Archimedes said:
Hi Dave
I just built a superregen receiver. It is excellent. I can pick up
FM and Air Traffic !!!
Of course a superregen is just an extension of the basic regen.
A regen is an amplifier with positive feedback, or an oscillator with
controlled oscillation, depending on how you view it. The incoming signal
goes through the amplifier, comes out stronger, and gets fed back to
the input of the amplifier, where it gets amplified again, and so on.
Howard Armstrong got a patent on the idea, and at the same time as
inventing a receiver that was far better than already existed, in 1914,
he showed how tubes could be used as oscillators (which was a big jump
to, so those spark gap transmitters and alternator transmitters could
disappear).
But, it's finicky. The point where the most gain and selectivity occurs
is right on the verge of oscillation. That means a pretty unstable circuit,
and every time you move your hand near the regen or the antenna sways in
the wind, or the voltage varies, the regen can kick into oscillation, leaving
terrible squealing in your ears. IN some cases you want that oscillation,
to beat against an incoming signal, but you don't want it to happen
unexpectedly.
The regen however provided lots of gain in only one stage, and while it
had its limitations, so did the crystal radio (no active components) and
the TRF receiver (multiple tuned gain stages on the signal frequency, also
prone to oscillation).
Armstrong's next Big Invention was the superheterodyne receiver, the
patent was issued in 1920. Far more complicated, it beat the incoming
signal down to a fixed frequency where gain (and later selectivity)
could easily be had, not just because it was at the time lower in
frequency, but nothing needed adjusting in those gain stages after
alignment, unlike all the other receivers that often needed adjustment
every time you changed frequency.
Howard's regen patent was challenged, so he ended up in court. Just
before the trial started, he hooked up his regen receiver to refamiliarize
himself with the operation, and noticed an oddity that he had noticed
when he'd originally played with the regen receiver. ANd that's when
he discovered the notion of superregeneration, which he got a patent
for in 1922.
The superregen is a regen receiver. The only addition is something to
modulate the regen stage at an ultrasonic rate. It can be an external
stage, that makes visualizing what happens so much easier. Or, far
mroe common is the active stage of the regen detector is called upon
to oscillate at an ultrasonic rate in addition to acting as the regen
detector. This pulsing allows the regen detector to be on that verge
of oscillation where the gain is the highest, but always pulling it
back from there so it doesn't go into oscillation. It becomes a more
"stable" circuit, requiring no regeneration control or any other control
other than whatever is used to adjust frequency.
There was a time when you'd see regen receivers described and they
were treated as both regen and superregen, since it was only a minor
change, and done properly the same regen control that set things on
the verge of oscillation or into oscillation if that was desired, could
be turned up another notch and set the thing into oscillation at an
ultrasonic frequency and hence it becomse a superregenerative detector.
So Armstrong created three receiver schemes that were and remain the
three basic types of receivers over the years. Regens fell by the
wayside decades back, though their simplicity makes them useful
for project building. The superegen never really saw that much
commercial broadcast use, but it saw plenty of use at the higher
frequencies, and of course saw lots of use in cheap walkie talkies
and garage door opener receivers over the years, I gather right up
to the present.
The superhet had a slow start, it was useful but required all those
tubes. But of course, it really won out, virtually any radio or
tv set uses it. Only in recent years has any strong contender come
along.
Michael
