what should I look for when buying function generator? - EEVblog

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nour

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what should I look for when buying function generator?

« on: December 20, , 11:26:26 am » Hi, I would like to own function generator for the hobby and I don't know anything about what should I look for in function generators when buying them

I see gen. begin from around 50-60$ on ebay up to s $

I need to know what should I look for when buying function generator?

thanks

EDIT

By the way, for now I will not set a price limit, I just want to know what is the things that I should care about and the things that I should avoid « Last Edit: December 20, , 12:14:46 pm by nour » if what I have wrote doesn't make sense for you or you think there is something wrong, please correct me, I am still beginner and what I know probably less than what you know The following users thanked this post: Doogs

tautech

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Re: what should I look for when buying function generator?

« Reply #1 on: December 20, , 11:54:01 am » If you want a well featured unit this might interest you:
http://www.siglentamerica.com/pdxx.aspx?id=&T=2&tid=16

I might add if you buy the 40 MHz unit you might be able to improve it. 
https://www.eevblog.com/forum/testgear/the-siglent-sdgx-thread/msg/#msg

Avid Rabid Hobbyist.

PA0PBZ

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Re: what should I look for when buying function generator?

« Reply #2 on: December 20, , 12:43:20 pm » Excuse me saying this but if you have no idea what to look for, do you really need one?
If you do need one you must have an idea what you want to use it for and then you have a starting point: "Can it do what I want to use it for?"
Tell us why you want one and then maybe we could give you some advice.

Keyboard error: Press F1 to continue.

jpb

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Re: what should I look for when buying function generator?

« Reply #3 on: December 20, , 01:03:01 pm » The approach I took was to decide what sort of frequency range I might want to go up to in my electronics and then I kitted my lab out (gradually) with appropriate kit.

So I decided I wouldn't be doing GHz rf stuff but might want to run things up to around 50MHz at most. To look at 50MHz square waves (say clocks) needs a scope that can show 3rd harmonic and perhaps 5th harmonic without too much attenuation so I (a bit extravagantly) went for a 350MHz scope but my signal generator is the Agillent  one that goes to 30MHz including square waves.

Apart from bandwidth you need to decide whether or not you're bothered by jitter, whether you want low phase noise at audio frequencies, if you will want more than one channel and whether you might want to play back long arbitrary waveforms or perhaps have short pulses spaced by large intervals (which can be problematic for some signal generators). Do you want to have modulation and different wave shapes (square, triangular, arbitrary as well as sine)?

It is worth reading up about how these things work - an article I found most helpful was :

http://www.edn.com/design/test-and-measurement//09-01-98-Choosing-a-waveform-generator-The-devil-is-in-the-details

I don't know if the link is working but Google the title. There are also many guides from Agilent/Keysight and B&K Precision on line.

nctnico

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Re: what should I look for when buying function generator?

« Reply #4 on: December 20, , 01:26:54 pm » IMHO you can't go wrong with the Feeltech FYS as a first function generator. Even if you decide to buy a more fancy generator later on it will stay handy to have around. There are small lies, big lies and then there is what is on the screen of your oscilloscope.

nour

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Re: what should I look for when buying function generator?

« Reply #5 on: December 20, , 03:16:09 pm »

Excuse me saying this but if you have no idea what to look for, do you really need one?
If you do need one you must have an idea what you want to use it for and then you have a starting point: "Can it do what I want to use it for?"
Tell us why you want one and then maybe we could give you some advice.

I am creating my own lab and I am buying the basic insterments

for the fun. gen, I used one before 15 years ago  and it was very simple some knobs and buttons I remember it was 1 megahertz so I know what was function generator used to be 

for know I need to know more about modern function generator what do they provide so I can decide
For know I am intersted in digital electronics, power circuits and building test equipments
I don't want a brand name, I want some basic guidelines for deciding my self, after that I will as you guys to recommend one for me

thanks if what I have wrote doesn't make sense for you or you think there is something wrong, please correct me, I am still beginner and what I know probably less than what you know

nour

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Re: what should I look for when buying function generator?

