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Old 08-07-2010, 02:52 AM   #56 (permalink)
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Long winded reply follows, you have been warned.

Comptiger is right, it is not that critical for receiving, however...

The most efficient length of an antenna is (in meters)
L=Length in Meters
F=Frequency in Mhz
You can substitute 3/4 for 1/4 but that will give you a longer antenna.

So your standard FM antenna is 1/4*300/100=0.75 meters. with a range of 0.84 meters to 0.69 meters. (Not worth adjusting for, you will have other errors not accounted for here.)

AM is considerably longer: 1/4*300/1 = 75 Meters. (AM antennas are usually coils of wire, not a straight stick.)

If you are in a metropolitan area, window mounted antenna work fine, sometimes even better than external. (due to your signal being overpowered by other stations.)

a close proximity to a parallel piece of metal will degrade the performance of any antenna. They work best with an ground plane at the bottom (or top) for this type of antenna. (You can use a reflector if you work it out right but it is very directional.)

If you remove the other connections to the defogger wire, Yes, it can make a decent antenna. If you don't unhook the voltage and ground, you can either fry your radio or it could be useless because it is grounded. (you could use other parts to make this work and have a defogger that works, but that is beyond the scope of this reply.)

You can use 30ga magnet wire to recieve, the size is for structural integrity.

I remember my dad getting a kit for a windshield antenna. Some scotch tape and magnet wire will do.

Build the antenna right, and you don't have to switch around.

One last thing, a vertical wire is better than an horizontal wire for a mobile application.

In conclusion, take a coax cable from the radio to a point in the middle of your windshield, solder some 30 gauge magnet wire to it, and tape it up the middle of your windshield stopping about 2 inches from the top. Use good tape (3m "Magic" will work well.) and you have an invisible antenna.

Originally Posted by Otto View Post
OK, since some of you guys are knowledgeable on antenna stuff and I'm not, could we review a few things and answer a few questions?

1. Antenna length is a function of radio wave length...

2. If correct, that suggests an adjustable or telescoping antenna would be most versatile and receptive...

3. Inside the car reception is nearly as good as outside...

4. An antenna stuck in the weather strip between door and roof ...

5. You can hook up your antenna circuit to your rear window defroster ...

6. The type and thickness of antenna wire or pole is irrelevant,...

7. Some windshields have antennas inside the glass, ...

8. Why not do the same at the back window, ...

I know squat about this stuff, so please chime in with suggestions for improvement.
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