Pointy Sine Wave from BK 4017A Function Gen. - Page 1
Forum section: electronics / testgear

author: opensourcefan
author_rank: Contributor
timestamp: February 06, 2016, 11:05:36 pm
content: I have a very pointy Sine Wave being generated from my BK 4017A F-Gen. From my previous reading I believe it uses a diode clipper circuit to clip the Triangle Wave into a Sine Wave...Is there anything I can adjust or do to smooth the pointyness of this wave? Is this an issue when I'm experimenting in ciruits with this wave? My XR2206 created a much more pleasing to the eye wave than this.Previous reading -https://www.eevblog.com/forum/testgear/waveform-generating-displaying-question/msg581655/#msg581655

author: Performa01
author_rank: Super Contributor
timestamp: February 07, 2016, 09:30:35 pm
content: Do you have a service manual, or at least the schematics?These function generators usually have an alignment for lowest sine wave distortion, which will influence the wave shape obviously. The correct method of alignment is trimming for minimum reading on a distortion meter – and that might not lead to the most pleasing (to the eye) wave shape.It is quite funny, that even distortion levels <1% may still be visible on a scope. The ‘pointiness’ might look ugly, but does not necessarily produce very strong harmonics, hence your generator might still be within spec, which would generally be no better than 0.5% at best, I would suppose.

author: opensourcefan
author_rank: Contributor
timestamp: February 08, 2016, 02:06:38 am
content: Sadly I don't have a service manual or schematics, only the linked manual. The specs for it's Sine wave are:SINE WAVEDistortion 3% typical at 1kHzFlatness (into 50 ?) ±5% (.45 dB) 0.1Hz to 8MHz, ±20%(2.0 dB) 8MHz to 10MHzIf it's just a visual thing I can deal with it, if it's going to produce bad results I don't have the experience to know otherwise so I guess I can deal with that as wellWas just curious if there was a known setting for rounding it out but hard to know without the manuals I guess. I'll probably open it up at some point for fun, I'll take a look around and see what I can see. There doesn't seem to be a big user base of this unit so pictures and details seem to be limited.

author: Performa01
author_rank: Super Contributor
timestamp: February 08, 2016, 02:45:05 am
content: Sorry I've missed the link to the manual.But now that you provide the data I am quite surprised to see a specification of 3% at 1kHz. I honestly thought that none of the analog function generators I ever owned had more than 1% distortion and that would be pretty much standard for any such device.Well, at least for my last one it's easy to find data on the web, as it was a Hameg 8030-5, and this is indeed specified as <0.5% up to 100kHz.So it seems that the BK4017A is particularly poor in this regard and the 'pointy' sinewave is just its trademark. Despite all this, I still believe it will actually perform a bit better than 3%, but it certainly has not been optimized for low distortion.Anyway, don't worry about that. A traditional (analog) function generator like this has never been a suitable device for generating low distortion sinewaves anyway. It is still good enough for checking the frequency response of amplifiers and simple filter networks, whereas such a generator simply isn't meant for precision tasks, whether its distortion figure is 3%, 1% or even just 0.5%. Back in the days when analog generators were still popular, dedicated Wien-Bridge Oscillators have been used for generating low distortion (<0.01%) sinewaves, whereas nowadays most DDS function generators can provide at least distortion levels <0.1%, hence the need for specialiced low distortion sinewave generators has decreased significantly .

author: opensourcefan
author_rank: Contributor
timestamp: February 08, 2016, 02:52:52 am
content: Thanks for the info, feel better about it now. It was only $45 so not too worried, although I can't believe something like this lists for hundreds. Would much rather have a good DDS instead for that money.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 08, 2016, 11:24:42 am
content: Hmm... that looks pretty pointy all right. I think if it were mine I think I'd try to tweak it somehow. My old Interstate (Racal-Dana) F43 looks a little better than that.In the screenshot below, the yellow trace is the output from the F43, turned up pretty high to give 20 V p-p into a 50 ohm thru-terminator at the scope. The purple trace is from a cheap DDS FG (MingHo MHS-5200A) , connected directly (no terminator) to the scope, with its amplitude set at "1.94V".

author: opensourcefan
author_rank: Contributor
timestamp: February 08, 2016, 12:45:16 pm
content: Thanks for details. I'd love to tweak it just don't know how at the moment. Maybe I can find a service manual for a different Gen in the same line. Sure would be more visually appealing to smooth it out.

author: GAD
author_rank: Regular Contributor
timestamp: February 08, 2016, 05:30:35 pm
content: Quote from: opensourcefan on February 08, 2016, 02:52:52 amI bought one of these new a while back and returned it within an hour of receiving it. I think you paid the right price for it.I got an Agilent 33120A on eBay for the price of the 4017A new.

author: opensourcefan
author_rank: Contributor
timestamp: February 08, 2016, 05:44:36 pm
content: Ya, after watching a bunch of YT videos on the cheap overseas ones I can't say that this is much different. I'm happy with the price as it's interface is nice to use. I'm also a super beginner so can't justify a real good one yet either.