what is the difference between a signal gen and a function gen - Page 1
Forum section: electronics / beginners

author: nrgeek
author_rank: Contributor
timestamp: January 29, 2012, 03:51:33 pm
content: Im trying to decipher, between these are they really different and how they differ... Ive seen alot of folks on the net call a signal generator a function generator and vice versa .. like on you tube .. they will be talking about a signal generator and the machine clearly says its a function generator.Then the second part is .. what to buy ?I know the question is coming what do you want to use it for lol .. well me personally I have a old analog scope tek 475m, I'm mainly looking for tools to help diagnose issues on system boards etc for electronic repairs.. and in building small projects from scratch.And don't say I will know I need it when I need it lol .. I hate that . I wana have it before hand .. so when I know I need it I will already have it loland the next factor is cost .. I'm a newbie as you can tell .. and cost is a major factor .. I want functional yet low cost .. at to me that is 75 USD or less !Signal GenIve seen a ton of old ones on ebay and some little kit ones boards only no box.Is the old analog signal gens like heathkit , BK, and others .. , then there are some in the same section called signal gen that are ntsc obviously some type of tv / video signal gen.Function gen-Sweep function models, elenco 1mhz function gen kit, and on and on and a wide variety of hzI hope I get good responses to this .. as it will help many in my same boatThanx in advanceSean

author: olsenn
author_rank: Frequent Contributor
timestamp: January 29, 2012, 04:12:56 pm
content: Signal Generator, Function Generator, and Waveform Generator are all sometimes used interchangably; what you are looking for is a general purpose (not NTSC video generator) generator that will produce sine/square/triangle/ramp waves, and possibly pulse and/or noise waves, all at selectable frequency and amplitude (and duty cycle where applicable). Sometimes more expensive generators will also do things like AM/FM/PSK modulation, sweep, and include other useful features like a frequency counter.Something else you will need to watch out for is whether it is digital (DDS) or analog. DDS generators offer greater control over frequency and provide a more stable output over time (analog ones drift over the years). Also, some generators will allow you to create any arbitrary signal on your computer and transfer it over to be output; this is useful if you use LabView and want a non-standard waveform.If you just want a basic DDS generator that will do sine/square/ramp waves at a selectable frequency/amplitude/duty, then I suggest the SFG-1003 (http://www.testequipmentdepot.com/instek/signalgenerators/sfg-1003.htm). It is cheap, reliable, and suitable for most work with no thriills.If you want a more fully featured DDS arbitrary waveform generator, than I recommend the Rigol DG4062 (http://www.tequipment.net/RigolDG4062.html). It is the best device you will find at that price range and does all the above mentioned advanced functions.

author: nrgeek
author_rank: Contributor
timestamp: January 29, 2012, 07:03:17 pm
content: both of those are way out of my price range, I only paid 85 for my old Tektronix 465m, I know you gotta pay to play .. but I need to pay much less lolIm just getting into all this and not wanting to spend more than I have to .. I have to keep the cost under 75 us dollars .. I will upgrade later when I can afford to .. what This model I found in my price range GW Instek GFG-8020H 2MZhttp://www.testequipmentdepot.com/instek/signalgenerators/gfg-8020g.htm

author: nrgeek
author_rank: Contributor
timestamp: January 29, 2012, 07:11:29 pm
content: Of course I found one used not the price they have it for of almost 200 bucks ! .. I found one under 100

author: Unknown
author_rank: Unknown
timestamp: January 29, 2012, 07:31:29 pm
content: Note that this is an old-style analog function gen that generates a triangular wave and runs it through sine shaper that makes it into something that looks kind of sinusoidal on a scope. Hence the 1% distortion spec in the audio range, and even worse at higher frequencies. They didn't even bother to spec it above 200 kHz. Not critical at all for many applications, but something modern DDS generators are much better at. Same for frequency stability, since these usually use a simple RC oscillator, while DDS generators use a crystal oscillator as frequency reference.In my opinion $100 is fairly expensive for a used entry level 2 MHz function generator. I see several Wavetek and HP function generators on eBay for similar or lower prices, with better specs and better quality. I haven't done the research into their condition, but in my opinion you should be able to do better on the used market. Note that this is for analog function gens (which have served many people just fine for many years), used DDS gens are much less common because the technique trickled down into the entry level function gens relatively recently.

