Antenna power weirdness - can anyone shed some light?
08-12-2007, 04:06 PM
#1
Rennlist Member
Thread Starter
Antenna power weirdness - can anyone shed some light?
I got my new stereo system installed (Alpine iPod headunit, 4 sets of speakers, front end amp + subwoofer amp) and as with the Alpine headunit that was in there before, the new radio has equally crappy FM reception. For example, an NPR station at 90.5 that my truck picks up perfectly on its bone-stock radio barely came in on the previous Alpine in the 928, and the new one is no better. Maybe it's Alpine, maybe it's the antenna.
I search these forums and find that it's fairly common for installers not to install the antenna power lead, so I figured I'd check it. I pull off the sunroof motor cover, find the antenna power wire, open the connector, and hook up my trusty multimeter to it. Everything checks out perfectly - power comes on only when the radio is turned on (and the source is set to a radio band, interestingly).
So here's the weird part - when I checked the antenna power, I noticed that the reception was a lot better with the antenna power DIS-connected. I checked both ways on stations across the dial - the lower-power public radio stations at the bottom of the dial all came in better with the antenna power disconnected. The higher-power stations across the rest of the dial were unaffected, though.
Isn't it totally NOT supposed to work this way? Anyone have an explanation?
(I checked my blinker fluid, so it's not that.)
I search these forums and find that it's fairly common for installers not to install the antenna power lead, so I figured I'd check it. I pull off the sunroof motor cover, find the antenna power wire, open the connector, and hook up my trusty multimeter to it. Everything checks out perfectly - power comes on only when the radio is turned on (and the source is set to a radio band, interestingly).
So here's the weird part - when I checked the antenna power, I noticed that the reception was a lot better with the antenna power DIS-connected. I checked both ways on stations across the dial - the lower-power public radio stations at the bottom of the dial all came in better with the antenna power disconnected. The higher-power stations across the rest of the dial were unaffected, though.
Isn't it totally NOT supposed to work this way? Anyone have an explanation?
(I checked my blinker fluid, so it's not that.)
08-20-2007, 12:23 PM
#3
My guess is that the amplifier in the antenna base is bad (assuming that you have the stock Fuba Betaflex antenna) or that there is an impedance mismatch between the antenna amplifier and the non-OEM radio(s). FWIW, I am not really inclined to believe that impedance mismatching would cause this, but I recall reading about this possibility somewhere more-or-less authoritative...
You did not mention AM reception: I understand that when the Fuba antenna amplifier fails, FM works but AM reception is lost. This, BTW, is an exact description of the problem with my '89 GT: no AM, FM seems fine with power to the antenna measured at the connector ot the antenna. The head unit is a Pioneer DEH P715.
I would suggest checking that the antenna base-mounting stud and nut are grounded to the chassis (disconnect signal and power cables first, and a PIA if the sun roof motor is not moved...). If that is good, you can further isolate the problem by temporarily connecting another antenna to the signal lead (DIN7?) in the sun roof area (or you can simply use a few feet of wire routed outside the car and held away from the car body: no amplifier needed).
If the substitute antenna gives good AM and FM reception, then the problem is the antenna, antenna amplifier (or that impedance thing....), if not, then there is a problem with the antenna cable or the radio itself.
FWIW, in trouble shooting my reception problem, a substitute antenna made no difference at first: FM worked, but no AM. A broken signal wire in the antenna cable from the radio at the connector in the center console caused this. Once that was fixed, the substitute antenna worked well when connected as described above. I also removed the antenna mast, reconnected the power and signal cables and connected the substitute antenna wire to the base outside the car to see if the mast was bad: it made no difference.
My conclusion was that the base was bad. I have one on order and it will hopefully arrive soon. I will devise Plan B if it does not solve my problem.
You could consider one of the shark fin antennas. I had thought about installing one, but decided that I did not really like how they looked. Also, with a newer receiver, you might find that you don't need an amplified antenna and that a passive one would be adequate (as suggested by the fact that your reception was better without power to the antenna's amplifier).
Good luck.
Bob
You did not mention AM reception: I understand that when the Fuba antenna amplifier fails, FM works but AM reception is lost. This, BTW, is an exact description of the problem with my '89 GT: no AM, FM seems fine with power to the antenna measured at the connector ot the antenna. The head unit is a Pioneer DEH P715.
I would suggest checking that the antenna base-mounting stud and nut are grounded to the chassis (disconnect signal and power cables first, and a PIA if the sun roof motor is not moved...). If that is good, you can further isolate the problem by temporarily connecting another antenna to the signal lead (DIN7?) in the sun roof area (or you can simply use a few feet of wire routed outside the car and held away from the car body: no amplifier needed).
If the substitute antenna gives good AM and FM reception, then the problem is the antenna, antenna amplifier (or that impedance thing....), if not, then there is a problem with the antenna cable or the radio itself.
FWIW, in trouble shooting my reception problem, a substitute antenna made no difference at first: FM worked, but no AM. A broken signal wire in the antenna cable from the radio at the connector in the center console caused this. Once that was fixed, the substitute antenna worked well when connected as described above. I also removed the antenna mast, reconnected the power and signal cables and connected the substitute antenna wire to the base outside the car to see if the mast was bad: it made no difference.
My conclusion was that the base was bad. I have one on order and it will hopefully arrive soon. I will devise Plan B if it does not solve my problem.
You could consider one of the shark fin antennas. I had thought about installing one, but decided that I did not really like how they looked. Also, with a newer receiver, you might find that you don't need an amplified antenna and that a passive one would be adequate (as suggested by the fact that your reception was better without power to the antenna's amplifier).
Good luck.
Bob
08-20-2007, 03:49 PM
#4
Rennlist Member
Thread Starter
Thanks for the info, Bob! I will check the AM reception and go from there. I assume the antenna wire from the headunit to the sunroof motor area is good if connecting/disconnecting the power lead affects the reception.
I was already considering changing to a shark fin antenna because I prefer the look, and because I cover the 928, so it would make that process a bit simpler. I might just go that route one way or another.
I was already considering changing to a shark fin antenna because I prefer the look, and because I cover the 928, so it would make that process a bit simpler. I might just go that route one way or another.
