I was wondering if making a low frequency RF circuit on a breadboard is viable.
In my experience, yes, but you may need to take a few things into account.
- Some breadboards are better than others. The maximum frequency I've seen operating cleanly and reliably on a breadboard is 2 MHz. I've also seen breadboards that couldn't handle 200 kHz.
- You need to consider the maximum frequency present on the breadboard, not the largest "fundamental" frequency. For instance, a square wave signal (such as a clock or the 555's output) have very large harmonics up to maybe 5 or 7 times their fundamental frequency. If the breadboard can't handle these, then the clock will become distorted (low-pass filtered); additionally, if those harmonics spread through the breadboard, they'll distort potentially all your signals.
- Bypass capacitors become important as the frequency increases. Put one cap everwhere a circuit connects to the supply or ground, and you may have to sprinkle them around wherever high-frequency harmonics appear.
If you are insanely attentive to layout, yes. That means:
- Bypass everything with as short of wires as you can,
- Lay your wires down flat on the board (which pretty much means you'll be doing a lot of bending and possibly custom-cutting of wires). Big loops will kill you for sure.
- Be willing to use twisted-pair, or even small coax to go from one "major" stage to the next (i.e., if you're putting multiple breadboards together, use transmission line).
- Position your components so that the sensitive connections are short.
- And, of course, everything that I left out.
Actually, in the early days of radio when RF was below 500,000 CPS *** , most gear was built on a wooden breadboard with no concern for stray coupling. And it worked (sometimes). Good luck with your Branley coherer and watch out for the wouff hong.
*** CPS is a unit of frequency named for Charles Proteus Steinmetz.