5. The Synchrodyne

Synchrodyne Schematic [6K]

The simple synchrodyne arrangement published by the present author in his first 1947 article was as shown in block schematic form in Fig.7. A typical circuit arrangement published later is shown in Fig.8. This is clearly quite different from Colebrook's original homodyne, and the name "Synchrodyne" was chosen for it as being very descriptive of its method of operation. However, it is quite clear from the account of the history of the homodyne given above that the original homodyne had been gradually improved until almost all the desirable features mentioned by the present author had been incorporated; the synchrodyne was, in fact, only an up-to-date homodyne. The true position may well be as nicely summarised by a French journal which reported (literal translation) as follows:

"lt is possible that the principle of the synchrodyne is not new, but it is, to our knowledge, the first time that this principle has been applied in practice and that a report of practical trials has been given"

However, these questions of originality interested only the very small minority, and did not affect the enthusiasm which was shown by the great majority of interested readers, both amateur and professional. But although this enthusiasm gave the author a great deal of work (and some satisfaction), it did not lead to any important developments in the technique of synchrodyne or homodyne reception. The letters and articles which were published by various people in several countries did not disclose any previously unrecorded principles, and there is therefore no point in examining them here; they are, however, listed in the Bibliography.

Typical Circuit [16K]

Notes on letters in diagram :-

(a) The value of C9 should be adjusted if possible to give the minimum leakage of the oscillator output back into the r.f. amplifier.
(b) This meter serves as a tuning indicator, and to check the operation of the network C.
(c) Tuning-whistle suppressing network. The choke L2 should have upwards of 100 henrys inductance and will probably need a magnetic screen to avoid 50-c/s pick-up.
(d) Cathode-follower in synchronizing path to make oscillator fre~quency independent of setting of VR3.
(e) Output to earphones --or to power stage for loud-speaker direct from anode.

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Last updated
17th September 2001