On Mar 24, 6:32�am, ken scharf wrote:
Kevin J. wrote:
I have more portable radios than I know what to do with and was
wondering if I could somehow convert one of them for use as an
extremely low-powered AM transmitter for use around my apartment. I
need only a range of 10 feet or so and I really don't want to buy any
sort of kit as Part-15 regulations in the US prohibit their use but do
allow homebuilt units. I had one of those toys called a Wild Planet
Radio DJ that was FCC type-approved but it got misplaced in my last
move and now my old-time radio shows are just sitting there waiting to
return to life on my antique radios.

Or, should doing that prove impractical, how hard is it to learn how
to solder? :-)

As a kid I fooled around with radio circuits. *I built a solder less
breadboard for building and tearing down circuits that had 4 octal
sockets and tons of farinstock clips for interconnecting parts. *I had
quit a few old tubes in the junk box when an old time radio repair man
gave me what was left of the contents of his tube caddies.

So I wound an oscillator coil around a cardboard tube from toilet paper
and built a Hartly oscillator with a 6F6G running with 300 volts on the
plate. *It was modulated by another 6F6G choke coupled to the
oscillator. *So I was running near 1-2 WATTS input. *I connected several
feet of wire as an antenna to the cathode of the oscillator tube and
tuned it to the middle of the broadcast band at an empty spot on the
dial. *A crystal phono pickup directly drove the modulator tube.

I would put on an LP record and take a transistor radio outside to see
how for out it got. *It covered the whole block! *Probably illegal
power, but I never used it long enough for anybody to notice. *Without
the antenna, I could still hear it anywhere in the apartment house.

Few in here were around when the "phono oscillator" was a
consumer electronics product...in the 1940s. :-)

Back then there were few "radios" (AM broadcast receivers)
that had any audio input jack on the back and "records"
(78 RPM discs) were the new thing for the home.
Phonographs (self-contained units) sometimes had such
oscillators...usually one-tube AM oscillators that could be
set to an unoccupied spot on the AM BC band. No wires
to connect! :-)

These were neat little projects for the teener back then,
letting them play grown-up "broadcaster." I was one of
those for a few days back then...until my Dad, coming
home from work, saw my buddy carrying my portable
receiver and listening to my voice coming out of it...:-)

Not a technically-difficult task to build one, even very
low-power. Today's wireless FM microphone is more
complex, although not too much. With transistors or
ICs, an AM wireless mike can be made, with battery
supply, in most any large microphone enclosure. No
mike cable needed.

It's USE is a fad, little more. The FM mike in a Karaoke
setup is much more entertaining in a party environment.
These "AM broadcast" thingies are good as minor profit
devices for kit makers but very limited due to today's
[USA] Part 15 limitations.

73, Len AF6AY