The R*G*S OCTA-MONIC

Radio Broadcast magazine of October 1927 introduced a "revolutionary" new design for radio receivers. "Not Regenerative! Not Tuned Radio Frequency! Not a Super-heterodyne! But a Radically and Fundamentally New R*G*S Octa-Monic."

The October issue outlined the principles of the design; the November issue detailed the production design. Both issues featured a two-page ad giving the virtues of this revolutionary design. Designed by David Grimes, an inventor of other unique receiver systems, the idea was to convert the received signal to one of double its frequency. Rather than using the superheterodyne principle to achieve this, a "harmonic generator" stage was added. This stage was essentially an rf amplifier biased so that its output was not linear, therefore creating harmonics, and in particular a second harmonic, of the received signal. The following stage was then designed to amplify (or detect) this second harmonic of the received signal.

The Harmonic Generator stage of the Octa-Monic receiver. The inductance of the second coil was one-quarter of that of the first. This allowed the standard ganged tuning capacitor to be used and still track across the dial.

The harmonic generator stage created considerable loss in signal strength but, according to the article, adding amplification was no problem. Accordingly, a standard RF amplifier was used ahead of the harmonic generator stage. The idea was to give greater selectivity but without the loss of bandwidth which resulted from cascaded rf stages all tuned to the same frequency. Presuming an input of, say, 1000 kHz, the output of the harmonic generator would be 2000 kHz. (Actually they used kilocycles back then with which the system may have been more practical.) An interfering signal of 1010 kHz would result in a harmonic of 2020; now 20 kHz away from the desired signal. Not only that, but the sidebands of the desired signal which might have been reduced by the response curve at 1000 kHz, would not be reduced as much at the response curve at twice the frequency. For example, a 2000 Hz audio signal would be .002% of the 1000 kHz signal, but only .001% of the 2000 kHz harmonic, and therefore not reduced as much by the slope of the response curve.

To this writer this all sounds great but my experience has been that distortion in the rf stages also distorts the audio component as well. Back in the '20's distortion was so great that a little more probably didn't make much difference. Like many of the other "revolutionary" designs of the early radio era, this one also faded into oblivion. I wonder if any of these "Octa-Monic" receivers are still around.




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