Question about toroid vs. air core coil.
J Shrum
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
Tim Wescott
"J Shrum" <shr...@madisontelco.com> wrote in message
news:VoudnZ0YU62...@shawneelink.net...
There will be differences in the coil Q and sheilding (toroids are
self-shielding and often have better Q than air-wound). I don't have the
vaguest notion of what your circuit is, but you can probably get away with
it, at least until you've ordered the right coil form.
Michael Black
play.
What's the application? In various wideband applications, a core material
is specified to give it broadband response.
There might be a specific reason for using a toroid, because of it's
self-shielding qualities. If you're building in a small space, it may
be counting on that self-shielding.
Michael VE2BVW
Henry Kolesnik
but while you're waiting you might try increasing the number of turns.
Experiment and improvise, that makes the hooby more intersting. Also try to
read up on air inductiors and those on toriods, I assume it;s ferrite.
73
Hank WD5JFR
J Shrum
(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" <shr...@madisontelco.com> wrote in message
news:VoudnZ0YU62...@shawneelink.net...
Tim Wescott
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
J Shrum
I did the stoopidest thing I could imagine. I wound the coils for the
20meter band, and I had a 40 meter crystal in it. :)
I must say, this little toy sings! I can't even believe how great it sounds
for having 1 transistor and a couple caps.
Thanks again folks.
DE KC9FFX
"J Shrum" <shr...@madisontelco.com> wrote in message
news:D-idnb1I95Z...@shawneelink.net...
Tom Bruhns
work. But from the numbers you gave, I guess the specified core must
be a T-20-2, no? Whatever the core, you should be able to get an
estimate of the Q that the toroid form will give you (for example, see
http://www.amidoncorp.com/aai_ironpowdercores.htm), and you can make
an estimate of the Q you'll get at the same freq with an air-wound
coil, just to be sure you're in the ballpark. For coils about as long
as their diameter, the Q is roughly 100*(diam,inches)*sqrt(f,MHz)
There are air-core coil programs around that will estimate the Q more
accurately, and the self-resonant frequency as well...Reg Edwards has
one, for example. -- If I guessed right on the toroid core, you'd
probably see a Q around 120-140 in the 5-10MHz region for your coil,
and you'd have to use an air core coil roughly half an inch diameter
to get that. (My coil program tells me that 11 turns of #22AWG 3/8"
ID and a bit under 1/2" long will give you the inductance you want, at
a Qu of about 150.)
Cheers,
Tom
"J Shrum" <shr...@madisontelco.com> wrote in message news:<VoudnZ0YU62...@shawneelink.net>...
N2EY
> Nevermind... I figured it out.
>
>
> for having 1 transistor and a couple caps.
>
> Thanks again folks.
>
73 de Jim, N2EY