in-dash cd player with GOOD AM reception

[MikeMason]

Life's too short to listen to static. XM....

[Rick Denney]

It is a stock AM radio, no FM, no CD, no cassette, no clock, no nothing. The reception of these is supposed to be somewhat better than the AM part of most multi function units as the ferrite antenna bar in the unit is quite a bit larger with a lot more copper thread wrapped around it. It also uses the car antenna. (I am not sure about this stuff. I looked this up on the web but have not opened up the unit to confirm it. The case is a tall one (like on all Jeeps) and has a LOT of unused space, so a very large ferrite bar is a possibility.

Naw, the old OEM-style AM car radios didn't use a ferrite bar antenna. That's home stereo stuff, and even then it doesn't work very well, in my opinion. Ferrite-bar antennas are similar to electrically loaded trap dipoles, and are directional broadside to the ferrite bar. They are impractical in a car because of their directionality. Also, the shell of the car provides an RF shield that will prevent good reception for radio antennas inside the shell.

The wavelength of broadcast AM is about a quarter of a mile, so the bigger the antenna, the better, if it's sensitivity you want. (In contrast, the wavelength of FM is about 10 feet, and the standard 31" stick antenna can be a resonant quarter-wave ground plane, with the car acting as the ground plane. But those high frequences won't bounce off the sky like AM will, so it's line-of-sight only.) A good, exterior whip antenna will always work better in a car than a coiled anything inside the car.

The sensitivity of AM radios of old is a lot better than for newer radios, where the RF front end is usually stuffed onto a chip as an afterthought. That's why the old OEM-style AM radio is still likely to be a better performer than modern radios.

But sensitivity can work against you. At night, RF of this low frequency (around 1 MHz) will bounce off the ionosphere. That allows you to hear distant stations on the sky wave, but it also allows you to pick up distant noise, such as static discharge (aka, lightning). At night, you want to reduce the sensitivity to lower the noise level, and then increase the audio volume to improve the signal level. You end up with more signal and less noise.

Some radios have a "local" switch that works on AM. That reduces sensitivity at night. Sometimes, clipping the end of the antenna back to ground with a jumper will also work, and that bit of wire flapping in the breeze has a real Blokian look to it.

You may still have trouble getting a good signal from local stations at night if you are over the horizon from them, because their signals are skipping right over you. In the daytime, they can crank up the power to compensate for this, but the FCC makes most of them back down at night (and some stations even must go off the air) to prevent them from producing an excessive sky wave that will interfere with other stations on the same frequency in distant cities. The exceptions to this are the "clear channel" stations (so designated by the FCC and NOT to be confused with Clear Channel Communications), which are allowed to run the full 50 kilowatts of power at night. They can also run an omnidirectional pattern. Other stations are required to use a multi-tower array and they phase the towers to null out transmit power in directions where they might interfere with other stations. They often have a different directivity pattern at night.

The only real hope for such stations is to use a directional antenna that has good gain in the direction of the desired signal and negative gain in other directions. That also improves the signal/noise ratio. The loop antennas that you put in home AM receivers work this way, but a directional antenna is impractical in a car.

I don't know of any new radio, particularly with a CD player, that has a good AM receiver. I have one of those cheapie Pioneers with the removable faceplate, and the AM receiver in that radio is dreadful compared to the OEM radio in my Subaru. Maybe the high-end radios have good AM reception, but you could pay for quite a number of months (or years) of XM before you spent more than a high-end car radio.

The Blokian solution seems to me to be an AM-only radio from, oh, a 1967 Mercury Colony Park station wagon, and sit it on the floor. Then, put a CD/FM stereo in the dash.

Rick "noting that noise sources that will affect medium and long wave RF have increased dramatically over the years" Denney

[Tom Mason]

When I have looked at replacing the radio in my older chevy pickemup or the really old Ford that I used to have, I went to the salvage yard and picked up a stock nit from a wreck. I did this for a 98 Sierra with an AM/FM CD player in mint condition for $75.00 once. Worked great. Have seen radios from the 70's in some shops around my area.

Tom Mason