Signal generators/DDS signal generators

[eccerr0r]

How many of you have a signal generator and do you use it often, and what for?

I'm debating whether I should build a small low frequency DDS sig gen, or perhaps even get a calibrated sig gen instead of using the Eico 320 and 324 that I have for radio experiments... They do work, but look at this carrier wave (from my Eico 324, AM internal audio oscillator modulation of its radio frequency oscillator):

This does work for radio (AM radios can clearly pick it up, and even FM radios depending on detector), alas amplitude is not stable nor is the shape of the wave, as can be seen...

The envelope of the RF is also supposed to be a sine wave and you can see that the up slope is slower than the down slope; good enough for testing but that's a very distorted sine wave...

About all I have now, if I need a oscillator, are my Eicos or a 555...

[japlytic]

Re: Signal generators/DDS signal generators

I have a signal generator (for RF with AM/FM modulation) and a function generator (for all other applications including digital logic clocking/gating).
For a variable AC power supply (normal 50/60Hz or 400Hz mains frequency) made from a modified high power car stereo amplifier, a low cost DDS sinewave generator I constructed from an eBay ATMEGA16 kit (note the ATMEGA16 is preprogrammed and code protected) fits the bill nicely.

[eccerr0r]

Re: Signal generators/DDS signal generators

Hmm... currently playing with a cheapo DDS software for an AT90s2313 (since I have a pile of them...) Doesn't get fast and doesn't have adjustable amplitude. Wondering if I should get a real DDS/function generator that has both, and something that is or can be calibrated...

Part of the issue is trying to get a scope calibrated... Alas, bad when you don't have a good standard. Right now I'm basing calibration on an out of calibration Fluke 77.

I have a pile of crystal oscillators for digital logic but of course I can't adjust them, other than swapping another one in... An arbitrary function generator would be nice

[stj]

Re: Signal generators/DDS signal generators

there is probably a project you can build based on STM32, that is the cpu of choice now.

[eccerr0r]

Re: Signal generators/DDS signal generators

There are some dedicated DDS chips out there like the AD9915 from Analog Devices that could do the same without writing custom code...

oh boy, did not realize that DDS has gotten this fast already...

[diif]

Re: Signal generators/DDS signal generators

I was looking at these yesterday. http://www.ebay.com/itm/DDS-V2-0-Fun...-/321820490275

[eccerr0r]

Re: Signal generators/DDS signal generators

We know any DDS that includes the "ECG" waveform is just a toy. At 1BPS^H^H^H^H^H 1 Hz, it was meant for roll mode DSOs to make sure they're alive...

I just overclocked my 10MHz AVR being used for DDS to 14.31818 MHz as it was the only sane crystal I have on hand... surprised, 43% overclock... and it still works...

[stj]

Re: Signal generators/DDS signal generators

why surprised?
unless it's an "L" part it will be rated at 16 or 20MHz

[eccerr0r]

Re: Signal generators/DDS signal generators

It's a older AT90S2313-10PI (NOT a Tiny2313).

[stj]

Re: Signal generators/DDS signal generators

i was expecting a MEGA series!

[danito]

Re: Signal generators/DDS signal generators

http://www.ebay.com/itm/25MHz-Dual-c...-/400976855749

[eccerr0r]

Re: Signal generators/DDS signal generators

I know this AT90S2313 "homemade" DDS I have is very jittery due to software design, I wonder how good the other AVR DDS's fare in terms of jitter.