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Car antenna repair

I am repairing my car's antenna wiring. Here's the background:

I purchased a new automatic antenna for my 1986 Lincoln Town Car & had it installed at the car stereo shop to replace the non-functional stock antenna since the car was new, the FM stations had some static and I couldn't receive any AM stations at all; the radio in my Town Car is an aftermarket Kenwood CD Head Unit. The radio is great and have no problems. I took this radio out of my previous vehicle (Toyota Camry) & reinstalled it in the Lincoln Town Car.

When the car is stopped, no engine running and on Accesory mode, I was able to barely hear AM broadcasts. However once the engine is running the AM band buzzes, has hissing & pops with a static barely, making it impossible to hear anything on the radio including local stations in the San Francisco Bay Area.

In the attached photo shows both wiring ends from the aftermarket antenna's cable to the car's existing antenna cable, cut off & was originally sealed with electrical tape. Could I use a coaxial cable splice connection, fuse them together using butt connectors, hard-wire the two ends (in the picture) or just purchase an antenna amplifier booster to fix the radio reception problem? I was also considering this, an inline AM/FM antenna noise filter for automobiles should fix the problem: ebay.com/itm/Car-Fm-Am-Radio-Stero-Inline-Antenna-Noise-Sound-Filter-/220807733152?pt=US_Wire_Harnesses&hash=item33692a9fa0

Another thing, the radio reception in my SUV's (Toyota Highlander) is suberb and no signal problems, as well.
car antenna connection.jpg
1788 x 1936 - 2M
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Comments

  • That antenna lead is hacked and hacked up badly. This antenna line is a shielded co-axial line that must maintain the integrity of the shield between the antenna and the car radio to have any chance of decent reception. The inner core, inside the white insulation, carries the antenna signal, while the braided copper shielding, negative ground, shields the inner core wire from electrical interference from all the other electrical noise inside the car. With the shield breached, noise can scramble the radio signals, giving bad reception. The cheapest fix is to properly splice the lines. The best fix is to run an unmolested line from the antenna to the radio, but would require a good bit of skill to do correctly if the antenna line at the antenna is built-in, not a quick connect.

    This discussion has some great ideas to properly splice the line: forums.corvetteforum.com/c4-general-discussion/1504486-can-you-splice-antenna-wire-like-regular-wire.html
  • Was that damage to the coaxial cable done by the car stereo shop? If so, they should fix this for you by using a proper type of splice, not a twist it and tape it splice. If they can't do it right, then they should go out of business, that is unacceptable workmanship.

    A coaxial line is an unbalanced line, meaning that if the shield has any holes in it, it becomes an antenna for any static in your area. That static filter won't help, don't waste your money.
  • It is never a good idea to splice coaxial cable. There are extension cables (I think I still have one) that plugs into the antenna cable and then connects to the radio. The signal to noise ration changes when you splice the cable and a booster will do nothing more than boost the noise.
    You may have to start over and replace the antenna.
  • By auto-antenna, I assume this is the kind that goes up and down by itself, when you turn the key to "on". I'm assuming you've verified the antenna is going up and down as it is supposed to. And that there is continuity on both the signal and shields from one end to the other. If so, then the splice is the problem.

    Connecting one piece of coax to another is usually done by putting a connector on each of the wires, then connecting the connectors together. I've done this inexpensively w/the rf connectors used for tv antennas, "F connectors" I think they call them. Radio Shack sells these, and this is fairly easy to do, if you're up to doing it yourself. You need one female, and one male type. Or two of the same type with a barrell adapter.

    F connectors are for 75 ohm cable. They should work fine for you as the run is fairly short, but there may be a different type of connector typically used for car antennas, as the cable may be 50 ohm instead. Maybe Google knows.

    Replacing the entire line with a new cable would work too.

  • edited October 2012
    Its not the signal to noise ratio that is affected by a splice, its the standing wave ratio. The quality of the splice can reduce the impact to almost zero if the right spice is used correctly. The issue is trying to keep the Characteristic Impedance (Zo) the same as the cable. I.e., use a 75Ω splice on a 75Ω cable. I good splice will usually require a heat gun.

    I agree the best solution would be to start over with a new antenna. I'm guessing that the antenna is on the rear fender and the so called tech didn't want to or didn't know how to snake the cable from the back of the car, so he just cut and spliced, very poorly at that.
  • edited October 2012
    The older radios like you have use what is called a Motorola Connector for the antenna connection. I believe they were the first or one of the first ones anyways to make radios for automobiles. You can get a splice connection using a plug and jack together. Here is a link for Radio Shack parts you need.

    http://www.radioshack.com/product/index.jsp?productId=2102835

    AM band radio waves are much longer in wavelength than FM band signals are so when a car antenna has problems the AM band is the first to detect a problem. Older radios usually had a tuning circuit for the antenna input. Most required you tune in a weak station for maximum signal at the upper end of the AM band to couple the antenna with the car body ground plane for best reception of the signal.
  • There is one more thing that is kind of critical for AM reception and that is the shield of the coax must connect to the ground plane at the base of the antenna mast. when you replace the antenna, you must clean around the underside of the hole in the fender right down to bare metal so that the base of the antenna makes good contact with the fender. If not done, AM just won't work.
  • edited October 2012
    Do I need to disconnect the battery in order to work on repairing the antenna cable? The antenna connector is located in the trunk. Once I repair the connectors, will my reception be greatly improved on both AM & FM? Also will the buzzing on AM stop & static diminishes on FM?
  • edited October 2012
    The antenna cable does not carry any voltage, but if you remove the antenna to make sure you have a good ground, then disconnecting the battery might be a good idea. If the repairs are done right, your reception should be greatly improved unless something is wrong with the radio.

    The ideal is to have an unbroken cable from the antenna to the receiver. Any splices or connectors along the way are going to degrade the signal. If you have to use them along the way, then use the best connectors or splices that you can get and follow instructions to the letter, this will minimize your losses.

    In most cases, the only losses you will notice will be on the fringe stations. Local stations are usually not affected by some small losses.
  • The factory wiring at the car's end was damaged & broken prior to purchasing the antenna. What the installer did was modified the connectors on the factory wiring & the new antenna by cutting both ends & wrapping it with electrical tape. I stand by their work & reputation.
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