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The RF Workbench / Help with 22m beacon kit from Black Cat Systems
« on: March 10, 2021, 2317 UTC »
Hello,
I ordered a 22m beacon kit years ago and finally got around to putting it together. It works great as long as my supply voltage is 4v or less - nice clean sine wave on frequency, keying from uC works. Anything above 4v, and it will tend to oscillate at a higher harmonic (and not make it through the output filter, thankfully). When I first power it up, it'll oscillate on the crystal's fundamental, but if I adjust the pot, or "key" the microcontroller (either with the actual microcontroller or manually with a wire from pin 6 to VCC or GND), the 74HC02 will jump up to a harmonic and stay there until I cycle power to the board.
Anything I can do or anywhere I should look to diagnose/fix this problem? I'm powering it off a bench supply for now, no regulator installed on the board (just jumper). No extra caps, although I played with a few values in C16 without any change in this behavior. I've checked my component placement and all looks well. I measured 4.98v in the initial voltage check prior to installing the 74HC02.
If I run at 4v or lower, it functions exactly as it should. This probably won't be a real problem since I plan on using a solar light w/ battery to power it, but I'd like to learn and understand what's happening and how to fix it.
Thanks!
I ordered a 22m beacon kit years ago and finally got around to putting it together. It works great as long as my supply voltage is 4v or less - nice clean sine wave on frequency, keying from uC works. Anything above 4v, and it will tend to oscillate at a higher harmonic (and not make it through the output filter, thankfully). When I first power it up, it'll oscillate on the crystal's fundamental, but if I adjust the pot, or "key" the microcontroller (either with the actual microcontroller or manually with a wire from pin 6 to VCC or GND), the 74HC02 will jump up to a harmonic and stay there until I cycle power to the board.
Anything I can do or anywhere I should look to diagnose/fix this problem? I'm powering it off a bench supply for now, no regulator installed on the board (just jumper). No extra caps, although I played with a few values in C16 without any change in this behavior. I've checked my component placement and all looks well. I measured 4.98v in the initial voltage check prior to installing the 74HC02.
If I run at 4v or lower, it functions exactly as it should. This probably won't be a real problem since I plan on using a solar light w/ battery to power it, but I'd like to learn and understand what's happening and how to fix it.
Thanks!