The frequency generators I have top out at 1Mhz, and their square wave output at 1Mhz is HORRID. While working on switched mode power supplies and FET drivers, I have often had to put signal conditioners on them for cleanup. So I came up with a goal to make a new freq gen One that would top out at 10Mhz, be USB controllable but only have TTL output. (which is more times than not, all I need) As it turns out, trying to generate a base clock from 1Mhz to 10Mhz was REALLY difficult! I went thru quite a number of oscillator designs just trying to get that range. When I got there, I had two problems. The first problem was stability, at one point I determined that one of my circuits jumped up by about 40Hz due to the thermal change of me walking up to it! The second problem was the output signal at 10Mhz I was getting some HORRID ringing from the oscillators. In the end, I broke down and got an Si5351 board its brutally stable and the output is pretty clean. I use 7 /10 stages to get down to 0.1Hz. The output is driven with a 74HC244 with 7 parallel outputs. It has manual control on the front. I have not written in the USB control yet. I'm playing with a state machine to accept numbers, cause ya know, backspace. This project was a great adventure on building 'wide range' VCO circuits. Everything from RC oscillators to ring oscillators to high freq beat freq systems. I learned lots. Got a great freq generator out of the deal too!