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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 08-09-2010, 12:33 PM   #1
pineypl
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Join Date: Apr 2009
Location: South Florida
Posts: 56
My Ride: 325ci
AM reception fix/DIY

Okay, many of us enjoy AM radio yet are not pleased with our car's reception. Mine was bad but proven horrific (if I may say that about mere radio reception) when I took my wife's Mini Cooper Clubman to work. I work 25 miles north of my home and also that much further from my favorite AM station which broadcasts from West Palm Beach, Florida. Well, I put on my station in the Clubbie and listened all the way to my office as if the station were near my office and not that I was traveling away from it. I could listen in the Clubbie so well I was thoroughly disappointed with the Bimmer. What to do? What to do? DIY or a mod of some sort!

The obvious differences in the cars are the antenna. The Bimmer's is in the window while the Clubbie's is a mast, albeit short, on the roof. So, to remedy that, I was not about to drill a hole to mount a mast and I was not able to locate the old style trunk mount antenna that does not require a hole. So I needed wire of some sort to make an antenna, but where do I put it?

As I was checking the location and double-checking my antenna amplifier connections, I noticed on my car, the rear window gasket is a groove-shaped affair. It looked as if I could simply lay some antenna wire in there and end up making a big loop around the rear window glass. My theory, as if I know anything about antennas and such, was to make a long antenna by making a loop, much like this.
Instructable AM antenna loop/
or like this


Off to Radio Shack to pick up a spool of 22 AWG antenna or hook up wire like this Radio Shack hook up wire. I picked that up for $6.99 + tax as I recall.

Disclaimer: In this project I removed interior covers, cut wires, soldered things, and modified electrical equipment in my BMW. You may do the same solely at your own risk. I cannot, nor will I be held accountable for you destroying your car, blowing it up, causing the FCC to fine you, burning down your home, ruining your interior, hurting yourself, killing yourself loved ones or animals, or getting run over in the parking lot at Radio Shack or your favorite electronics part store. This is merely presented as how I solved my problem of poor AM radio reception. Are we clear? PROCEED AT YOUR OWN RISK!

The project. I did not take any pics of the interior C-Pillar removal or such, there is plenty of that here in the forum. What I did was to remove the C-Pillar cover so I could get to the antenna amplifier connections. There is a long black sawtooth connection from the amplifier to the window antenna, item 6 in the image below. I needed to find which were radio and which were not. I found that the wires at connections #3 and #4 were what I needed. The black sawtooth connection is numbered, but they are very small, so just look and be patient to find them. How did I know? Well, I took the spool of wire and removed some insulation from the end and started poking it into the black sawtooth connection while it was disconnected from the window AND I had the radio on. Obviously if I did something right, a radio station would be heard. And that is exactly what happened.


I ran the wire back into the trunk and across to the passenger side where there is a rubber grommeted opening for the wiring to the trunk lid. Here is where my antenna came into the car.


According to what I could find about antennas, I needed to make at least 2 turns in one inch where I wanted the loop to end. I think they call it a choke. Anyway, you can see some twists there to do just that.

I ran the wire around the window in the recess of the gasket around the glass. The bottom of the window does not have that gasket, but it does have a groove where the adhesive is between the body and the glass. I simply ran the wire there and it all sits well. I did pull it snug and twisted it tight so as not to have it come loose while driving. I am going to use some black adhesive caulk at the top of the window to hold the wire, as the top of the glass actually is concave down, so the wire is fully exposed and I think I want it secured from wind. This image is taken from the passenger side looking toward the driver side and the camera was rotated 90 degrees. My fingernail is touching the black antenna wire.


Finally I made sure my twists were good and then I made a "drip loop" before I ran the wires in through the grommet. Both ends went across the trunk and into the C-Pillar on the driver side and connected to the #3 and #4 wires going into the antenna amplifier. I cut the leads that ran from #3 and #4 at the black sawtooth piece going into the antenna amplifier. Sorry I did not take a pic of this, I was trying to beat the rain. What you want is to bypass the glass antenna and only use the new one.


AM Results: I am now able to travel 22 miles north before I lose signal from my favorite AM station. To me, the $7 or so and an hour of my time were well worth it to gain an additional 22 miles of listening time for my station. Previously I would lose the station about 2 miles north of my home.

FM Results: Once at my office, Palm City Florida in case anyone cares, I let the radio scan for FM stations. Was I surprised, I used to get about 4 or 5 stations up here to stop the scan. Now I get over 12! The antenna project is a resounding success.

I have a friend who is a HAM and he will help me tweak the antenna. I may put a different choke on it and perhaps a variable capacitor to allow me to fine tune the antenna a bit.

Of course ask away if you have any questions, I'll do my best to answer them. And no, I did not lose any reception for my remote locking feature. Ultimately this is a pretty stealth solution and no real damage was done to the car other than cutting two wires. FWIW, the wire harness I cut only costs $12.00 USD according to RealOEM.com to replace, so it is not a huge deal to restore this mod to factory spec.
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Old 10-07-2010, 11:34 AM   #2
Xalky
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Location: Connecticut
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This is exactly what I need for my car. I get absolutely no stations on AM.

