29-06-2012, 12:11 AM
Hi Lawrence,
When it comes to R.F. stuff, I love a challenge! And to me, the objective of producing the necessary local oscillator drive signals for your receiver presents exactly that. So I had a think about the basic and the essential requirements for those drive signals.
(1) for satisfactory ssb reception, the stability of the local oscillator must be of a high order: that implies full crystal control.
(2) If you need your receiver, with its regenerative and tunable detector stage, to tune over a wide freq. range, it will need many injection frequencies.
Those two considerations really point us towards a synthesizer approach, but I hear what you say about keeping things as simple as possible.
So I've come up with my idea of a poor man's frequency synthesizer: 3 crystal oscillators, one harmonic generator followed by a LPF (cut-off at 6.5 MHz), one double-balanced mixer, 3 untuned buffer amplifiers, 4 manually-tunable L/C ccts. and some multi-pole, multi-way switching. The result is an L.O. drive signal, selectable from 1 → 26 MHz, fully crystal-controlled, so that your receiver will tune from 1 → 29 MHz. But it isn't simple - sorry! (What was that about no such thing as a free lunch?
).
The block diag. is at the bottom. A few comments: the H.G. has to produce harmonics of the 1 MHz osc. only up to 6 MHz: hence, the LPF at 6.5 MHz. The 4 L/C tuned ccts. are manually adjusted according to the required L.O. freq.
And I think that this drawing tells you the rest:
[attachment=5314]
Al.
When it comes to R.F. stuff, I love a challenge! And to me, the objective of producing the necessary local oscillator drive signals for your receiver presents exactly that. So I had a think about the basic and the essential requirements for those drive signals.
(1) for satisfactory ssb reception, the stability of the local oscillator must be of a high order: that implies full crystal control.
(2) If you need your receiver, with its regenerative and tunable detector stage, to tune over a wide freq. range, it will need many injection frequencies.
Those two considerations really point us towards a synthesizer approach, but I hear what you say about keeping things as simple as possible.
So I've come up with my idea of a poor man's frequency synthesizer: 3 crystal oscillators, one harmonic generator followed by a LPF (cut-off at 6.5 MHz), one double-balanced mixer, 3 untuned buffer amplifiers, 4 manually-tunable L/C ccts. and some multi-pole, multi-way switching. The result is an L.O. drive signal, selectable from 1 → 26 MHz, fully crystal-controlled, so that your receiver will tune from 1 → 29 MHz. But it isn't simple - sorry! (What was that about no such thing as a free lunch?
).The block diag. is at the bottom. A few comments: the H.G. has to produce harmonics of the 1 MHz osc. only up to 6 MHz: hence, the LPF at 6.5 MHz. The 4 L/C tuned ccts. are manually adjusted according to the required L.O. freq.
And I think that this drawing tells you the rest:
[attachment=5314]
Al.