author: ejeffrey
author_rank: Super Contributor
timestamp: January 29, 2012, 07:58:12 pm
content: Function generators tend to be signal generators that focus on low frequency, but with very flexible waveforms. Your minimum for a function generator would be sine, square, and triangle, with most offering adjustable duty cycle / symmetry for the square and triangle waves, as well as pulse generators. Fancier models provide triggered pulse bursts, sweeps, and AM/FM modulation. The logical conclusion of the function generator is the modern DDS, which is basically a DAC, and can output any waveform you choose within the bandwidth and memory limits of the device.Signal generator is a more generic term, but would frequently refer to RF or audio frequency sine wave generators that are designed to generate signals with very high spectral purity and stable frequency and amplitude. On the other hand, DDS function generators are generally stable but still have quite a bit of jitter, while analog function generators drift all over the place.

author: nrgeek
author_rank: Contributor
timestamp: January 29, 2012, 07:59:14 pm
content: I found that one on ebay for $45 shipped .. I guess I will try it out .. if it does not do the job will look fr a higher end model later, it was cheaper than any others I could find, since Im just learning how to use all this stuff .. I would rather not break the bank to learnResponses have been very helpful thoughThank You

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 29, 2012, 08:00:39 pm
content: Hantek DDS3x25has becoming more and more usefull for me. limitless from sub hertz to audio to 100MHz, arbitrary anything wave you can imagine etc. the only drawback is it uses PC to control/change the signal... and uncertain noise/jitter level which critical to low noise system incl audio, but the later... not even Dave can afford the low noise signal generatorjust add few bucks and get this "beyond limit" AWG/FG. my 2cnts.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 29, 2012, 11:05:25 pm
content: A Signal Generator is a serious piece of test equipment which is usually found in Electronics Workshops.A Function Generator is a toy found in Engineer's home labsBut seriously,the above is fairly close to correct.Normally a Signal Generator is used to test made up equipment,where calibration accuracy & wide frequency range of the signal source is important.Function Generators are more often used as a convenient signal source for circuit modules in the initial testing stage,& are usually not as elaborate,or highly spec'd as a Signal Generator.That said,there are some pretty basic Signal Generators,& some pretty fancy Function Generators,so like many things in Electronics,the boundaries become a bit blurred.The NTSC or PAL things generate analog TV signals,& unless you are playing with analog video are not a lot of use.Many of them are Tektronix,though,& will be full of high quality parts if you can get them cheaply.VK6ZGO

author: nrgeek
author_rank: Contributor
timestamp: January 29, 2012, 11:49:15 pm
content: SO vk6zgo .. how about some recommended signal gens brands, and prefer links as well , for us folks that dont have a clue but want one lolUsed 50-150 , 150-200, 200 -500 analog and digital please

author: tinhead
author_rank: Super Contributor
timestamp: January 30, 2012, 12:18:48 am
content: Quote from: nrgeek on January 29, 2012, 11:49:15 pmRohde & Schwarz, price (used) from 500$ (e.g. SMX ) to "you can't pay", but let stay realistic SME 0x for 3-5k $

author: Rufus
author_rank: Super Contributor
timestamp: January 30, 2012, 12:20:26 am
content: Quote from: vk6zgo on January 29, 2012, 11:05:25 pmAnything that generates a waveform can be described as a signal generator. Function generator describes something that generates particular waveform(s). It probably goes back to the days of analog computers the shape of the waveform being described by a mathematical function.