People say "who listens to AM?". I do... Traffic and weather are updated every 10 minutes on some stations in my area. And theres also some real good talk radio on AM. I get sick of listening to the same old tunes on FM. I also have Sirius and an Ipod connected via a Dice unit in my car but sometimes I just wanna know the traffic report and listen to some syndicated or local AM talk. Is that too much to ask.

I'm gonna give this DIY a shot today.

I have most of the rear trim off it anyway. Changed shocks. Just doing my TLC bit today.
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Old 10-07-2010, 04:32 PM   #3
Xalky
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This didn't work for me. Looking for a better solution to the reception problem.

Edit: i fixed the AM reception problem on my E46. I started with this great link I found: http://www.bimmerfest.com/forums/sho....php?p=4494437

A great tip is to do all your antenna tinkering with the AM radio on and tuned in to a station thats barely audible. Thats how I came upon the happy accident below.

In my case it turned out to be in the rear amplifier thats in the C pillar. I started by tightening the antenna lead with a pair of long nose pliers, it worked a little so I tred tighning it a little more and the long nose scratched thru the paint on the body, and lo and behold, the radio was coming in nice and clear. So it was a grounding issue to the amplifier. So I proceeded to try and remove the torx screws but they're in an awkward position. The easiest screw to get at is closest to the door. I proceeded to unscrew that and the station momentarily came in clearer. So then I went ahead and tightened it back down tight and now it works great.

Is it as good as the AM reception in my Express Van with an antenna mast...no... but its way better than it ever was. Befor I only got one station, thats in the next town over. Now I get probably about 10 stations. Even a couple of NYC stations which is about 70 miles away from my house.

I'm satisfied.

Last edited by Xalky; 10-08-2010 at 05:59 PM.
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Old 01-18-2011, 11:40 AM   #4
jbielefeld
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Inadequate AM radio reception

I also suffer from bad AM Radio Reception. But being a ham radio guy I had to get to the bottom of the problem:
1. I noticed that I got a lot of background static on week stations.
2. AM reception on my other vehicles (Pilot, Accord, and RAV-4 had great reception particularly talk radio 1200 here in Littleton, MA. On the Beemer I cannot receive this station.

Here is what I did:
1. Establish the receiver noise. Disconnected the antenna lead behind the radio. I got a soft hiss. This is the receiver noise floor. The alpine radio (stock BMW radio) seems to have a normal noise level. I then added a 5 foot wire to the antenna connector on the back of the radio. The back ground atmospheric noise was much louder than the radio noise. That means the radio has ample sensitivity that is the atmospheric noise is louder than the radio noise. That is good so far.
2. Is the cable from the radio to the antenna amplifier in good order. I reattached the cable to the back of the radio. then I detached the antenna cable at the antenna amplifier. I noticed the noise from the radio dropped to the soft hiss which is the radio receiver noise. So the cable is fine. I replaced the antenna cable on the antenna amplifier. I then disconnected the connector from the rear window antenna and the antenna amplifier. The background noise dropped very little. But was still much louder than the just the receiver noise. This means the antenna amplifier adds some noise to the system. It adds enough noise the override the receiver noise. So the antenna amplifier establishes the overall noise floor of the system. When I reattached the antenna cable to the antenna amplifier the atmospheric noise from the antenna did not override the system noise. That means the antenna on the rear window does not detect enough energy to override the receiver system noise. Bummer....
I removed the connector at the rear window and added a 5 foot wire to pin 4 and the reception was better than that from the window antenna. I then ran the wire outside of the car through the driver rear door. The reception went way up! Same performance as my other cars. I then moved the 5 foot wire to the rear window in the same location as the built in AM antenna location and the reception was poor but better than the original antenna.
So I conclude:
1. The car metal shell acts as a shield attenuating the reception.
2. The rear window antenna is way inadequate for the task.
With both of these problems combined reception will only be possible with close in AM stations.
Solutions:
1. Add an external antenna as most of the cars have.
2. Live with it...
3. Use the current antenna with a low noise pre-amplifier between the antenna and the antenna amplifier that will boost the antenna reception above the system noise. Humm...
I am working on option 3:
I designed and built a low noise FET (field effect transistor) pre-amplifier that has a 10x amplification. FET transistors will only add 3db to 4db of noise with a gain of 20db. I cut the wires between the antenna connector and the antenna amplifier connector and soldered the pre-amplifier between the two.
The pre-amplifier for the time being runs on a 9 volt battery until it can prove its self.
One thing I also did was add a 0.1uf capacitor from the top defroster connection on the window edge to pin 4 on the antenna connector. The AM reception improved remarkably! I use a capacitor to block the 12v when the defroster is turned on to prevent DC voltage from frying the antenna amplifier.
Then I added the pre-amplifier and reception is very good.
I can now hear Win10-10 news from NY! in Massachusetts.
Checked the following:
1. Keyless entry still works.
2. Defroster still works (does add noise to the reception when on).

