[Boatanchors] Modern AM Modulation techniques

[Gary Peterson]

When Rob said about (nearly) 90% efficient, this specified efficiency is 60 Hz AC to RF !

I still maintain five solid-state AM broadcast transmitters.

One is a Harris DX-25 (25 kW output), of which the design is based on Hilmer Swanson’s patents.

One is a Nautel ND-1 (1 kW output).

The others are Broadcast Electronics AM-6As (5 kW output).  Essentially pulse-width modulation.

I won’t go further into the modulation schemes, other than to say the Harris is a totally digital modulation scheme.  At any instant, a certain number of “power blocks” are turned on or off.  

The B.E.s are modular, containing modulator boards and RF amplifier boards in each section.  The outputs are then combined.

I don’t see either of these designs finding their way into amateur gear because modules tend to be optimized for certain sections of the broadcast band.  I couldn’t use a module from a 920 kHz transmitter in an identical transmitter, used on 1380 kHz.  Various RF component values differ.  

Unless...you wanted a single band AM rig for, say 160 meters.

There are no tube-type AM rigs being currently manufactured and sold, that I am aware of.

One of the last great tube rigs was the Collins 828E-1 (later Continental 315R-1), both known as the “Power Rock.”  Pulse width modulated.  Sounded absolutely super.  Extremely reliable.  I loved that transmitter.

None of the solid state transmitters that I have dealt with are damaged by running into a funky load.  They just quietly fold back if a capacitor shorts out in the antenna coupler at the tower.

Gary, KØCX   


“The master mind for this design was now deceased Harris engineer
Hilmer Swanson.  These rigs are about 90% efficient.
Rob
K5UJ”