ugabulldog

I plan on doing Bob98sr5's tech write-up on switching from my electric antenna to the tacoma whip, I live in SC and want to pick up the ga football games on AM radio, so I'm wondering if there's a better antenna to use, and also will that particular antenna works in place of the taco whip just as easy??

mike_d

chances are that it won't matter what antenna you pick. the antenna is only for FM reception. AM radio frequencies are much smaller than FM frequencies that they require an antenna that's much much longer. The AM antenna is just a coil of wire probably in the radio itself. to tune AM, the length of the antenna is adjusted so that it works for the correct frequency.

A little physics for those who care: First there are alot of different kinds of antennas you can get, but a common one is one that's 1/4 the wavelength of what you're trying to receive.

FM is generally considered 88MHz-108MHz so the wavelength is between 2.7m-3.4m. so they usually split the difference and say that the average wavelenth is about 3m. so if we want an antenna that's 1/4 the wavelength, that's .75m or about 30 inches. ever notice that you get better reception around 98.1 than you do at either end of the FM range? that's because the antenna works best there.

AM is 540kHz-1600kHz so the wavelenght is between 190m-560m. notice that the range is much much bigger than FM? so here, you can't easily have an antenna that's almost right for the whole range. so what they do is have a big antenna (probably 1/4 wavelength, but i'm not sure) that's about 150m long in a big coil. then by adjusting the distance electrodes are spearated on the coil they can pick how long the effective antenna is and tune the frequency that way.

So my guess is that the AM never uses any part of the FM antenna because it tunes a different way. or if it does use the FM antenna, any changes you make are going to be on a much smaller scale than the 150m internal coiled antenna inside the radio.

I'm sure there's HAM radio operator on the board that knows much more about antenna theory than i do, maybe they can chime in with more information and correct any mistakes that i made.

ldivinag

nice job mike.

1 tip, if you like a station in the either side of 98.1, you can cut (or extend, but this is maybe harder...lol....) your antenna (using mike's formula and "tune" it that way...)



you are better off in rotating the head unit to tune the AM stations... but then again, that's close to impossible in a car...