a 20mhz generator would be a max038 and dds related boards
xr2206 goes up to 1mhz
You have already made cheap dds generators and boards on many websites, why taking the hard route
I wish Dave would do a blog on the futility of DIY and hobby interest in electronics these days with so much already available far cheaper than you could make it yourself. One of the big advantages of Electronics Magazine projects was that you could make some thing cheaper and maybe better than a commercial design. No wonder it is dying out if the number of such comments I have been reading here lately is a reliable guide.
The only thing that gives me pause to have doubts is that it is said only when someone suggests they want to do it for some unknown reason.
I picked up a couple of MAX038 a while back for A$3 and hatched another dream of some project which may, but probably won't, see the light of day. I was going to make Dave's function generator design. You can't get the output buffer chip he used and I have to source another and then see if I can figure out how to adapt the design and maybe learn Kicad so I can make a PCB. Then make the PCB and solder it up and probably debug it. Honestly, what an idiot, why would I bother? I've already got so many other projects I'm also not working on and probably shouldn't bother with either.
I also wish I hadn't bought some of the parts to make the EMC probes Dave built. Luckily I saw the comments that you could buy them so cheap before I wasted time on them.
Unfortunately I realised too late when Dave said any modern DSO should be OK he wasn't saying Dick Smith Oscilloscope
*. My 10MHz single channel one isn't the DSO he had in mind.
(*) - Yes I am well aware that no Dick Smith Oscilloscope was ever
modern.