« Reply #6 on: December 20, , 03:19:19 pm »

The approach I took was to decide what sort of frequency range I might want to go up to in my electronics and then I kitted my lab out (gradually) with appropriate kit.

So I decided I wouldn't be doing GHz rf stuff but might want to run things up to around 50MHz at most. To look at 50MHz square waves (say clocks) needs a scope that can show 3rd harmonic and perhaps 5th harmonic without too much attenuation so I (a bit extravagantly) went for a 350MHz scope but my signal generator is the Agillent  one that goes to 30MHz including square waves.

Apart from bandwidth you need to decide whether or not you're bothered by jitter, whether you want low phase noise at audio frequencies, if you will want more than one channel and whether you might want to play back long arbitrary waveforms or perhaps have short pulses spaced by large intervals (which can be problematic for some signal generators). Do you want to have modulation and different wave shapes (square, triangular, arbitrary as well as sine)?

It is worth reading up about how these things work - an article I found most helpful was :

http://www.edn.com/design/test-and-measurement//09-01-98-Choosing-a-waveform-generator-The-devil-is-in-the-details

I don't know if the link is working but Google the title. There are also many guides from Agilent/Keysight and B&K Precision on line.

that was very helpful
thanks a lot if what I have wrote doesn't make sense for you or you think there is something wrong, please correct me, I am still beginner and what I know probably less than what you know

Tom45

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Re: what should I look for when buying function generator?

« Reply #7 on: December 20, , 04:10:46 pm » The frequency range is important, both maximum and minimum frequency.

Also think about whether you might need two output channels or just one. And what maximum output voltage would you want.

I was about to buy a Rigol function generator until I realized that its 10 volt maximum output was only for channel 1. Maximum for channel 2 was only 3 volts. So I got the Rigol DG instead because I needed 2 channels with 10 volt maximum.

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Re: what should I look for when buying function generator?

« Reply #8 on: December 20, , 04:51:42 pm » Well, I can say nothing bad about my TEK AWG.

For me, the reason why I like it so much is that it has a very cool user interface. I do a lot of work with superimposed sine waves...and being able to generate one with the GUI (aka without the PC) is worth a lot to me.

Re price; I lucked out and got mine for 200 bucks. The case cant be opened due to dents and the NVRAM is fucked, but I stuck in a floppy for waveform storage between sessions and am a happy camper for now.

Re the Chinese: never had one. But I never bought Chinese for large instruments...and while most of my AliExpress orders worked for some time (eventually, every supplier starts to fuck up)...I would not buy a SigLent. Hell, I am even paranoid about Rigol even though their (sometimes VERY asinine) distro lives next door and is fluent in German and English. Feel like some additional tamile wisdom? Visit my YouTube channel -> https://www.youtube.com/user/MrTamhan for 10min tid-bits!

Smith

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Re: what should I look for when buying function generator?

« Reply #9 on: December 20, , 07:01:40 pm » I like trigger outputs (for scope triggering), and 10MHz reference in/outputs for devices with less stable clocks.  Also trigger inputs can come in handy, so you can start a slow ramp/triangle at an digital input for example.

What I like for testing filters and amps is a frequency sweep. I have 2 FG's with sweep options, and I use them quite frequently.

Its your call if you want/need RS232/USB/LAN/GPIB etc. It can come in handy for automated measurements.


Trying is the first step towards failure

Fungus

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Re: what should I look for when buying function generator?

« Reply #10 on: December 20, , 08:03:41 pm » a) Write down what you need from a function generator, and why you want one.

b) Find one that matches that specification, at a price you're happy with.

That's it.

If you're not sure about (a) then better not buy one yet. Get a $10 AD module on eBay and play with that.

http://www.ebay.com/sch/i.html?_nkw=ad

You need an Arduino or similar to control it, there's dozens of downloadable programs on the 'net.

nour

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Re: what should I look for when buying function generator?

« Reply #11 on: December 20, , 10:35:53 pm »

a) Write down what you need from a function generator, and why you want one.

b) Find one that matches that specification, at a price you're happy with.

That's it.

