This will be very general but will help you get the idea. Antenna theory is that the best reception will be provided by an antenna that is one wave length long. There is a formula to calculate this length which I have long forgotton, but lets say that the wave length for the center of the FM bands is 50 feet. The best antenna would then be 50 feet long, not to practical for a car. The next best is 1/2 wave length, then 1/4 and so on. Another way to electrically extend an antenna's length and get antenna's to work pretty well is to add a mathcing transformer to the antenna to make it appear electrically longer than the 30 inch solid steel mast that is on many cars. The wire (wound around the mast you are using) is the antenna in your situation and is electrically much longer than the solid steel mast you took off and probably, just by luck, comes closer to being a more beneficial length for your application. It could, just as easily, have been worse, but if it works, go for it. :D

 

I was was actually told it was for wind noise reduction and since it is mounted on the rear of the C5 it is not needed. I might have to switch with my Tahoe and see if it more technical than this alleged noise....

 

why does GM put that ugly antenna on a vette in the first place...they can put internal antenna's in the car and it will work fine right through the fiberglass body :yesnod: and like the coupe rear 1/4 pannel will look better :cheers:

 

As a Coupe owner I can attest to the poor radio reception. I was thinking about mounting a fixed mast antenna hidden somewhere on the car to see if I can improve on it. The area I live in is right in the middle between LA and
San Diego. Real bad reception. Mike

 

Finally, something I know a tiny bit about! :cool:

The formula for calculating the wavelength of an FM broadcast (or any electromagnetic signal for that matter) is:

c = frequency * wavelength

c is the speed of light, and it is 3x10^8 meters/second.
frequency of the middle of the FM band is around 100 MHz.

Plugging this in gives:

wavelength = 3*10^8/100*10^6 = 3 meters.

That said, obviously a 3 meter antenna would be rather long. A 1.5 meter or .75 meter antenna would be sufficient for most users. This is assuming that you have the physical setup to correctly pull the signal in. What I mean is, you have to have a proper electrical circuit. The major problem with a fiberglass body car is that there is not a proper groundplane of sufficient capacity to "sink" the signal.

I have heard of people using a wire mesh in their trunk (the bigger the better), connected to the metal ground post of the antenna. This would simulate how an antenna would connect to a metal-body car.

A good FM antenna (like on the top of somebody's house) has numerous "pickups" or "elements" that are tuned to specific wavelengths. They cover the entire FM spectrum efficiently and can pull in very weak signals.

Another important thing to consider about antennas is that their electrical impedance must match that of a vacuum (around 300 ohms, and the impedance of air is very close to that of a vacuum). This where antenna design quickly enters the realm of electrical engineering and lots of fun calculus. Suffice it to say that you can build a nifty FM antenna using 300 ohm twin-lead antenna wire (that brown, flat stuff). All you need is something that looks like this:

. . <-------------- approx. 1.5 meters -------->
. . ___________________________________
. . ________________ .__________________
. . . . . . . . . . . . . . . . | |
. . . . . . . . . . . . . . . . | |
. . . . . . . . . . . . . . . . | |
. . . . . . . . . . . . . . . . | |
. . . . (ant. pickup) <--O O--||| (ground)

<edit> After I posted this I realized that my little picture didn't look right. Sorry, but the vertical lines are supposed to be centered in the 1.5 meter section. I have tried to fix this, hope it looks better. Ignore the little dots - they are spacers to help the picture out. Note that the top horizontal wire isn't connected to anything - but it helps make the bottom horizontal wire "see" 300 ohms. Ain't physics grand?

Note that (ant. pickup) is the antenna connection on your receiver. There are two connections on the back of your receiver, and one is simply connected to ground internally. This is connected to ground at your house, or the biggest piece of metal inside the radio if it's a portable (but let's not confuse the issue here...) Also note that the length of the wire coming down doesn't really matter as long is it is vertically oriented. The 1.5 meter section should be horizontally oriented.

I made one of these when I was in college so I could pick up our tiny school station inside my dorm room. It was tuned for 89.7 MHz, if I remember correctly.

So, if you really want to find out how good your reception in your Z can be, get a piece of wire mess (the finer the better) approximately 3 feet by 2 feet in size, and connect a wire from the ground post on your antenna to it. Carry it around in your trunk for a few days, and if you like it you could cover it with a piece of cloth or something. But would anybody really do this?



[Modified by Cybercowboy, 12:01 PM 2/10/2002]

 

WOW.... hope your getting paid to know stuff like that :eek: :eek: :eek:

 

Also, the windshield antenna of my coupe seems to work great for FM, but is very marginal for AM (like for NASCAR - MRN). The Z06 has a much thinner windshield, and is most likely the reason they don't hide the antenna in there. Additionally, since the Z06's design goal was/is ultra light weight, they didn't put in a motorized antenna --- too much weight for the motor apparatus.




[Modified by EscapePod, 1:46 AM 2/11/2002]

 

Cybercowboy. First time I saw this version. Usually people tie the top and bottom ends together to create a folded dipole. Guess both versions work ok.

 

It's been awhile so I'm a little fuzzy exactly why but the version I posted was indeed what I used. I have seen the versions you are talking about (the kind you can buy) but at the time I first tried this I was taking an EE class called "Fields and Waves". This design was in the textbook and I think they were making the point that the induced signal did not depend on the completed conductive circuit, but rather the impedance match being the major contributor. But that was about 18 years and a different career ago...

 

Me too - even more than 18 years. I believe the advantage of the folded dipole is length - your 1/2 wavelength 1.5m becomes a full wavelength with slightly better performance. :seeya

 

Now I remember! When I was in college I was so broke that I couldn't afford to twist the ends together... ;) :smash:

 

Now I remember! When I was in college I was so broke that I couldn't afford to twist the ends together... ;) =====:smash:

(sorry 'bout the double post - the server is apparently having some issues...)


[Modified by Cybercowboy, 12:21 PM 2/11/2002]