"J Shrum" wrote in message
news
I am trying to make the Micronaut. I have put it together manhattan style
(which I find soooo much easier). I have tried using the air core and a
toroid I had...
The trouble is at this point, is the thing won't oscillate. The only
substitues I made was, instead of a 2n2222, i used a 2n3904... I also had
to
use 220pF caps instead of 270pF's for C1,C2 and C3.
I have checked w/ a freq counter, and I see no oscillation coming of of
any
test points.
Has anyone made this?
http://imagenisp.ca/jsm/Tuna.html
Thanks in advance.
"J Shrum" wrote in message
...
Greetings,
As a newbie to RF building, I have noticed that some instructions tell
you
how to wind the coil, and they give you the value of the coild as
well...
In my scenario, the inductor in question is a .72uhy which the
directions
state to use 17 turns of #30 around a toroid. I don't have the requested
toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M
ohm
resistor.
This will just the same right? Whether its a .72 on a toroid, or a .72
on
a
resistor... they are both the same, correct?
Thanks for your help.
James Shrum - KC9FFX
Oh boy. When circuits get that small they cease being "simple" and start
getting "subtle". Every componant value makes a difference. That having
been said an air-wound inductor should be OK in that circuit, because that
filter isn't very high Q to start with, so a Q=50 coil won't be that
different from a Q=75 coil.
In order for that circuit to oscillate the load at the crystal frequency
needs to look like an inductor in parallel with a not-too-small resistance.
I have _not_ run the numbers on the circuit with the values given or with
your values, but decreasing the capacitance at C2 and C3 _will_ increase the
amount of power that the antenna is trying to take from your oscillator,
which may cause it not to start. This may be your problem.
I'd start by trying 270pF caps, or putting 47pF caps in parallel with the
220s. If that doesn't do the trick start looking for a garden-variety
wiring error (I've spent days in fruitless theoretical analysis because of a
cold solder joint -- it ain't fun).
Good luck.
---------------------------------------------
Tim Wescott, KG7LI
Wescott Design Services
http://www.wescottdesign.com