Jamie wrote:
Hi Newsgroup,

Been trying to make a regen radio out of garbage. So far, I seem to have
all the parts and it almost seems to work, however, I'm a bit confused
about the inductance of toroid cores.

I've tried to use one of those things from the back of a monitor (presumably
to prevent RF interference) as one of the coils and another adjustable coil
from another device, to no avail. It has no markings and it appears to be
a ferrite device in the shape of a ring.

Anyone know an easy way to figure out how many turns to get (presumably 300mh?)
from one of these? Can I measure it with a ruler and some how get a formula
for the number of turns / mH ? Are these really bad deviced to use? (the thought
occurs I must admit, that if it was meant to BLOCK rf, using would be illogical)

Here's the circuit I'm basing it on:

http://www.tricountyi.net/~randerse/regen.htm

If I inject a signal directly into the coil (in place of his amplified RF "front
stage") I can pick it up, but no oscillation and lousy tuning. (comes in on pretty
much 1/2 the dial) I'm assuming this has something to do with the tank circuit. (I have
two air capacitors totalling around 360pf one from a console stereo, the other from
some place I can't remember where..)

He's got 25T and 23T specified for a T-50-2 coil. Closest research on these that
I can find is that this should produce about 300mh (but I could be wrong! anyone know
for sure what the mH is on that?) This seems to make sense from everything I've read
so far, but.. I have no way to measure it.

If I end up using an air core, would I keep the ratio of turns for the tickler and
injection coil? (where he has 3 and 5 turns spec'd) ? It's my assumption that
in these two smaller coils, it's a step up transformer so it'd be a matter of ratios,
am I correct in this assumption?

Every bit of the circuit should come from garbage (the MPF102's I had to buy, but thats
it) Even the coil wire is from the transformer of a broken microwave, the LM386 chip used
for audio (and some resistors) will come from an old modem and the pot is a 500k pot,
(from a console) wired in parallel with a ~10k resistor to give a range between 0 - 10k ohms.

The main point is to build it from garbage, I already have a radio and don't
really "need" one, but.. as I once built a tube version of this (far simpler)
doing one in solid state appeals to me.

Jamie

There are toroid cores that would work quite well for this, but the
characteristics of the core depend heavily on the core material. It can
be very difficult to characterize a mystery core.

I suggest you look in the ARRL handbook for the appropriate coil formula
(or search the web) and make a single-layer air core coil on an
appropriate-sized form.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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