On 01/04/16 19:23, very_fuzzy_logic@... [TekScopes] wrote:
I too have a variant of the NC7SZ14 fast edge generator. Mine follows a 28MHz DIP crystal oscillator so the rep rate is fast enough to use with a7T11. It is air wired with SMD components directly on a SMA socket, there is a 220R / 50R divider to minimise the current requirement (200mV into 50 Ohm terminated both ends) I see 500psec rise and 200 psec fall with an S4 sampler. There is a few percent overshoot and I plan to build another with a better ground plane.
Interesting.
My new variant will have a external input and a internal RC schmitt trigger relaxation oscillator. The external inputs will be unterminated, 50ohm to ground, 120/82 ohms to Vcc/Gnd for 50 ohms to the threshold voltage. The input will also be AC or DC coupled. There will be some reflections etc, but that won't be a major problem since the external input will drive a schmitt trigger.
I am sure a decent PCB layout could give better results but haven't branched into PCB making yet.
Don't be put off by SMD. I recently returned to PCB designing and assembling after 25 years of avoiding it. Nowadays design is easy, and SMD is remarkably easy and doesn't require expensive equipment. I now prefer it to through hole components.
You can get excellent free PCB/schematic programs, and 10 5cm*5cm double-sided through hole plated boards with silk screens and solder masks for ?10, within a couple of weeks.
There are many many guides on the web. My experiences are noted at <>
