wait a minute. is that a tuner or a tank?

[Opcom]

I found this circuit (1) in August 1952 QST, page 11, and it is listed as an automatic antenna tuner. It seems straightforward regarding the phase discriminator, but look at the tank there. The feed from the transmitter is from a 40FT coax, which at the transmitter is fed by a link on a traditional push pull tank. He says it works from 3.5-14MHz. The dipole is connected to taps on the coil where it says ant tank.

I got interested in studying it in conjunction with reading the MB-4 and MB-150 multiband tuner articles and tried drawing an adaptation based on (2) JAN 1954, page 11, QST transmitter using a modded MB type tank. automatic tuning..

Then I realized I don't see an antenna tuner, it looks like a tank circuit. And then, why would the discriminator shown tune this properly unless it was real close to begin with. And why bother then. Just trying to understand. I can't really post the whole material as it's copyrighted but it can be seen in TIS.

The type of discriminator there, it is seen in self tuning circuits where the main issue is phase error, not frequency error in the circuit to be tuned, and also in those circuits where it powers a meter and the operator nulls the meter.

I do not see how it would work for example if the tank were set to 4 MHz and the frequency was 10. There would be very little signal and the error would not be 360 degrees of phase but millions of 'rotations' to go through from 4MHz to 10. It needs an amplitude discriminator too. ??

Back to the original diagram, is that an impedance matcher or a frequency tuning circuit?

[k4kyv]

In the top one it looks like it could be either one.  You have a tuned circuit, and the device detects the phase error, which nulls out at resonance.

In the bottom one, there is no separate antenna tuner.  The antenna coil is coupled directly to the tank coil, without a coupling link between them.

[KA3EKH]

Discriminator circuits were all the rage in the fifties, not in Ham stuff but in military applications. The old Collins 618S and ARC-38 both used a discriminator for tuning the PA on its own. The 180L series automatic antenna tuners use a discriminator and that finds resonance regardless of the frequency within twenty seconds using a simple discriminator that tells if the line is above or below resonance regardless of phase so don’t think phase has anything to do with the operation, just resonance. Don’t have it handy but the T-195 schematic may shed some light on this being that used a discriminator to tune the transmitter to resonance for Z of 50 or to a high Z whip antenna, maybe the idea is just to get the tank to resonance and the assumption that once at resonance it's at the right frequency and best power? The value of XL in the tank don’t matter it's just tune for maximum power, XL will be different depending on the value of the load or antenna anyway.  The ARC-38 uses one discriminator on the PA that tunes the PA to max power or resonance and then coax between the radio and the 180L tuner that uses a discriminator on its input to control the coli and capacitor for driving the input to resonance. It’s an incredible system that I wasted about two years on to get working correctly. The manuals were almost useless in explaining it with charts and vectors but getting the things working you quickly finds out the discriminators put out zero volts at resonance and the further away the more negative or positive it gets. The biggest difference between what the military was using and your two schematics are that in military applications they used mechanical choppers and amplifiers to create a AC voltage that would vary in phase and be used in a AC motor with two windings one with a reference winding and one from the amplifier and as phase would vary +/- the motor would move in that direction. All that AC servo motor and phase mechanical stuff back in the late forties and early fifties was the work of genius and a lost art today.

[Opcom]

Have to revisit the 681S-1 and 180-L manuals online and see. Maybe there is hope for the idea of a multiband tuner. IIRC the 618 has a shielded loop neat the tank roller for a pickup.