Hi all, I had some down time so sat in the workshop and on a prototyping chassis put together the circuit from "Radio and Hobbies" September 1963, a year I remember so well! (steady job, car, girlfriend what could go wrong?)

I'll send a pdf to Brad with the story of how it went, a short story actually as it did not go well, but at least I understand the shortcomings and a way forward to a better solution.

The R&H boys may have gone the next step, but locked into "superhet" thinking and with no advantage in the Synchrodyne design it was never going to happen.

Fred.

The Sychrodyne AM Tuner

with no advantage in the Synchrodyne design it was never going to happen

But it lives on as the PLL.

Document uploaded.

Yes, GTC and that will be part of the fun, making a reactance valve circuit do a PLL action.
No, I am not looking at using any transistors or chips and that's that.
Valves or nothing!
Fred.

Fred, how's this for an idea to make the Synchrodyne into a practical HiFi AM receiver?

1. Take an ordinary superhet, preferably one with an RF stage.
2. Connect the Synchrodyne circuit to the output of the mixer in parallel with the existing IF, bypassing most of its selectivity.
3. Have the existing AGC control the "RF" stage of the Synchrodyne.
4. Have the AGC switch the audio output between the normal AM detector and the Synchrodyne, so that its output is only heard when it's locked and working properly.

Once it's set up, the Synchrodyne should not need to be fiddled with. You might be able to hang your existing hardware off a suitable donor radio. Maybe make it a plug-in adaptor?

Hi Fred,

Until now, I have never bothered to understand how an AM Synchrodyne Tuner actually works ... so I always use your Special Projects write-ups to extend my knowledge ....

If I understand the theory correctly ..... in your Fig 3, one would expect to see none, or little, of the Audio signal (modulation signal) riding on the Oscillator RF(blue) signal ..... ?????

.... hence the need to isolate the Oscillator as much as possible ..... ????

Can you see the RF (carrier) signals 'locked' in phase (ie with a change of Scope scale) ....... ?????

Cheers,
Ian

Ian. maybe I can explain it simply:

You have two signals at the anode of the mixer bottle, they are the same frequency and in phase.
What you see on the anode is the sum (or difference) of the two signals.
One of those signals is modulated and so the summed signal is also modulated.
When you filter out the RF you are left with the modulation component, i.e. the audio.

Hi Tinkara, what Ian Rob says is it in a nut shell.
If you mix the station signal and oscillator signal you get selective tuning. Then filter the RF and the AF is left.
The theory then was who needs an IF stage, less valves and coils etc, but in practice does not hold true.

In the paper, fig 2 is swept at RF rate so the jumbling multiple wave shapes are created in the CRO as the time base trys to lock onto the RF and AF varying components. If you remove the AF modulation on the signal you then see steady plain RF waves and can see the phase difference .

In fig 3, this is swept at lower speed and the AF modulation is the sine shape of the RF signals. The blue trace should not be modulated but cross coupling was "squegging" the oscillator and making it look modulated as well, thus showing one of the short comings of a too simple circuit.


Sorry about delay in answer, has sudden heart failure on Monday, ambulance ---hospital...cardiac ward......stabilise…..back home today Friday!


Fred.

Good grief Fred ..... no apologies required ... I hope that all is okay with you again. I seem to remember that this is not the first of this type of episode for you ..... ???

Take your recovery seriously .... soak up up the TLC ....

Cheers,
Ian