On Sun, 18 Mar 2012, Antonio I0JX wrote:

The frequency stability of my HP3312A function generator is poor, very
annoying for any practical use. I am trying to determine whether that
behavior is fairly normal for function generators, or my particular unit has
got a problem.

A function generator, by definition, is a generator that can put out
multiple waveforms. They are also generally audio and low RF (ie hundreds
of KHz) generators. They are great as a signal source when you need a
triangle or square wave, not so great if you need a sinewave. And despite
them running at "high frequencies" that doesn't mean they are the best
choice for that.

I see it all the time (or used to) in sci.electronics. basics People
would ask about why their 2206 or whatever function generator IC wasn't
very good at the top of the range (whatever that was, 1 or 2MHz). The
answer was obvious, it was the top of the range, pushing the limits of the
device.

But they had no experience with RF, so they thought they could extend the
nominally audio device to low radio frequencies.

Switch to something that is made for RF, and you immediately get better
results, without any real effort. It's easy to build an LC oscillator at
1 or 2MHz, "way down there", but to stretch an RC oscillator to 1 or 2MHz,
"way up there" is pushing things.

Get an RF mixer, and some crystal oscillators, and use that to mix the
audio or low RF frequencies up to where you need them. Not perfect unless
you can get rid of the image, but the function oscillator stays where it
is stable, and you can use it as the variable element of the "oscillator",
complete with sweep function (if the function generator has a sweep
function) and multiple waveforms.

Michael VE2BVW


What is your experience on function generators frequency
stability?
Thanks & 73

Tony I0JX
Rome, Italy