Motorized antenna information & troubleshooting
 

(This began as an e-mail in response to questions from an SVX owner, but I decided to expand it a bit and post as a thread)

How motorized telescoping antennas work:

The car supplies a higher-current feed (from the battery), to run the antenna's motor. This receives power even without the ignition key, so that the antenna can finish retracting when you leave the car.

The antenna also receives a low-current control signal from the radio: +12V to raise the antenna, or 0V (or open circuit) to let the antenna retract. All Subaru factory radios that I'm aware of have a pin which can supply this signal. More recent Subaru car models have an antenna RF booster amplifier, which that pin on the radio will power directly.

In most cases, the radio only activates the antenna trigger signal when you're in AM or FM mode (and also Weather band, for models with that capability); off when in all other modes (tape, CD, aux, satellite radio, USB, etc.). However, some Subaru OEM radios leave the antenna trigger 'on' regardless of the audio source (i.e., the antenna won't retract when you switch to CD).

Most aftermarket radios have a 'power antenna' lead too. However, many only have a lead to trigger a speaker amp (which you can also use for the power antenna). In this case, the motorized antenna will be up the entire time the radio is on.

Inside the motorized antenna assembly, the trigger signal powers the coil of a relay which switches the higher current power to the antenna motor. Limit switches determine the polarity to the motor and cut the power when the antenna has fully extended or retracted.

In the SVX, the connector for the antenna motor has these three wires:

• Black = ground
• White = +12V constant (from fuse #22 in engine bay -- see attached diagram)
• Black/Green = control from radio

Troubleshooting:

When the motorized antenna stops working, these are the most likely reasons I can think of (besides mechanical damage):

A) The antenna motor is not getting its main power (due to blown fuse, bad or disconnected wiring, bad relay, or bad motor).

B) The antenna is not receiving the control signal from the radio (either due to bad wiring, or radio no longer providing the signal).

The easiest way to check all of that is at the power harness that plugs into the antenna, in the trunk. There you can use a voltmeter to verify that the harness has +12V on the appropriate pins. You can unplug that harness without needing to unbolt the antenna assembly itself.

If you find that the constant power is not there, check the fuse in the engine bay, and then the wiring between there and the antenna harness.

In the SVX, that same fuse powers some other circuits in the car, including the key warning switch (which is used by several systems, including the A/T shift lock system and automatic shoulder belt system), and the hazard switch. So if that fuse is blown, you should have noticed some other things stopped working too.

To test the car's antenna trigger wire, unplug the harness from the radio and connect a short jumper wire from the +12V battery pin to the power antenna pin. If all of the car's wiring is good, that should make the antenna extend. See pin-out table for the radio harness in my SVX Audio Install guide.

If the antenna motor works with your jumper wire but not with the radio, the radio's trigger output may be bad. Use a voltmeter to check that pin on the radio's socket. I've seen a case where a tiny surface-mount transistor inside the radio actually died (due to owner trying to draw too much current from the trigger lead), and it was possible to repair it. An easier alternative would be to power the antenna trigger from the car's +12V Accessory power (key-switched).


References:

If you haven't already, you should download the SVX wiring diagrams, which are available here (as well as a few other sites linked in various threads here).

See these other threads for related tips:

Clean or Replace Your Antenna Mast (has great pictures showing how to access the antenna's power harness)

Power Antenna Woes

Antenna motor?

Help me trouble shoot bad am/fm reception

Does the mast antenna ever go bad? Reception problems.

Rear glass antenna attachment wire ["Defroster wire" (sic)] (has picture of wire which attaches to secondary rear glass antenna)

Diagrams:

MB fuse panel (in engine bay):

Attachment 18504
http://www.subaru-svx.net/forum/atta...4&d=1432520527

FB fuse panel (in compartment):

Attachment 18505

Antenna parts (from parts.Subaru.com):

Attachment 18506