I usually cut PC board material with tin snips. A hacksaw also works,
but it makes a lot of irritating dust.
In the schematic you mention, the "a" and "b" capacitors form a voltage
divider to control the amount of signal that's fed back to the active
device. If there's too much (a/b ratio too large), the waveform will be
distorted and the temperature drift will probably increase. If there's
too little, the oscillator will be slow to start or won't start reliably
or at all.
I don't want to answer your question about calculating the oscillation
frequency without some detailed thought, which I don't have time for
just now. But I believe you're doing the right calculation. Note that
the oscillator output is in parallel with the "b" capacitor, so any
capacitive loading on the oscillator will lower the frequency. The RFC
and your inductor will both present some stray C. It's nearly impossible
to tell how much C your inductor will contribute. There are a couple of
ways to measure it, but if you've got the other capacitances under
control, you've already made yourself a test fixture for determining
inductor capacitance (assuming you know its inductance) -- it's the
oscillator.
Roy Lewallen, W7EL
Jock Cooper wrote:
Roy Lewallen writes:
When you get _Experimental Methods. . _, look at the very first few
pages -- "Getting Started". You'll find a nice drawing and some other
information about "ugly construction".
Incidentally, the method was first described and the term coined in
the article "The Ugly Weekender" by Roger and Wes Hayward, in August
1981 QST. If you can get hold of a copy of this article, it has more
about the method, as well as some other good information.
If and when you do eventually decide to get a scope -- I've been
surprised to see Tek 465 scopes going on eBay for about $200. That's
an awful lot of bang for the buck.
Roy Lewallen, W7EL
Well last night I took some double sided copper clab board and cut off
a small square. (By the way, what is the best way to cut this stuff?)
I rebuilt the oscillator on there in 'ugly' style. And it was in fact
quite ugly. It looked like something I would have done as a kid. But
it worked! Now I'm sold on it. Hopefully I can get some pointers on
improving my technique from the book.
Now I have a new question though. The circuit is a Clapp based on the
MPF102 JFET. When I compute the frequency range, it is close to the
measured range but not the same; but there appears to be some
capacitance that I can't account for, and its value seems higher than
would be 'stray'.
The circuit I'm using is basically like the one at
http://www.electronics-tutorials.com...scillators.htm
in figure 2, but without the extra parallel stuff on the variable cap.
So I calculate the cap value by adding the var cap value in series
with the caps labelled on that website as cfb-a and cfb-b. (By the
way, what happens if those two aren't the same value?) Do any of the
other capacitors in the circuit factor in?
How much capacitance could my 'pill bottle inductor' be contributing?
I was careful, but not extra careful when winding it.