Westrex Electrical Sound Recording

Today most recording is digital, just zeros and ones. But as you know, recordings began in purely an acoustic format. But in the middle of the 140 year history of recorded sound there was a great leap forward: Electrical Sound Recording. For that we can thank Bell Labs (in partnership with Western Electric). I'll get to the names in a minute but like many innovations in that shop, there is not a front man to lay the thanks on. It was a work made of a hundred small tinkering improvements, and several dozen patents. More here.

Analog phonograph recordings predate commercial radio by more than two decades. The problem with early radio was that despite all the noise, it's audio was actually superior to that of the acoustic recordings of that era. Radio was also free. Recorded sound needed a way to compete with high quality free content. Bell Telephone Laboratories was established in 1925 and set to the task.

They were not alone in trying. In the UK, Lionel Guest and Horace O. Merriman had managed to jury-rig a set of four carbon microphones to a magnetic recording head. It was a genuine electrical recording. It just sounded pretty crappy and was considered inferior to acoustic recordings of the same era. They did record at least one record on Columbia using their method in 1920. It was a recording of a service at Westminster Abbey, their gear was set up in a truck outside. But the path to a superior electrical recording, the great-granddaddy of 'em all had started years earlier. Among those advances were the condenser microphone (1922), the vacuum tube (1857),  matched impedance systems, and the recording head of course... putting it all together was no small feat. More here.

At Bell Labs Harvey C. Fletcher oversaw two teams working towards the project. Of particular interest is the matched impedance sytem developed by Joseph Maxfield and Henry Harrison. It used a complex set of electrical filters. Another engineer, Harold Arnold, made a series of improvements to the triode vacuum tube to improve it's sensitivity and linear response. These two changes alone improved audio so that it could be reliably reproduced from about 50 Hz to 6,000 Hz. Acoustic recordings of that time only eeked out a mere 250 Hz to about 2,400 Hz.

The final improvement was to improve the existing magnetic recording head technology. The existing acoustic methods relied upon the physical power of the sound wave. Here the condenser mic was used to receive that audio data, and convert it into electrical energy. The electromagnet-stylus assembly converted this back into movement. At the end the could produce a flat response from 250 Hz to about 15,000 Hz with this system. This "Western Electric electrical recording system" was branded as the "Westrex" system.

Bottle of Magic

This video "Bottle of Magic" follows the development of the vacuum from John Fleming thru the Audion at the hands of Lee de Forest, and the work of Thomas Edison's staff. It stops with the work of Bell labs of course.

Sunspots and your radio

Seeing as this is a quickly impending reception problem I thought I'd talk about sunspots. It's easy to get lost in the science behind radio wave propagation, (I get lost myself) but there are a few simple rules of thumb you can use to help understand the basics.

...A little history first: Back in 1928 a physicist named Karl Jansky was working on this new fangled technology called radio telephony for Bell labs. At the time, Trans-Atlantic telephone connections (via radio) suffered from interference caused by several things, one of which was a mysterious phenomenon called "magnetic storms." These could disrupt service for days. Nobody knew what caused it, or when or how.

Jansky was not very experienced in radio but took his task seriously. By 1931 Jansky was making regular observations of radio static at a frequency of 20.5 MHz. He identified three basic types of static:
1. Nearby thunderstorms

2. Distant thunderstorms

3. A faint steady hiss of unknown origin.

Jansky spent over a year investigating the third type of static. It rose and fell once a day, leading Jansky to think at first that he was seeing radiation from the Sun. Some of the radio static he observed came from a fixed point in the sky, and it moved! Ultimately he figured out that the source of the cosmic radio noise was our galaxy itself.

So here's where this relates to your radio. You are all aware that AM radio waves (distant ones at least) bounce off the atmosphere as part of their normal propagation. These layers are ionised by radiation from the sun. About every 10 years the sun enters the "solar maximum" a part of its normal cycle when solar activity is high. This increases its output of radiation and a specific layer of our atmosphere, the ionosphere becomes very dense. The good news is that many radio waves from space bounce off and do not cause us interference. The bad news is terrestrial radio stations and other sources of static are trapped inside the ionosphere and cause a great deal of interference. [janskys observations could never have occurred during the maximum]

During a solar maximum the number of sun spots is high, and during a solar minimum the number of sun spots is low. We are entering a solar maximum. This is measured in units of solar flux. Solar Flux is related to the number of sunspots, and affects which frequencies of noise are generally audible. Solar Flux doesn't generally go below about 70; if it's below 100, lower frequencies will work better than higher frequencies. If it's above 150, higher radio frequencies will open.

Then there is the K-index. It's released every three hours by NOAA, and it varies between 0 and 9. If the K-index is 0 or 1 for a few periods in a row, you can expect to hear stations that are normally weak or in someway problematic at somewhat stronger levels. You may hear a few stations that are normally inaudible at weak levels. If the K-index is between 2 and 4, conditions are pretty much normal. If the K-index is 5 or above, there's a geomagnetic storm. The higher the K-index, the more disturbed conditions are. You can check it here. You can also get them on WWV. They broadcast them at 18 minutes past every hour here.