If you're not sure about (a) then better not buy one yet. Get a $10 AD module on eBay and play with that.

http://www.ebay.com/sch/i.html?_nkw=ad

You need an Arduino or similar to control it, there's dozens of downloadable programs on the 'net.

very helpful thanks, but I don't think I am willing to buy the module that you have mentioned
I want a real one not something to play with, and I have mentioned the fields that I am intersted in

no specific task to have function generator,  thats part of building my lab
and btw I don't think I will spend much on it, just something decent for now

thanks if what I have wrote doesn't make sense for you or you think there is something wrong, please correct me, I am still beginner and what I know probably less than what you know

nour

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Re: what should I look for when buying function generator?

« Reply #12 on: December 20, , 11:04:36 pm » After searching about the topic on google (thanks to jpb) I have found this article
http://www.bkprecision.com/support/downloads/function-and-arbitrary-waveform-generator-guidebook.html

very very good article about exactly what I was looking for
I encourage everyone to give it a try, it is very helpful for people like me who have a basic understanding of function generator insterment

I think after reading this article I will have a very good understanding and will help me to decide what I am looking for, at least will clear some fog 

one thing though it didn't tell me about is what should I avoid when choosing function generator
what makes a function generator distinguished from another one, I am not talking about the max frequency range or the features, but I am sure there is other factor, may be the noise or other stuff that I am not aware of if what I have wrote doesn't make sense for you or you think there is something wrong, please correct me, I am still beginner and what I know probably less than what you know

cs.dk

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Re: what should I look for when buying function generator?

« Reply #13 on: December 21, , 08:11:51 am » I'm a newbee too, but i thought i would chime in.

I've been building my self a little "hobby-lab", just to learn electronics and repair simple stuff. One thing that i have noticed is, multimeters and powersupplys, you can't have enough of them. (with some decent probes/test leads). I've got some good handtools, a decent soldering iron, and a DSZ.. A function gen would be one of the last thing i'm gonna buy, unless some specific task forces me to do so.

IMO there is a lot of other stuff, that are worth spending money on, to get started. Buy a FG when you actually have a need for it.

Just my 2c

TAMHAN

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Re: what should I look for when buying function generator?

« Reply #14 on: December 21, , 09:22:11 am » About my TEK AWG (which I really like). I bought it cause: a) cheap and b) had excess loot to burn for tax reasons.

I have built MULTIPLE DDS/AWG units with an MCU, some Opamps and shit. Doing so is a very interesting learning exercise...and if a) and b) werent met, i would probably still do so Feel like some additional tamile wisdom? Visit my YouTube channel -> https://www.youtube.com/user/MrTamhan for 10min tid-bits!

Smith

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Re: what should I look for when buying function generator?

« Reply #15 on: December 21, , 12:47:10 pm »

IMO there is a lot of other stuff, that are worth spending money on, to get started. Buy a FG when you actually have a need for it.

Indeed, I managed to do 10 years without any  FG. Yes it's handy, but I've always managed by building some circuit to fulfill the  (temporary) need.

Only reason to go get one immediately is for audio purposes. It's so easy to check amps, filters and such. Trying is the first step towards failure

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Re: what should I look for when buying function generator?

« Reply #16 on: December 21, , 08:04:05 pm »

one thing though it didn't tell me about is what should I avoid when choosing function generator
what makes a function generator distinguished from another one, I am not talking about the max frequency range or the features, but I am sure there is other factor, may be the noise or other stuff that I am not aware of

Most modern function generators (at least the ones that do different wave shapes) are DDS. These are good for sin waves given the right filters. They are good for square waves where the frequency  fits in with the memory and the natural cycle of the instrument - where it doesn't you can get a lot of jitter. Keysight/Agilent have a good (but expensive) approach to sorting this. Siglent have what looks like an effective solution for pulses. The thing to look out for is can they have a fast rising edge with slow pulses? If you have a short pulse stream but with a long gap between them can it get uniform pulse widths?

Another area DDS generators (as apposed to the old analogue ones) is in triangular waves. You will notice that the frequency specs for these is much lower than for sin or square waves - you need a lot of harmonics to get a good sawtooth.

