I‘ve decided that during the MC3356 SA boxing (rather slow it would seem) I’d finish up the remaining circuit tweaking before I get too far along. The plot below is pretty much what I had span-wise before alteration: It shows a span of a bit under 90MHz. The harmonic blip on the far right is 80MHz. I used a 10MHz square wave source here…
After a bit of L2 coil adjustments and a few re-cal’s I was able to nudge the span up to 100MHz (wahoo!) Below find the updated plot using the same source…The blip at the right is our 100MHz harmonic.
I upped the frequency source to 50MHz and the result follows:
And then up to 100MHz (My source is a bit wonky at this frequency):
In the top plot taken with the 10MHz source notice the non-linearity setting in around 70MHz. This is due to the varactor based tuning of the VCO and having but one sweep breakpoint adjustment. All is well and I’m overall quite pleased with this project!
With this SA now basically in hand I’m going to travel a bit back in time to a micro project I had begun but left in the wake of another. In October of 2017 I posted about a Z80-based project using two D/A converters to enable writing to a scope in X-Y mode. This project was taken from an old laboratory manual which accompanied the 1981 edition of the classic text book, The Art of Electronics. Not a complex project but takes up (at least for me) quite a few solderless breadboards.
I’ve finally begun working on the schematics for the initial D/A goal and I’ll post as they get completed. The 2nd goal will be getting an SP0256-AL2 speech chip I’ve had since the 80’s integrated into this simple Z80 project. Stay tuned…
All for now…Randy