author: Unknown
author_rank: Unknown
timestamp: January 30, 2012, 12:21:25 am
content: HP/Agilent made and make some nice RF signal gens (and tons of other signal generators). R&S and Marconi were/are two other brands. A signal generator is a more specialized bit of kit. For example, an RF signal generator can usually only generate sinusoidal signals, has less low frequency range, and a more limited output amplitude. They tend to have a much higher max. frequency, a much more stable frequency, and various types of modulation. The HP 8640A/B is quite popular, though it can suffer from cracked gears. Expect to pay closer to the $500 than the $50 mark. For cheaper signal gens, you'd have to go farther back in time, like the HP 608. Seeherefor a history of HP sig gens.A signal generator is a fairly specialized piece of kit, a function generator is much more versatile (jack of all trades, master of none). I would get a function generator before getting a signal generator, and would question the value of a signal generator for someone not doing RF.Quote from: Rufus on January 30, 2012, 12:20:26 amThe term signal generator is not typically used for function generators or pulse generators, however. Signal source is the generic term. HP made an instrument that was not as stable as the real signal generators, so they called it something like 'RF signal source'.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 30, 2012, 04:38:59 am
content: Quote from: nrgeek on January 29, 2012, 11:49:15 pmThe Major Electronics manufacturers used to make their Sig gens in house up to the 1950s,but most of them gave up,& the few specialist companies took the market.In reasonably "modern" types,you may find:- HP/Agilent,Marconi,Philips,Rohde & Schwartz, Metrix,Racal,IFR,etc.Some of the old "tube" type stuff is very good,but is getting pretty "long in the tooth" these days,so I wouldn't advise getting them.There are a lot of good solid state units from the '70s,'80s & '90s around.I'm pretty much "out of the loop" these days,so can only suggest,EBay,Hamfests,local newspapers,etc.Some Universities & Tech Colleges had pretty good gear that they may be getting rid of,so that's another possible avenue.VK6ZGO

author: Rufus
author_rank: Super Contributor
timestamp: January 30, 2012, 05:32:53 am
content: Quote from: alm on January 30, 2012, 12:21:25 am"The World's Fastest and Most Versatile Signal Generators for Today's Complex Signals." Is how Tek describe their arb/function/pulse generator range. BK Precision list all their generators under that generic term. Agilent separate them but feel the need to annotate "Signal Generator" with (Signal Source) for their audio, rf, and microwave generators.The source of all knowledge says "Signal generators, also known variously as function generators, RF and microwave signal generators, pitch generators, arbitrary waveform generators....."I would say Signal Generator is the generic term.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 30, 2012, 10:29:22 am
content: Wikipedia is not the ultimate reference source in the Universe!OK,the term "signal generator" can be used for any device which produces a signal,& in fact could even be used for a microphone,or a simple 555 oscillator,but common usage has tended to be that which I suggested earlier.Tektronix's sales department has seen better days,so are quite happy to produce such a statement.I feel that their Engineering department will still make the distinction.VK6ZGO

author: gregariz
author_rank: Frequent Contributor
timestamp: January 30, 2012, 06:26:52 pm
content: Quote from: Rufus on January 30, 2012, 05:32:53 amTechnically thats correct but "sig-gen" in common usage means RF signal generator. Likewise if you asked for a "sweep-gen" you'd get an RF sweeper. If you want to test audio/low frequency stuff you'd ask for a function generator or audio oscillator.

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 30, 2012, 08:03:54 pm
content: Another naieve question, this time re arbitrary function generators, so i thought I would ask here? I work in automotive spheres, often wiring after market user mappable electronic engine control units. I am looking for a way of bench testing the ecu and loom by feeding it signals similar to those a live engine would do. If I have a crank trigger with 38 teeth, but with two missing, sensed by a magnetic or hall effect sensor outputting to an ecu input, could I feed these signals into an AFG and have it "log" this waveform and duplicate it away from the source (sensor) later? What sort of voltage amplitude will they, on average, output? Thanks.

