| Electronics > Beginners |
| Is this funtion generator junk? |
| (1/4) > >> |
| eswets:
I just purchased a Madell CA1640-20 function generator and right out the box, the frequency knob fell off. then I go to test the thing and in all different frequency ranges, the frequency changes after I set it. So if I start it at 2khz even, in about 45 second it will climb up to 2,010hz then down to 1990hz. Is this normal or junk? Here is the link: http://www.madelltech.com/m1-8.html So I don't need a top of the line generator, I just need one that I can play around with to help teach myself. Let me know if I should return this and if so what would you suggest for a $250-500 budget? Again I don't know much about these so I took a chance with this. I should have asked here before I bought. Thanks Eric |
| rossmoffett:
All of the function generators I've worked with in that price range (I've never seen anything more expensive because of educational budget constraints) have that problem. Spot-on frequency stability isn't necessary for most things, +/- 10 Hz isn't too bad. Just look at the FM radio bands, in the USA they skip every tenth of a MHz. You'll see 106.9, then 107.1 and so on. So when you consider that even these super high powered and highly regulated devices can't keep within 50 kHz of their band a +/- 10 Hz drift doesn't seem so bad. Really, it's necessary to drift that much because of the nature of FM radio, but I still think it's a good example. |
| septer012:
I don't think so ross.. I think they have that gap because the tuning filter in your radio is junk. There isnt a 16 pole filter in your clock radio. Edit: the spacing is mandatory by the FCC here in the states for better co-channel and receive-ability. |
| Andrew:
The specs say it has up to 1.5 % (in)stability at some frequencies. That would be +/- 30 Hz at your 2000 Hz. Your 1990 Hz to 2010 Hz are well within the specs. So you got what they promised. Not that I would have bought something with +/- 1.5 % stability, but they were at least honest upfront. If this happened right after you turned the instrument on then there is hope that it gets better. Instruments like these need to be "warmed up" before they reach their most stable operating conditions. This typically means to have the instrument running for at least an hour. I know instruments where the manufacturer even requires four hours warm up to reach the guaranteed specs. Some people therefore never even turn of instruments. However, the whole instrument as such looks like typical last decade Chinese design, copied from some western design from the '70 or '80 of the last millenium, re-badged for Madell. The OEM is likely Yang Zhong Ketai Electronic Instrument Co.,Ltd, alias Yang Zhong City Light and Electronic Instrument Factory, alias Micaltek, alias Caltek, alias Y-Caltek. As you see from the many names, we are deep down in the Chinese OEM naming game. And, of course, they have "tek" in some of their names in the hope that some of the reputation of Tektronix would rube off. This is your generator in its natural habitat: http://www.y-caltek.com/cn/products/generator.htm It is an outdated design, although designs like this are still sold by many, usual Chinese, manufacturers. Typically the stuff is robust but not very accurate. $250 is IMHO OK for such a generator, but not a bargain. BTW: If you want to learn, then one of the things to learn is that it is Hz and kHz, not hz and khz. Sloppy notation will bring you into trouble sooner or later. |
| qno:
Maybe your sweep input is picking up some hum or noise. Try to short circuit the sweep with a 50 ohm terminator or a short piece of wire. Is there an FM modulation input? If you short that maybe the stability improves. |
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