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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > AUDIO/VIDEO + BLUETOOTH + Electronics/Alarm/Software > Diversity Antenna Functionality



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      04-23-2013, 08:59 AM   #1
gte460z
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Diversity Antenna Functionality

I have been experiencing some a significant reduction in my FM radio signal quality lately when I used to have great reception. I have been looking into how the diversity system works on the e90 and came across this document: https://www.google.com/url?sa=t&rct=...45512109,d.dmQ

That document states that A) you can set the specific antenna to be used on the factory radio or keep it in diversity mode and B) the diversity antenna systems needs the factory radio because it receives a 10.7 MHz IF reference (on the antenna coax) from it to determine which antenna has the best quality.

Now my issue is that I have an aftermarket radio and the reception was fine until a week ago. I am thinking that at some point the diversity antenna decided it wanted to be on another antenna and switched (maybe due to a power cycle at some point, I'm always screwing around with stuff in the car) which resulted in my reduction of quality. If that is in fact the case, I will probably plug in my stock radio and set the antenna manually when I get home tonight to see if this rectifies the issue.

Is my understanding of how the diversity system works correct? Does installing an aftermarket radio really render the diversity antenna system useless? It seems silly to put the 10.7 MHz reference in the radio instead of just designing it into the diversity module...

**Edit** Now after looking at the diagram a little more, it seems that the diversity mode is controlled by the "Us" signal which is also on the antenna coax. That answers the question of whether the diversity systems works with an aftermarket radio and the answer is NO (unless you install a bias-pi, similar to a bias-t, to put 2.5V and 10.7 MHz on the antenna coax). It still does not explain why my radio reception mysteriously got worse over the past week. Maybe manually setting the antenna in radio service mode with the stock radio will still work.
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Last edited by gte460z; 04-23-2013 at 09:46 AM.
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      04-23-2013, 11:54 AM   #2
09E90utah
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Originally Posted by gte460z View Post
I have been experiencing some a significant reduction in my FM radio signal quality lately when I used to have great reception. I have been looking into how the diversity system works on the e90 and came across this document: https://www.google.com/url?sa=t&rct=...45512109,d.dmQ

That document states that A) you can set the specific antenna to be used on the factory radio or keep it in diversity mode and B) the diversity antenna systems needs the factory radio because it receives a 10.7 MHz IF reference (on the antenna coax) from it to determine which antenna has the best quality.

Now my issue is that I have an aftermarket radio and the reception was fine until a week ago. I am thinking that at some point the diversity antenna decided it wanted to be on another antenna and switched (maybe due to a power cycle at some point, I'm always screwing around with stuff in the car) which resulted in my reduction of quality. If that is in fact the case, I will probably plug in my stock radio and set the antenna manually when I get home tonight to see if this rectifies the issue.

Is my understanding of how the diversity system works correct? Does installing an aftermarket radio really render the diversity antenna system useless? It seems silly to put the 10.7 MHz reference in the radio instead of just designing it into the diversity module...

**Edit** Now after looking at the diagram a little more, it seems that the diversity mode is controlled by the "Us" signal which is also on the antenna coax. That answers the question of whether the diversity systems works with an aftermarket radio and the answer is NO (unless you install a bias-pi, similar to a bias-t, to put 2.5V and 10.7 MHz on the antenna coax). It still does not explain why my radio reception mysteriously got worse over the past week. Maybe manually setting the antenna in radio service mode with the stock radio will still work.
I am curious about the same thing. I have poor reception most of the time because of the diversity antenna. I have an aftermarket HU with digital radio. I was considering mounting an aftermarket antenna to bypass the stock unit.
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      04-23-2013, 02:58 PM   #3
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Well I will let you know. I plan on manually setting it to antenna 1 tonight via the radio service mode on the oem headunit.
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      04-28-2013, 10:20 PM   #4
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Sorry about taking so long to get back to this thread. I found that the setting does not stick for manually selecting the antenna with the OEM headunit and replacing it with the aftermarket. Oh well...
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      07-31-2013, 05:09 PM   #5
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I thought I would respond to this thread since I was experiencing the same issue with my aftermarket radio and tuner reception.

I'm not sure how you had the aftermarket radio hooked up, but I fixed my issue by connecting the my powered Metra antenna adapters 12volt wire to the aftermarkets blue wire (powered antenna) and to the Metras wiring harness' blue wire which lines up with pin 13 on the stock wiring harness.

I originally left these wires disconnected and wasn't getting any tuner reception at all. Once I hooked them up the radio was perfect.

Now, I also read the same diversity pdf and understand that the diversity antenna switches to find the best antenna. So I don't know how long before it does switch if ever. But for now I have clear tuner reception, we'll see how long it lasts!

I hope this helps if not you somebody else!
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