author: Rufus
author_rank: Super Contributor
timestamp: January 30, 2012, 08:19:07 pm
content: Quote from: Chris Wilson on January 30, 2012, 08:03:54 pmNo, but, you could capture the signal with a digital scope and with a varying amount of difficulty depending on scope, arb and software for both load the arb with the captured signal. You can also 'draw' the signal yourself and load it into the arb - probably easier in cases like this. You can adjust the signal frequency and amplitude on the generator but remember real world signals like this are likely to change shape with frequency.Quote from: Chris Wilson on January 30, 2012, 08:03:54 pm50 ohm output impedance and +/- 10v into an open circuit is typical.

author: gregariz
author_rank: Frequent Contributor
timestamp: January 30, 2012, 08:41:13 pm
content: Quote from: Chris Wilson on January 30, 2012, 08:03:54 pmThis is kind of a trick for new players. Function/Arb generators have quite a variation in output impedances and voltage levels available. Some will have 600 ohm outputs and others will have 50 ohm outputs, some have TTL outputs. Some have all of the above. Others will have switchable output attenuators, kind of like a "sig-gen". Others again will simply have a variable pot to control output while others again have separate high and low outputs. High outputs may be as much as 20 volts or so. High impedance outputs are kind of nice if you are trying to drive some logic or test microphone circuits. The lower impedance are just as usable but you might want to often use some series resistance.

author: Unknown
author_rank: Unknown
timestamp: January 30, 2012, 11:46:52 pm
content: Quote from: Rufus on January 30, 2012, 08:19:07 pmExcept for the Hantek USB afg that's somewhat popular on this forum.Quote from: gregariz on January 30, 2012, 08:41:13 pmAre there any common arbitrary function generators that have an output impedance other than 50 ohm? I guess there may be some specialty 75 ohm onces for telco/video, but I don't expect many arbs with 600 ohm output impedance, what's the point of an arb for audio? A very pure sine and occasionally a square and triangle are usually all you need. The only TTL output I've seen on arbs are sync outputs.

author: vk6zgo
author_rank: Super Contributor
timestamp: January 31, 2012, 12:22:45 am
content: Quote from: Chris Wilson on January 30, 2012, 08:03:54 pmBack in the day,this would have been done with hardware.All you need is two pulse sources,locked to the same reference,with one running all the time at the "38 teeth " rate,& another which produces a blanking pulse every "36 teeth" to blank out the 2 teeth pulses you don't want.Actually,thinking about it,you really only need one pulse source & a few CMOS counters & gates.Still a bit complex,but not rocket science!VK6ZGO

author: gregariz
author_rank: Frequent Contributor
timestamp: January 31, 2012, 12:38:02 am
content: Quote from: alm on January 30, 2012, 11:46:52 pmI used to program bitstreams into an HP8904 that had those options. But you are probably right that the newer Arb's don't, although its not really my area so I don't know everything thats out there. We had a complex signal generation need about a year ago and we actually didnt go with a discrete instrument. We instead used a NI cardframe with the various plugable bits hooked into labview that lets us capture/modify and replay.

author: Unknown
author_rank: Unknown
timestamp: January 31, 2012, 12:46:30 am
content: I stand corrected, this instrument indeed appears to have a 600 ohm output option. Not exactly what we associate with the word arbitrary waveform generator these days, though.

author: gregariz
author_rank: Frequent Contributor
timestamp: January 31, 2012, 01:04:56 am
content: Quote from: alm on January 31, 2012, 12:46:30 amYes, it couldn't compete with the newer instruments. It should do what the poster wants in terms of playback, and it has gpib so technically you could capture the input with a DAQ card and playback using the 8904. I think an easier method would probably be just one of NI's DAQ modules, some of which are pretty cheap (~100?), and use labview to program the capture and playback. On the other hand the 8904 was a popular bit of kit and just checking ebay its also seems pretty cheap.

author: Rufus
author_rank: Super Contributor
timestamp: January 31, 2012, 01:08:17 am
content: Quote from: alm on January 30, 2012, 11:46:52 pmMost of the TTi range are 50/600 switchable.