Should I get a function generator?

[tggzzz]

It is no use buying a scope to make accurate frequency measurements unless there is also a separate frequency counter buried inside the same case - which won't, in general, be true.

Granted, it wasn't true of many old analog scopes.

But are you aware of a currently manufactured digital scope that doesn't have a frequency counter buried inside the same case?  I figured that if it's a standard feature of the bottom of Rigol's line, it's probably on most other maker's scopes, as well.  I just checked some users manuals, and the $290 Owon SDS5032E has it, as does the $280 Siglent SDS1022DL.  So does the $340 GW Instek GDS-1072A-U.  These are not high-end scopes.

I went back over the thread, and the only place I see someone claim that a scope is good for accurate frequency measurements, they've qualified that by saying a "modern" scope.

The last time I bought a 1GHz 40MS/s scope, it didn't. But then HP's philosophy was that the instrument should do one thing well, rather than gain "marketing festure" brownie points by doing two things less well.

[jamesd168]

Is that 1 part in 10^7 resolution, repeatability, accuracy? How does it achieve that, other than by having an internal frequency counter?

Not sure about exact specs, but many modern DSOs have an internal frequency counter with accuracy governed by the scope's internal clock.  The counter counts the scope's trigger signal.  I know the Rigol DS1052E has this feature.

wow, these things are really inexpensive.

[guygibbs]

I'm not sure if this helps well actually I'm sure it won't but I'm a newbie and I have recently built an arduino & 386n-1 triangle square sawtooth and sine generator and have yet to use it haha but high insight I got an android app that worked from the start and is very useful and I didn't have to troubleshoot anything although that is where the learning comes in most . So if you just want to get some signals on screen and learn scope go with the app. If you need more than 2v. Then build one or of course purchase as needed ! Just my 2cents

[Lightages]

I have been mulling over this need or want for a function generator. Some people have already made the statement that two mulitmeters would be a priority over a function generator. I would tend to agree The order of importance to me would be:

1: Two multimeters of good quality
2: Oscilloscope
3: Dual rail adjustable power supply
4: Function Generator

This is all according to what you are actually working on however. If you need a function generator then a second multimeter does you no good. The best is to have all four of the above as a minimum. Perhaps a sound card output can function for what you need, but only up to audio frequencies. For many people that is enough.

So the grey area wishy washy answer is "It depends".  If you need a binary answer, then "Yes you should get a function generator".

[timb]

Is that 1 part in 10^7 resolution, repeatability, accuracy? How does it achieve that, other than by having an internal frequency counter?

Not sure about exact specs, but many modern DSOs have an internal frequency counter with accuracy governed by the scope's internal clock.  The counter counts the scope's trigger signal.  I know the Rigol DS1052E has this feature.

Yup. It generally only applies to the trigger.

Here's an example; notice the trigger frequency (triggering off CH1) is 10.0001MHz while the CH1 measured frequency is only 10.00MHz.

Ignoring for a moment my important caveat "other than by having an internal frequency counter", I'm afraid that, on its own, that's not convincing. But then I'm picky because I know of at least one (very expensive) attenuation test set that had a resolution and repeatability of 0.001dB, but the accuracy was only 0.1dB, i.e. 100 times worse. The accuracy wasn't important since the customer was interested in changes in attenuation (over time and temperature), not the absolute attenuation.

I could dream up several scenarios, e.g. the measurement being quantised in 1MHz steps and with the 0.0001 being a result of sloppy arithmetic! Now I strongly doubt it is that extreme, but if there isn't an internal frequency counter I'd like to know how it is done.

Does the manual have any specification for the frequency display's operation, resolution and accuracy?

The trigger circuit is generally a lot more sensitive and higher resolution than the actual inputs of any given scope. Take for example my Tek MSO2024B; the trigger goes up to 500MHz whereas the scope's bandwidth is only 200MHz.

When you think about it, a trigger circuit is just a frequency counter without the counter. On a DSO it's dead easy to count the trigger pulses digitally. Thus you get a high resolution frequency indication free of charge.

It's not some bloaty added feature. It's just how the scope works.


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[alterbaron]

Is a function generator of equal "must have" value or is it a "have one; rarely use it" kind of think for you?

Depends on what you want to build / test / learn about.

For tinkering with analog circuits (amplifiers, filters, .etc) a function generator is an indispensable tool.
If you're working mostly with microcontrollers and digital logic, it may be less useful.

Basically, having a function generator saves you the trouble of having to build an oscillator every time you wish to inject a signal into your circuit.
If the price of the function gen is lower than the hassle of rolling your own oscillator every time you need one, then pick one up.

[Amra]

You could always make one as a project, maybe use the XR2206 chip.  The chip only costs around 8USD, and there are plenty of open source circuits floating around for making a pretty good generator with it.  Depending on what you have in your parts bin, the whole thing could cost you next to nothing.

They are quite useful, depending on what you do.  Signal injection/tracing is quite useful for diagnosing circuits that aren't working, you can also use them to find out what kind of transformers you have in your parts bin or salvaged ones (i.e. their turns ratio), you can use them to for comparing audible signals, or as a temporary oscillator/timer while prototyping, you can even use them to test things like LC filters.  I'm sure there are a lot more uses, those are just the ones that came to mind.