Interesting Richard, thanks.

I read about these early pioneers years ago when I first became
interested in ham radio and was fascinated by the history of early
radio. There was a recent PBS program on the topic too, which I very
much enjoyed.

Regenerative receivers are all that you say they are, and more. If it
wasn't for the blasted gain control which has to be constantly
twiddled, they would be more popular today I'm sure. Don't they have
limited ability to separate the individual sidebands though, so they
are more suited for AM and very narrow bandwidth CW?

I'm intrigued however.....

Lately I've been working with a QSD based receiver and am very
impressed with it's simplicity and degree of performance. There are no
non linear mixers, IF's, detectors or IF transformers, so high
performance receivers are quite simple to build using this technique.
In general, no rf stage is needed (or desired). All of the 'gain'
comes after the detector, which is actually a high speed analog
switch. But, recovering the audio without DSP based software (usually
a sound card) is very difficult, needing large amounts of selective
audio filters slowly tailor the audio response to an appropriate
selectivity. Maybe some regeneration could be used to simplify this
fairly complex analog filtering.

N7VE's high performance direct conversion receiver (the NC2030) has a
highly detailed explanation of the post QSD audio using a hardware
approach rather than the more typical computer/sound card approach.

It's good reading if you're interested in clean sounding cw without
ringing and without over processed audio filtering crud mixed in..

While the job is simplified by modern op amps, it still takes a lot of
stages of low Q filters to make the audio sound clean and crisp. A
single high Q audio stage doesn't work well at all.

I wonder if regeneration could be implemented to simplify the
complicated filtering needed to produce clean output from QSD based
receiver?

I'm also wondering whether newer technology can automatically control
the regeneration as needed, which might give a technological boost to
an old concept and revive it in the process??!! It's happened before
(example is newer high performance phasing type receivers are much
easier to build with op amps and offer much higher performance in an
easier to build package).

I might try some regenerative feedback in some of the post detector
audio stages next time i have the radio on the bench.

Thanks,

Tra







On Sun, 30 Oct 2005 16:37:57 -0600, (Richard
Harrison) wrote:

TRABEM wrote:
"I didn`t price it yet, but I need more technical information!"

There`s a better approach than high "Q" capacitors for a VLF loop. It`s
been available since the year 1912 and much used soon after its
invention.

Edwin H. Armstrong, 1890 - 1964 was radio`s most productive inventor. He
invented regenerative control in 1912. I think he awakened his sister in
the middle of the middle of the night screaming : "Eureka, I`ve found
it!" or something to that effect. It wasn`t ubique for Howard Armstrong
to discover things. Following controlled regeneration, he discovered the
principle of the superhet in 1918, superregeneration in 1922, and the
complete system of frequency modulation in 1933. He would battle RCA and
Sarnoff for his entire life over control of his discoveries. I recall
seeing a photo of the battery portable radio Howard built and gave his
bride as a wedding present on an IEEE magazine cover.

Ever since 1912 there have been regenerative circuits introducing a
fraction of a receiver`s output back into its input to enhance its
amplification and sharpen its selectivity. Some of these are called "Q"
multipliers.

A "Q" multiplier is an oscillator circuit which has its regenerative
feedback adjusted just below the point of oscillation. It amplifies the
signal many times and shrinks the apparent bandwidth the tuned circuit
accepts. I`ve seen them used for reception of WWV at Boulder on 60 kHz
and for other low frequencies. This seems easier than using super parts.
Use some positive controlled feedback in the loop circuit. Adjust it for
convenience.

Best regards, Richard Harrison, KB5WZI