Re: [Phys-L] Function / Signal generators for undergrad labs

[John Denker <jsd@av8n.com>]

On 9/8/23 2:38 PM, MacIsaac, Daniel via Phys-l wrote:
> we are looking to replace a dozen Function/Signal generators

Please allow my to interpret "replace" in an extra-broad sense.

YMMV, but speaking for myself, my experiments typically have a
computer or two attached. Since the early 70s people have been
saying I have a Midas touch: Everything I get my hands on turns
to software.

In particular, typically when I want a function generator the
function is a lot more complicated than anything a "function
generator" can produce. For example, consider a spread-spectrum
sonar pulse. Start with a delta function, then scramble the phases
so that it looks more like white noise. This lowers the instantaneous
peak amplitude by approximately a factor of infinity. Unscramble
the return signal to achieve 100% of the resolution you could
have gotten from a delta function in the same bandwidth. Note:
Not an original idea. Whales have been doing it this way for tens
of millions of years.

So ... assuming there is (or could be) a computer nearby,
rather than shopping for a "signal generator" consider
shopping for a usb DAC power amplifier. There's a mass market for
such things, so you benefit from economy of scale. It is easy to
find ones that go up to 384 kHz (which is less than the 4 MHz
rating of the B&K 4001A but still good enough for many purposes).
Also it will go down to millihertz or microhertz frequencies
including DC (which the B&K 4001A won't). Rated for hundreds of
watts. Low 8 ohm output impedance (compared to 50 ohm for the B&K
4001A). Not sure how well they do with shorted outputs, but likely
OK, likely enough that it makes sense to buy one and do the experiment.

In terms of complexity, this raises the floor and greatly raises the
ceiling. That is: experiments that would have been ultra-simple become
slightly more complex, while fancier experiments that would have been
difficult or impossible become doable with only modest effort.