For most people, an enjoyable part of driving their cars is listening to their favourite music while on the road. If an older car was equipped with a radio, it was very often an AM radio. FM radios were originally introduced in the early 1950s but AM remained the basic radio option well into the late 1970s. Today, it is hard to imagine your daily driver not even having a basic AM/FM radio and the connected car is becoming ubiquitous .
The audio spectrum (what frequencies the human ear can hear) is ranges from 20 Hz to 20,000 Hz with normal conversation taking place in the 85 to 180 Hz range for men and 165 to 255 Hz range for women. A woman's high--pitched scream can reach 3000 Hz while the highest note in an 88-key piano is 4186.01 Hz. In telephones, the usable voice bandwidth is in the 300-3400 Hz range.
For those of us with basic AM radios in our cars, it is becoming harder and harder for us to enjoy any music because the vast majority of music stations are on the FM band. AM radio stations are 10 kHz apart which means the maximum bandwidth is also 10 kHz. Therefore, the maximum upper upper modulating frequency is 5 kHz (see sideband). With AM's limited bandwidth of 10 kHz (compared with FM's 200 kHz), the available sound fidelity is best suited to talk radio and this genre is now very common on the AM band. The few AM music stations that remain are very often Adult Contemporary. The power output of AM stations varies from very low power Class D stations (50 W minimum) up to Class A clear-channel stations (often 50,000 W, like 740 AM CFZM) that broadcast for hundreds of miles. Highway Advisory Stations transmit up to 10 W. Many AM stations reduce power at night or even go off-air.
Twin-shaft OEM and aftermarket radios were common upgrades for American cars back when they were relatively new. However, new, commercially available twin-shaft radios today are limited in availability and quality. Often (at least for older Mopars), twin shaft head units don't fit well in the OEM cut-outs and dashboard modification is necessary to install them. New twin-shaft options are still available from:
Many radio repair shops offer FM conversions and this is done with the Aurora Design FMR-1 AM/FM Receiver or the Aurora FMC-1 FM Tuner. The FMR-1 will convert your head unit into a modern 180 W multi-speaker AM/FM radio with auxiliary input but requires the gutting of the original internal components. The FMC-1 adds an FM tuner and auxiliary input to an OEM radio by splicing the FMC board between the antenna lead and the radio circuitry but does not change the audio output (number of speakers or power). To cycle between AM, FM, and auxiliary input with either system involves switching the radio off and on.
Another option is to install an auxiliary input radio adapter like Brew City Engineering's RediRad. This device connects between the antenna lead and the radio and allows you to add the input from any device with a 3.5 mm headphone jack. The RediRad adapter "broadcasts" into the antenna lead at 1000 kHz so you need to tune to this frequency on your radio. When the RediRad adapter senses output from your portable device (smart phone, mp3 player, etc), it will switch over the 1000 kHz signal to your device and will switch back to the over-the-air broadcast signal within a minute after the device is turned off. Since many portable devices have FM tuner capability when used with head phones (the headphone cable becomes the FM antenna), the RediRad adapter can also add FM to your AM radio.
With the car's body being a huge Faraday Cage, the best place for an FM antenna is outside the car.
After 50 years of service, my radio needed repairs because time had taken its toll on its capacitors. Time had also taken a toll on radio stations and I was especially disappointed that some of the AM stations I enjoyed earlier (like 1050 CHUM and 1150 CKOC) are now TSN stations. However, I had found enough music-playing AM stations (ones that hadn't switched to talk or sports format) that I could still have some audio entertainment. My wife and kids weren't fans of the AM stations now on my presets and they convinced me to go for the FM tuner upgrade.
After getting my radio back from the radio shop, I took the covers off and took some photos of the new parts. The FMC-1 board is very small but, even so, it wasn't easily to find a place to mount it in the Chryco AM radio of my 1965 Barracuda
The Aurora FMC-1 includes a auxiliary input feature and the radio shop installed a pair of female RCA jacks. Since my radio has only one output for the dashboard speaker, the stereo output from my MP3 player is combined into mono sound. I bought a 6' cable with a 3.5mm male audio plug on one end and a pair of male RCA plugs on the other. I made sure that the 3.5mm plug would fit in my phone case's headphone jack hole because many jacks appear to be quite large.
I leave the RCA side of the cable attached to my radio and the other end rests on my transmission hump until I need it. The headphone cable functions as the FM antenna for many MP3 players (including my phone) and, with a relatively strong FM signal, I can use the MP3 player's FM tuner instead of the FMC-1 FM tuner even inside the car. Using the car's external antenna, the FMC-1 is a better FM tuner than my phone. It is a wonder that the phone's tuner works at all because of the Faraday Cage effect of the car's body.
If I wanted to return my radio to OEM condition, the Aurora FMC-1 FM tuner upgrade is easily removable.
