dmberendsen

I've installed an Alpine radio and hid the 12v powered antenna behind the top of the back seat. The quality of reception comes and goes but when its not good it instantly gets much better if I touch the antenna ground. I think I've seen this before but cannot remember why this happens. Do I become a better antenna? I grounded it at the same ground as the conv. top motor and am sure its good and clean. Do I need to get a blow up girlfriend, belt her in the backseat and make her hold it? I'd appreciate a better solution or at least an idea of what's happening.


Thanks in advance.

Yellowstatue

If you are on the AM band you must adjust the 'antenna trimmer' on a given antenna length, and on FM the antenna should be thirty-one inches long.

Rocketowner

Amazon has antennae signal booster /amplifier made for automotive and Boat radio reception. It is usually a problem with the antennae mounted inside the vehicle. Larry

dmberendsen

I'll look into this. Thanks, Yellowstatue.

oldcutlass

Antenna's generally don't work very well (especially for AM) hidden under cover blocked by body panels. Why not just install a fender mount.

redoldsman

If it sounded good with the ground why don't you just leave the ground on it? The cable is a coaxial cable and the shield needs to be grounded to be effective.

cjsdad

Obviously you would get the best reception with the antenna in a vertical position sticking up above the body panels. You will have greatly diminished reception with the antenna laying horizontal and below the RF-blocking metal of the car body. With the antenna sticking up above the ground plane of the vehicle you capture the most electrical energy. Where I live, I drive through a canyon to get into Albuquerque proper and as I leave the canyon, FM reception improves almost instantly. The antenna is designed to be mounted on a surface that isolates the mast above the ground plane of the sheet metal so even though your antenna base is grounded, it is not creating the necessary isolation for the mast. The human body does capture RF energy that passes into the antenna as you touch it so that may explain the difference. I was a professional stereo installer for 15 years and saw an extremely high number of antenna coax extensions that were bad out of the box (package). You might try another one or plug the antenna directly into the head unit and lay it on the floor. If reception improves, you have a bad one.

Rocketowner

If the look of a regular antennae is your objection to mounting it outside,you might consider a good power Antannae. The mast would only be visible when using the radio and reception would certainly be improved. Just a thought. Carid has one listed for around $80. Larry

dmberendsen

My goal was simply to clean up the outside of the car for appearance and ease of putting a cover on. I had a couple amplified antennas around that appear to be unused so what the heck. I seems odd to me after doing some of the suggested tests you guys kindly offered I found the amplified antennas worked worse (even when held in the air) than a cheap mast antenna. I guess there simply is no substitute. After all, I already have the antenna hole in the fender so the mast it will be.


Thanks again for your inputs.

oldcutlass

The amplified antennas will amplify noise in addition to the broadcast signal.

cjsdad

Sorry, I misunderstood the "12v powered antenna" part in your first post. The amplified antennas absolutely need a ground plane to work correctly. They are usually smaller/shorter and as mentioned above, an FM antenna needs to be 31 inches long for maximum reception so they are amplified to simulate a full size antenna. That is why it works better when you touch it, you become the RF ground it needs.

Also mentioned above, a power antenna is an option that hides well when not in use. There are also manual antennas that collapse below the surface of the fender and are quite nice.

Fun71

I agree with everything cjsdad posted - it is exactly what my communications professor in college told us.

dmberendsen

Thanks again for the additional info. My only other question is the antennae available are usually longer or shorter than 31 inches. Is that a problem? Can that be adjusted during installation?

Yellowstatue

Usually a one piece antenna is thirty-one inches, and the other antennae with multiple sections are of course adjustable. If you mostly listen to AM and live in the woods then you would have the antenna at full length, and if you live near town, then you could have your antenna much shorter. However, when you figure out what length you like then adjust the trimer for peak performance.

cjsdad

Yeah, the one piece antennas are optimized for the FM band. It's a rock-n-roll thing. The popularity of FM stereo created a demand for the always correct length antenna. Power antennas are also typically 31 inches when extended. There are two types of manually adjustable antennas and you guessed it. Some are only 31 inches and optimized for FM and some can be longer to improve AM reception. The fully collapsible manual antennas are typically 31 inches but can obviously be shorter if you don't pull them all the way up. If you are after maximum AM reception you will need the above-the-fender extendable type.

dmberendsen

Thanks guys. Having the correct info always makes the decisions easy.