The third thing to look out for is amplitude vs frequency. In the old days generators went up to a given amplitude (say 10V p-p) for a given bandwidth. But Rigol (I think it was) introduced increased bandwidth but at lower amplitude. The output amplifier has a gain-bandwidth product so by switching in a lower gain you can go to a higher bandwidth. In some ways it is a bit of a cheat but even Keysight/Agilent are following suit otherwise they can't compete on spec sheets. It is not entirely a con - it is useful to be allowed higher frequencies as long as you're aware  that you perhaps can only go to 1Vp-p.

The cheaper generators also tend to have more phase noise or harmonics though I think having an external clock reference can help. If you look on the Siglent thread (I forget the model number) on this forum you'll see some measurements taken on a spectrum analyser which are compared to (much better) output of an old bit of HP kit.

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Re: what should I look for when buying function generator?

« Reply #17 on: December 29, , 01:42:19 pm » I started with those small pcb based ones from ebay where you have a display and can adjust the signal type, amplitude, etc.  They also have a TTL type square wave output.  While they would get me out of a bind like bricking an AVR by changing the fuses to use a clock when there wasn't one, it falls so short to a decent AWG.

I bought a SDGX a few months ago and it is so much more capable.  Knowing what I know now, there is no way I'd spend $100 on a small board or cheaper AWG when for $469 after discount you can get a SDGX that can easily go to 120 MHz sine by simply using an arbitrary wave file.  The value and capability are so much higher.

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Re: what should I look for when buying function generator?

« Reply #18 on: January 01, , 06:48:59 am » I picked up this unit off Ebay as a starting point.  Been using it to tune the IF and basic 3MHz and less for AM radio repairs.  UDBS Function Signal Generator Source Frequency Counter DDS Module Wave 5MHz - http://www.ebay.com/itm/UDBS-Function-Signal-Generator-Source-Frequency-Counter-DDS-Module-Wave-5MHz-/?  for $34.00 you cannot beat that! 

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Re: what should I look for when buying function generator?

« Reply #19 on: January 01, , 08:28:36 am » I have two units pm Philips and, in my opinion, they have everything anyone could want from a function generator.
http://www.surplus-electronics.co.uk/index.php/en/Products//
Detailed characteristics are described in the manual you can download here:
http://elektrotanya.com/philips_pm_sm.pdf/download.html
This can serve as basic criteria for a good function generator.

billfernandez

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Re: what should I look for when buying function generator?

« Reply #20 on: January 01, , 05:35:32 pm » Nour: 
For your purposes you will at least have to make some guesses about what range of projects you think you might engage in.  In that light, you should look at:

o cost:  Buy something cheap just to get started, or buy something more expensive that you think might give you more long-term flexibility?
o frequency range:  Audio (say 40kHz), Bluetooth (2.4GHz), wireless remote control (412 or 900 MHz)?
o frequency accuracy.
o waveform fidelity, noise, distortion.
o jitter.  timing accuracy.
o voltage and current drive capability.
o waveforms:  Function generators started out being sine, triangle and square wave because they were easy to generate with analog technology.  Sine and square continue to be commonly needed.  But these days there's also often the need for pulse trains, digitally-encoded signals, modulated waveforms (AM, FM, PWM, etc.) and for "complex" waveforms such as would be found in EEGs, seismic sensors, etc.  In all these latter cases having arbitrary waveform generation capability is convenient.
o Might you ever want to control the generator by computer?  To download complex waveforms or digital pulse streams?  To coordinate a test setup with other equipment under computer control?  In these cases it's useful to be able to connect via Ethernet, and use SCPI commands to control the unit.
o User interface.  I find it a lot easier to punch buttons and get exactly what I want (digital, computer controlled generator) then to carefully twist knobs and read frequency and voltmeters to get what I want (analog controlled generator).

For what It's worth, I recently bought a Siglent SDGX because I wanted a general purpose function generator that would very versatile, be of good quality, have good performance, could be used for a wide variety of things, be easy to use, and that I could afford.  I think this was a good choice for me, but then I could afford $500 for a general-purpose signal source, and I don't do any RF work where I'd need much higher frequencies.







« Last Edit: January 01, , 06:07:43 pm by billfernandez »