Very simple AM/FM antenna question... Help much appreciated!

**azzurro** · 11-08-2005, 08:29 PM

Hi all,

I have a very quick question that I couldn't find an answer for through a search.

Is there typically a separate gain stage for car radio antennas? i.e. Is the RF signal that is being picked up by the antenna amplified before being processed by the rest of the circuitry in the headunit, or are these radio stations blasting enough RF power that the car radio antennas don't need any gain?

I'm sorry if some of you perceive this as a stupid question, but I need to be sure.

In my car, I took the stock antenna wire, added an antenna cable extension, cut off the end, and soldered it to a miniplug, which I then plugged into the RadioShark (the headphone input is supposed to double as an input). Now, I'm just getting static, so I figure that I may need to amplify the signal (this would make sense if the stock headunit had its own antenna preamp).

Am I thinking correctly or am I totally offbase? Anyone have any recommendations for a good amp that can do AM and FM frequencies?

Thanks very much!

**lez** · 11-09-2005, 03:18 AM

the aerial is just a metal stick.

Cut to an approximate size corresponding the a 1/4 or 3/8 of the 'wavelength' of the band its used on. bands are often call by the wavelength in the radio world, ie 70cm's is 450 mghz band, so you would 70*.25=18cm's etc

AM is just a fudge is the correct aerial length would be a little large on your car

And you can buy amped aerials, some cars have an amp included, some cars use the wires embedded in the rear screen (the heater) as the aerial and have an amp on that.

**Tzuknami** · 11-09-2005, 03:58 AM

[QUOTE=azzurro]
In my car, I took the stock antenna wire, added an antenna cable extension, cut off the end, and soldered it to a miniplug, which I then plugged into the RadioShark (the headphone input is supposed to double as an input). Now, I'm just getting static, so I figure that I may need to amplify the signal (this would make sense if the stock headunit had its own antenna preamp)./QUOTE]

I may be way off base here too but what type of mini plug did you use? Stereo or mono? If an output (headphones) doubles as an input (antenna in) then I'd be willing to bet that it would use a mono plug for the input. Unless of course it uses the ground pole of the headphone jack as an antenna anyway. Where on the mini plug (what terminals) did you solder the antenna to?

**azzurro** · 11-09-2005, 10:24 PM

Thanks very much for the responses!

Originally Posted by lez

the aerial is just a metal stick.

Cut to an approximate size corresponding the a 1/4 or 3/8 of the 'wavelength' of the band its used on. bands are often call by the wavelength in the radio world, ie 70cm's is 450 mghz band, so you would 70*.25=18cm's etc

AM is just a fudge is the correct aerial length would be a little large on your car

And you can buy amped aerials, some cars have an amp included, some cars use the wires embedded in the rear screen (the heater) as the aerial and have an amp on that.

Thank you for the information. Just so I'm perfectly clear, I can rephrase my question a different way: Car antennas have a standard connection at the end, so they still work with, for example, aftermarket head-units. Do these aftermarket head-units amplify the signal at all?

If the arial is just a metal stick, why are two wires needed?

Originally Posted by Tzuknami

I may be way off base here too but what type of mini plug did you use? Stereo or mono? If an output (headphones) doubles as an input (antenna in) then I'd be willing to bet that it would use a mono plug for the input. Unless of course it uses the ground pole of the headphone jack as an antenna anyway. Where on the mini plug (what terminals) did you solder the antenna to?

Great question. This may be the issue...

The car antenna wire is made up of two wires. The mini plug had two wires. Thus, two possible combinations. I tried both, to no avail.