Another antenna question for the electronics guys.....

[Big Dan]

The cb has long been gone from my Ultra, but I still run 2 shorty antennas for the symmetry. Would it be possible, or even worthwhile, to split the fm antenna cable and use both shorties for the radio? Would the extra "length" of the second antenna actually do anything, or is the length question more a matter of height?

[MMOCGuy]

The theory is a bit more complicated that I'm laying out here but, hopefully this will answer your question without getting too technical.

The most efficient antenna is one that is the correct length for the radio frequency. I believe that the normal auto FM antenna is about 57" (I'm not near one to measure it) which is a compromise between optimum length and asthetics. With that said, you will get some reception even with an antenna that is not the optimum length. When using an antenna that is not the optimum length, the signal strength is decreased in a ratio related to how far off the correct length the antenna is. When you use dual antennae joined into one cable, what happens is that you increase what strength of incoming signal there is at the antenna. What you are proposing should work. The question will be how far from the radio station tower will you get a decent signal that isn't fuzzy or breaking up on you. You can only find that out by trying it.

Hope this helps.

Norm.

[Scramjet]

Normal auto antennas are 31".  I believe anything you do to alter the stock antenna, including your splitting scheme, will diminish the reception.

B

[Glenn W]

As I recall, the avg FM wavelength is 59". That's a little unwieldy so most car antennas are half wave or 29½". Halve that again for a ¼ wave and you'll get the 14"-15" length of most shorties. Running two parallel antenas will sometimes improve the strength of the input signal to the radio, depends on how strong the signal is in the first place. You'll need to use shielded cable & Y splitter so that the run from the second antenna doesn't become some goofy length antenna in it's own right. Never played with the OEM antennas so I don't know if they are grounded to the chassis. If not, you'll want to avoid having your splitter or connectors grounding to the frame or you can create a ground loop with the radio head unit's ground as the other end. That'll pick up noise & other garbage.

[Big Dan]

I ended up running the 2 antennae in series, and it works great. I could only get 2 radio stations before (way out here in the sticks), and now I'm getting stations from Milwaukee, Madison, Chicago, and I don't know where all else. The only thing you have to be careful of is that the outer shell of the fm coax is the ground for the stereo system. You want to connect the inner to the second antenna, while isolating it from the outer. A strategically placed nylon washer did the trick. The wire that connects the two runs inside the tailight housing, between the name plate and the outer wall of the tourpak.