poor fm reception

[derek dj]

so i recently installed my subs in my new grand prix gxp and they are working great. but the fm frequencies that i used to get are horrible now. i only get 1 and it is very fuzzy where as it used to be clear. I am able to get am frequencies very clear and cds also play clear. I never touched my headunit as i used a line out converter so i couldnt have wiggled the antenna loose. I should also note that when i unplug the amp that the stations come back playing clear. Any ideas on what could be causing this guys?

[SlowNA06]

e.m.p. from power wire? Can't imagine that's the case, but I'm interested to see if anyone's got an answer.

[agentbluescreen]

On my 2000 GTP (and most all others) the rather crappy FM antenna is in/on the rear window's conductive defroster-tape system. For FM radio reception this "kludge" (no real external antenna) his means two things. First off the antenna is located inside the vehicle "behind" the window-glassware - this means that direct-to metal FM signals can only be captured when the windows are open and multipath (reflected and refracted) FM signals are all that the antenna can receive, since it is behind a solid glass RF-reflective surface inside the rear of the body's metal passenger-can. the second problem is that poorly filtered raw high frequency RF leakage from the voltage regulator and Ignition and Engine control computer strobes and output lines will overload the FM discriminator and RF-mixer's AGC (automatic gain control) circuitry of the FM tuner front end and demodulator circuits, especially when the rear window defroster is in use.

The rear window defroster acts as a rather dirty local RF noise (RFI) transmitter right next to (and actually part of) the antenna when it is powered on and so will anything else powered off of the poorly filtered car DC buss that is part of the rear (rear deck) window defogger-antenna contraption. Some sources have isolated this problem with the newly back in 2000 (year) patented device itself, indicating that any damaged heater tracks (ie: hot spots in the defroster) may actually be the reason the antenna function is badly degraded even more when the defroster is activated.

I have noticed no unusual hot spots in my defogger but in winter when ice and snow are on the glass the fault is very pronounced (possibly also during rainfall). In any event the antenna connection to the thing is in mid center of the back window top under the headliner, and a much (car wash resistant) better standard fixed antenna or power antenna can easily improve both fringe reception and FM multipath distortion problems on any radio. Unfortunately neither the premium Delco nor the Bose/Delphi radios have power antenna relay outputs having been designed only for this window antenna thingy.

The best solution is to install a genuine external FM radio antenna, there's really no way to get decent or better FM antenna performance in these cars without putting one in.

You will also notice that if you use a car lighter powered FM modulator (small transmitter) to hear your iPod, phone or Sirius radio with the radio it has to be high up on the dash since the weak antenna is way-off behind the back seat. A rear cigarette lighter socket or RV type 12VDC extension cord is needed in order to deal with that.