Many thanks to SWLing Post contributor, Mike Hansgen, who shares the following article by Paul Litwinovich at WSHU:
In this article I’ll look at two things that, unless you are a serious ham operator or an absolute radio geek, you probably are unfamiliar with.
First, we will take a look at a very rare phenomenon first noted by radio listeners back in 1933. It generated several theories, but the correct one was only verified experimentally in recent times.
Second, we will look at a government-funded project that, while built for other purposes, was used to confirm the phenomenon 75 years later.
The Luxembourg Effect was first documented by electrical engineer and professor Bernard Tellegen. The professor is also credited with the invention of the tetrode vacuum tube. My past article, A Radio for the Roaring Twenties, features one of the first radios to use the tube.
One night, Mr. Tellegen was in the Netherlands, listening to a station transmitting from Beromunster, Switzerland, on 652 kHz. In the background of the Swiss signal, he could hear the audio of Radio Luxembourg, which normally broadcast on 252 kHz. He was far enough away from each station that neither station’s signal would have been strong enough to overload his receiver. The two signals seemed to be mixing somehow, but by what means?[…]
“AM occurs elsewhere in nature. A lightning strike or manmade electrical discharge will produce a burst of electrical noise that varies in amplitude. Since AM radios are designed to detect variations in amplitude, this is why they are prone to interference from such things. AM held sway as the primary method of modulating a radio wave up to WWII, not only for broadcasting, but for all types of radio communications.
Every vintage consumer radio, be it standard broadcast or shortwave, up to WWII, received amplitude modulated signals. Nowadays, AM broadcast stations are associated with lower quality audio, but such was not always the case. Receiver design really came of age in the 1930s with the superheterodyne circuit and advancements in loudspeaker design. The grand floor consoles of the late 1930s leading up to WWII were capable of producing audio that was very good, even by today’s standards, the only exception being that they were monaural, as stereo technology was still a ways off.”[…]
Litwinovich’s article is a must-read as he gives a concise overview of amplitude modulation, AM vs. FM, and even covers current proposed uses of the broadcast band (something we’ve also recently mentioned).
Zenith Model 7G605, the first in the line of Trans-Oceanic radios. Credit P. Litwinovich collection via WSHU
Many thanks to SWLing Post reader, Paul, who points out this excellent article about the Zenith Transoceanic by Paul Litwinovich of WSHU. Litwinovich’s article covers a brief history of the Zenith Transoceanic series including photos from his amazing collection (check out his model 7G605 above).
Here’s a short clip from his full article:
“The first version of Zenith Trans-Oceanic line of portable shortwave radios, the 7G605, [above] was released less than two months before the Pearl Harbor attack. It bore the sailboat image, and continued to be known as the “Clipper.” It sold for $75, and was an instant success. It was just the beginning, though, of the series’ long and colorful history. Zenith planned to heavily promote the radio for the coming holiday season. Then, the surprise attack on Pearl Harbor came. Most manufacturers halted production of consumer goods for the war effort. Zenith had other plans for their new radio, though. They changed the image on the grill from that of a sailboat to the likeness of the B-17 bomber. The change was implemented in such a hurry, that collectors have reported finding the bomber grill inserted over the top of the sailboat grill.”
Paul Litwinovich is a shortwave listener, amateur radio operator and holds a commercial FCC license as well; here’s his bio, taken from the WSHU website:
“Paul caught the radio bug as a child. By age 12, he had taught himself the basics of vacuum tube theory. He began repairing old, discarded radio sets, the kind that we now call vintage sets. He loved listening, too, to local programs, DJs who picked their own music, talk shows designed to inform, not shock the listener. But his favorite listening was to short wave radio, with its magic of music and programming from all around the world.
Hobby led to career. Paul was a design engineer and engineering manager in the broadcast industry for 14 years before coming to WSHU in 1990. He holds an FCC commercial radio license, and an extra class Amateur radio license. And, oh yes, he’s still restoring and collecting vintage radio sets, for more than 45 years now, and counting.”