CDM1550 Car Stereo Interference

ericsze · Post by **ericsze** » Fri Mar 21, 2003 9:23 pm

I just finished installing my CDM1550 in my SUV, rear mounted and the head unit was remoted to the center console. Everything seemed to be working well, little to no engine/alternator noise, etc. Then all of a sudden, I noticed that when I keyed up on the mic, the front passenger speaker (car stereo) would spit out static. Just like if you were to key up on a portable right in front of a computer speaker. This didn't happen right after I installed it and tested it out. It just came all of a sudden. The problem naturally disappears if you turn the car stereo off, but if anyone has any experience with this issue, it would be a great help.

Thanks.

Only the front passenger speaker makes the noise. No other speaker in the vehicle emits the noise.

elkbow · Post by **elkbow** » Fri Mar 21, 2003 9:40 pm

Where did you mount the antenna, what kind of SUV? Did you program some channels on low power and other on high power, assuming you have a 40 watt radio, and then try to see how much interferance you get on each power.

Where did you connect your ground wire? Is you power cable wired directly to the battery, are you running ignition control?

ericsze · Post by **ericsze** » Fri Mar 21, 2003 9:48 pm

1999 Mercedes Benz ML320, Antenna mag mounted just above the rear tailgate. Power runs directly to the battery, fused. Ground at chasis point, no ignition control. All channels are programmed on High Power, 45 watts.

During the first few days after the install, everything seemed to be working normally. I JUST noticed today after some use that when I key the mike, it causes the front passenger car stereo speaker to "spit some interference". It's only that speaker too.

Any ideas?

Equinox · Post by **Equinox** » Fri Mar 21, 2003 9:55 pm

Recheck your ground, as well as the SWR on the antenna.

fire-medic8104 · Post by **fire-medic8104** » Fri Mar 21, 2003 11:07 pm

you may also look for an external factory or aftermarket audio amp for the stereo. If the radio is mounted near one of these th rf will go into the speakers. I have seen this affect one or all of the speakers. You may shield it with aluminum or relocate it somewhere else in the vehicle.

perthcom · Post by **perthcom** » Sat Mar 22, 2003 3:59 pm

hi
All the wires in your vehicle act as antennas too. The strong RF signal coming off the 2way antenna induce a strong RF signal onto the speaker wires. The RF travels back into the radio and gets rectified by the audio power amplifier transistors. This rectified RF voltage puts the amplifier bias voltages all out of wack causing strange noises to be emitted from the speaker.
The amount of interference you experience depends on antenna placement, am/fm radio circuitry, where the speaker /coax wires run, VSWR, the moon, water tables and the menstraul cycles.. etc ... etc .... etc.
Get yourself some snap-on ferrite cores and put them on the speaker wires as close as possible to the am/fm radio itself. One or two on each wire should fix most or all of your problem.
The problem does not usually involve the power wiring as these have filtering for alternator noise etc which usually filters all the RF on them too.

jim · Post by **jim** » Sun Mar 23, 2003 8:17 am

fire-medic8104 wrote:you may also look for an external factory or aftermarket audio amp for the stereo. If the radio is mounted near one of these th rf will go into the speakers. I have seen this affect one or all of the speakers. You may shield it with aluminum or relocate it somewhere else in the vehicle.

Check VSWR first. These cars are famous for using composite materials and sometimes don't offer the necessary groud plane. If it is a ragtop, it may be affected even moreso.
If the radio is built properly, there will be no RF coming from it's case. Use a GOOD coax cable and not RG58- especially with a Motronic engine management system in that Daimler. I have seen some instanaces where the magnet mount antenna will require a separate #12 RF ground from the antenna to the chassis to eliminate RF/EMI. Try ferrites on the audio amp's power/ground and line-level inputs as well.

Also......most German autos use an amplified Fuba or similar antenna with EXTREMELY high gain in it's amplifer system. You mat be getting RF into the Fuba systems's B+ power. Ferrite beads will usually eliminate RF intrusion. If your trnsmit antenna's close to the radio antenna, you may never rid of this problem.