en/qualtek/703W-00-08/Q336-ND/1164207 (https://www.digikey.com/product-detail/en/qualtek/703W-00-08/Q336-ND/1164207)
What page of that thread does it describe the grounding that you are speaking of? I don't have the time at the moment to look through all 19 pages of that thread. Thank you.
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What page of that thread does it describe the grounding that you are speaking of? I don't have the time at the moment to look through all 19 pages of that thread. Thank you.
That modification is simple. In the one I have I fitted a grounded AC inlet and connected the earth pin to the 0V output of the power supply. If you open the unit it is pretty much self explaining.
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Thanks! I found one that goes up to 20Mhz used on eBay for $35. I will probably pick that one up. Then with the cost of the modifications it'll be around the same price as new!
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I've had one of these for years. I'm looking at it now. At the time I bought it it was the best function generator I could afford. It's always been hard to set, and has probably always drifted a bit. It was never really a great unit, but it did the job. Haven't had any noise problems that I can recall. Last year was able to afford to upgrade to a Siglent SDG2042X. A huge and satisfying improvement.
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Well I got a refund on it. I guess I am just too used to high precision electronics and test equipment at work. It was going to drive me nuts with it constantly drifting. I bought the FeelTech 20Mhz model I found on ebay for $35 and ordered a better switching power supply for it and a mains adapter with a ground. I'll post pics whenever I receive it and get it modified.
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Well that $35 function generator was a bust. It wouldn't create a square wave at all. If anyone has any recommendations on function generators I am all ears. :)
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Well that $35 function generator was a bust. It wouldn't create a square wave at all. If anyone has any recommendations on function generators I am all ears. :)
Outside your budget I know but have a look at SDG1032X, 30 MHz, 2 channel for $399, a $100 cheaper than the 2042X that's already been mentioned. Unlike the 2000X series the 1000X models can do square wave to the same frequency as sine wave. Otherwise they're just as capable albeit not frequency wise as the 2000X models.
http://siglentamerica.com/pdxx.aspx?id=4705&T=2&tid=16 (http://siglentamerica.com/pdxx.aspx?id=4705&T=2&tid=16)
There's threads for both these on the forum and not hard to find.
A member had a spare 2042X in the Buy/Sell board just a week or so back.
There's some member discount threads too where you can get a code to enter at online checkout for ~6% off the price.
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Well,
I solved the problem by buying a philips PM6666 counter and it works fantastic. If you are in the US shouldn't be a big problem to get a used unit.. I paid some money because it had the C option...
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I think I am going to save up and buy that Siglent. I can't stand how poorly these "cheap" units function due to having used nothing but quite expensive TE at work for almost 20 years.
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I think I am going to save up and buy that Siglent. I can't stand how poorly these "cheap" units function due to having used nothing but quite expensive TE at work for almost 20 years.
Better go for Keysight and Tektronix then because the Siglent generators also have their quirks!
Would you care to elaborate how you measured the square wave and what frequency you tried? You have to remember that a square wave consists of many higher harmonics so the output stage of a function generator needs to have a lot more bandwidth than for a sine wave. For that reason many function generators specify the maximum frequency for non-sine waveform shapes at less than 10 times the maximum sine wave frequency.
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I don't remember exactly but I started in the low Khz range and ran up to a few Mhz and there was nothing present but noise. I tried another function generator on the same scope (Rigol DS1054Z and a GFG-8219A) and while the frequencies drifts like a mofo on that thing there was no issue in creating a square wave until you reached it's limits and it began having noise on the leading edge of the waveforms.
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I don't remember exactly but I started in the low Khz range and ran up to a few Mhz and there was nothing present but noise. I tried another function generator on the same scope (Rigol DS1054Z and a GFG-8219A) and while the frequencies drifts like a mofo on that thing there was no issue in creating a square wave until you reached it's limits and it began having noise on the leading edge of the waveforms.
You wrote you got it used so chances are you got duped again and bought a broken unit. Here are some squarewave screendumps from my Feeltech FY3200S (6MHz version). If you got noise it could also be a problem in the cable you used (cables don't live forever).
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Oh yeah its definitely broken. The seller doesn't know anything about electronics. He is thankfully allowing me to return it.
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I think I am going to save up and buy that Siglent. I can't stand how poorly these "cheap" units function due to having used nothing but quite expensive TE at work for almost 20 years.
Here's a screenshot of SDG1032X @ 30 MHz square wave, one I grabbed for a customer inquiry only yesterday.
Check the rise time for this class of AWG. ;)
(https://www.eevblog.com/forum/testgear/gw-instek-gfg-8219a-function-generator/?action=dlattach;attach=310833)
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That rise time :(
1 microseconds compared to say a Fluke 271 with a rise time of 22 nanoseconds. It'll meet my needs though. Well or it'll drive me nuts.
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That rise time :(
1 microseconds compared to say a Fluke 271 with a rise time of 22 nanoseconds. It'll meet my needs though. Well or it'll drive me nuts.
Look again, 3.9 ns. DSO measurement agrees with datasheet spec.
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Whoops you are right. Spec is 3.8ns. I was looking at the wrong spec lol.
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Whoops you are right. Spec is 3.8ns. I was looking at the wrong spec lol.
Before I got into this game I thought my old Philips FG was the bees knees :-DD and now I've had a good play with most of Siglent's units and for an off the shelf unit that you don't want to hack the SDG1032X is becoming my favourite.
Sure, there are higher spec units available from A brand manufacturers but for what price ? :scared:
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For sure. $250 ish vs $1,700. I definitely don't have any issue for a unit that costs that much.