Microwave Tube Modulation

[Fusionstate]

I believe I've figured out how a magnetron is modulated in microwave transmissions. The output is pulse width modulated by turning the cavity voltage on and off. You should also be able to modulate the output power by dropping the high voltage.

Is that right?

 

[nomadradio]

I remember a guy back in the 90s who modulated the DC power to a microwave-oven magnetron to transmit FM analog video. Gave a slide presentation at the ATV meeting during the Dayton Hamvention.

Any time you modulate an oscillator, you'll get FM. Don't think he modulated the carrier's amplitude all that much.

Seems to me you would be chasing the frequency of that signal to use it that way. Don't remember ever seeing a description of his setup in print.

But that's the closest I have ever come to modulating a magnetron.

73

 

[brandon7861]

I saw an article on Am modulating by altering the axial magnetic field, but my brain cannot process such complicated things. I have a different idea.

Why not use a wave guide to couple CW energy into an antenna array that has elements electronically switched at an audio (or whatever) rate such that the antenna pattern moves? The load on the magnetron remains constant, only the directivity of the array is altered. Would that not simulate AM modulation in a given direction??? Make the pattern of an electronically steerable antenna rotate/shift at a speed proportional to the modulating signal.

If efficiency is not a concern, just throw away half the power and put a few circulators in line with dummy loads to deal with reflections, and then electronically de-tune a fixed-direction beam.

Rotational Modulation, Patent pending lol.

 

[Fusionstate]

I saw an article on Am modulating by altering the axial magnetic field, but my brain cannot process such complicated things. I have a different idea.

Why not use a wave guide to couple CW energy into an antenna array that has elements electronically switched at an audio (or whatever) rate such that the antenna pattern moves? The load on the magnetron remains constant, only the directivity of the array is altered. Would that not simulate AM modulation in a given direction??? Make the pattern of an electronically steerable antenna rotate/shift at a speed proportional to the modulating signal.

If efficiency is not a concern, just throw away half the power and put a few circulators in line with dummy loads to deal with reflections, and then electronically de-tune a fixed-direction beam.

Rotational Modulation, Patent pending lol.

What you're describing sounds like, Phase Array Radar. The pulse is steered, did I just describe cattle? The transmitted pulse is caused to leave the antenna at a varied angel by phase shifting the array. That is why modern nave ships no longer have the rotating antenna.

 

[brandon7861]

What you're describing sounds like, Phase Array Radar. The pulse is steered, did I just describe cattle? The transmitted pulse is caused to leave the antenna at a varied angel by phase shifting the array. That is why modern nave ships no longer have the rotating antenna.

Except in this case, the rotation causes the same signal in all directions simultaneously. The trick would be to get the pattern shaped just right so that when it rotates (say at 1kHz), the amplitude at the receiver changes in a sinusoidal manner to reduce distortion. Making the nulls and lobes of roughly equal width would be the tricky part, especially since nulls are usually sharp and lobes are usually broad.