Electric Vehicle Radio
April 11, 2012 Nowadays, it's rare when someone listens to AM radio, but it was the only option a few decades ago. In those days, before ubiquitous FM radio, CD players, and digital music players, it was the only way to hear music while you were driving. No one seemed to notice the low fidelity, a result of the bandwidth of such stations being capped by their 10 kHz channel spacing and the bandwidth of the intermediate frequency (IF) stage in their superheterodyne receivers. There was also the noise. Nature is noisy in an amplitude-modulated way, so AM radio reception is noisy. The prime example of this is lightning noise that can be heard during thunderstorms. In an automobile with an internal combustion engine, the electrical spark ignition will generate noise. This is less of a problem today with electronic ignition. It was a problem with the older, mechanical, distributor-type ignition systems, which had a greater density of sparks than a 4th of July celebration in the US. Music eventually migrated to the FM band, where there's more bandwidth and an easy analog method to broadcast stereophonic signals. FM has the further advantage that frequency modulated noise is rare. This advantage may disappear with the introduction of electric vehicles. The high currents and specific control circuitry for their motors can cause significant electromagnetic interference that includes both amplitude and frequency modulated components. | The First Electric Car? Electric car of Ányos Jedlik, 1828. Jedlik was an Hungarian inventor, engineer, physicist, Benedictine priest, and a member of the Hungarian Academy of Sciences. (Via Wikimedia Commons). |
"The size and position of individual components – including the electric motor, the battery, the air-conditioning compressor, the charging system, the DC/DC converter and the frequency converter itself – play a crucial role. How and in what direction cables are installed is just as important, as is the thickness of their insulation."[FR]All this reminds me of the vacuum tube days, when signals from the 6.3 volt (rarely, 12.6 volt) filament supply would introduce 60 Hz hum into audio amplifiers. The mitigation scheme was to twist the filament cables before connection, so that the induced currents canceled, keeping these wires well away from sensitive components, and not have other wires run parallel to filament lines. Other tactics were to have a grounded center tap on the transformer winding that supplied the filament voltage, or wire in a "hum pot." A hum pot was a low resistance (typically 100 ohm) potentiometer connected across the filament supply with the wiper attached to ground. Suitable adjustment of this potentiometer would allow phase cancellation of the spurious hum signal. Fraunhofer has further redesigned the power module, a component of the voltage converter, in a symmetrical architecture which will further reduce interference.[FR] The German researchers point out that such interference problems are not limited to electric vehicles. Photovoltaic arrays have similar high currents and electronic circuitry, and their placement atop residences would cause interference within. To hear the radio frequency interference emitted by my LCD monitor at 250 kHz, listen to this ten second MP3 clip.
References:
- Chevy Volt FAQs, GM-Volt.com.
- Early MP3 Patent Enforcement, ChillingEffects.org. Muzinée Kistenfeger, The Fraunhofer Society (Fraunhofer-Gesellschaft, FhG), Science and Innovation Factsheet No.5, British Embassy Berlin, July, 2007.
- Listening to the radio even with an electric drive, Fraunhofer Society Research News, April 2, 2012.
- Early MP3 Patent Enforcement, ChillingEffects.org. Muzinée Kistenfeger, The Fraunhofer Society (Fraunhofer-Gesellschaft, FhG), Science and Innovation Factsheet No.5, British Embassy Berlin, July, 2007.