The AM Forum

While reading about the Canadian Broadcasting System RCI shortwave facility on Jim Hawkins excellent pages, I noted he described the current main transmitters thus: ASEA BROWN BOVERI (ABB) transmitters use a "pulse-step" type modulation (PSM) completely implemented in solid state and are each 250KW output. They also incorporate Dynamic Carrier Control (DCC) which causes the carrier level to be automatically reduced when there are lower levels or no audio. During periods of silence (no audio), the carrier power is reduced by 50%, so the 250KW transmitter is putting out a carrier of 125KW during audio pauses. This saves otherwise wasted empty carrier power.
Can someone tell me the difference in this theory and screen modulation OR even controlled carrier modulation?

DCC is not controlled carrier Screen grid modulation. There are a number of controlled carrier methods for broadcast.

Step Pulse Modulation was developed in conjunction with some higher powered graphite grid tubes (Pyro-Blocks) and were capable of 500kW or more of plate dissipation, similar to the Eimac 4CM500,000G and the 8974.

https://www.cpii.com/docs/datasheets/78/8974.pdf

Your question might get more views at:

https://broadcastengineering.info/viewforum.php?f=4&sid=04f4dea876dc2bb2c7a406dc26aad1aa



 

Thanks Phil, I will check that out.

Most receivers don't have the companding mentioned in the attached PDF article but it's something that can be added in the audio domain with a typical Hi-Fi audio component, if not a 'pro' component. The main difference probably being calibrated controls.

For most of us though the noise accompanying the received signal won't be too helpful! Years sgo when I was in Europe on business, the SWL to 'voice of' stations was excellent in quality. Those same stations received here are not so hot for obvious reasons.

I'm interested in listening to the music from far-off places.

In Germany back when I served Uncle Sam in 1967,68, we had a Grundig floor model radio in the office.  Everything that came from that radio: AM broadcast (especially Radio Luxembourg), SW, etc sounded wonderful.  I always wondered if it was the radio or the transmitters or both.

Back then, Grundig radios were designed quite well, and the quality was far superior to anything from the U.S.
I wish I had one now!

The only plastic in that old radio was the knobs!