So for now I will test this set up and if I like it I will then dress up the wiring so it all fits in the C-column. I will not publish the schematic of the pre-amplifier until I have it finalized.

Some theory:
Every receiver generates its own noise. To listen to a station you need a signal that is 6 to 7 times stronger than the receiver system noise for comfortable listening (IE: 10db S/N ratio). This is the job of the antenna. The E46 antenna is inadequate. Remember that nature also produces its own noise. As such the pre-amplifier will amplify both the atmospheric noise and the signal noise plus its own noise. In order to receive any signals the signal must be greater than all the combined noises by a factor of 6 to 7 times.
What if I were to add a pre-amplifier with a ton of gain? Here is the problem with that. The receiver has designed in an automatic gain control (AGC) circuit to increase the gain on weak stations and to reduce the gain on strong stations. This maintains a constant volume at the speakers. Since any pre-amplifier is a broad band amplifier the strong stations will be amplified along with the weak stations. The radio circuitry separates the stations as you tune the dial. If a strong station is amplified beyond a certain point the receiver will get overloaded and will not be able to filter out that very strong station (do to blow-by) as such it will trigger the AGC circuit to reduce its gain and you will not be hearing any weaker stations. In fact you will only hear one station all over the dial. The strong station has blocked the receiver (i.e.: receiver blocking or fundamental overload). So adjust your pre-amplifier gain so that the natural atmospheric noise received by the antenna slightly overrides the radio system noise but no further than that. Any station weaker than the atmospheric noise is too weak to be received no matter what you do.

Let me know if this helps.



John
2003 325i
K1JEB
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Old 01-18-2011, 02:45 PM   #5
mikeyb74
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Mine suffers from poor FM reception.
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The BMW e46 3er Sport Wagen...

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swell to lure folks out of those cumbersome utes." -Car and Driver

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Old 01-18-2011, 06:21 PM   #6
jbielefeld
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Mike,
Same priciple. Remove the antenna behind the radio. Put a wire 5 feet long on the radio conector and see if you get any FM stations. If:
1. you recive a signals radio OK.
2. you do not get any signals the radio needs repair.

If radio OK then reconect the radio antenna cable. Go to the antenna amplifier and remove the coax cable to the radio. Attach the 5 foot wire to the cable center conductor. If:
1. you get a signal cable is OK
2. you do not get a signal cable problem...

If you get a signal then reconect the cable to the radio to the antenna amplifier. Then unscrew and rescrew the torx screws conecting the antenna amplifier to the car metal. If:
1. you get a signal the grounding is fixed.
2. you do not get a signal then keep going...

If you do not get a signal then remove the conector between the antenna amplifier and the rear window (the window side conector that is). Caution this conector breaks easily! Touch the 5 foot wire to each terminal on the conector and see if you get a signal. If:
1. you do get a signal the FM part of the rear window antenna element is damaged.
2. you do not get a signal check that there is 12v going to the antenna amplifier (blue wire i think) but then if there is no 12 v then you should not have any keyless entry or AM radio. So that leaves you with a defective antenna amplifier.

Now I have not done this on a BMW but have done it on other cars this way... for FM trouble shooting that is.

Just find where the signal stops by deviding and concering one section at a time.
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Old 07-15-2013, 01:30 PM   #7
Assimilator1
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One thing I also did was add a 0.1uf capacitor from the top defroster connection on the window edge to pin 4 on the antenna connector. The AM reception improved remarkably! I use a capacitor to block the 12v when the defroster is turned on to prevent DC voltage from frying the antenna amplifier.

Re the 0.1uf cap & the top defroster connection on the window edge, do you mean on the plug or directly onto the vertical line?

Re blocking the 12v to the ant amp RF input, don't you mean a diode?

Btw thx for your in depth diagnostics

Last edited by Assimilator1; 07-15-2013 at 02:06 PM.
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Old 07-16-2013, 04:47 PM   #8
kd7iwp
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Quote:
Originally Posted by Assimilator1 View Post
[I]Re the 0.1uf cap & the top defroster connection on the window edge, do you mean on the plug or directly onto the vertical line?
I was wondering about this as well. Seems like a diode is desired to block the flow of current coming from the defroster. I didn't think a capacitor would provide that feature.
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Old 07-17-2013, 02:51 PM   #9
Assimilator1
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No you're right, AFAIK capacitors are mainly used for smoothing out voltage, but I'm no electronic engineer .

I had a fiddle with ant amp etc today, the coax was slightly loose but not enough to cause a problem, tweaking the earth screws helped a bit. Removing the black ant plugs & spraying them with contact cleaner didn't seem to help.
Btw I noticed if I disconnected the blue wire (earth for the heated screen) the back ground hiss reduced substantially, what's the cause of this?
Oh & AM reception suffers massive interference from the heated screen, & FM to a lesser degree too.

Last edited by Assimilator1; 07-20-2013 at 08:51 AM.
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Old 07-19-2013, 09:53 PM   #10
kd7iwp
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AM reception fix/DIY

Yesterday I took a look at my 2001 325i to see why I get no AM at all. The grounding screws on the antenna amp are fine, it's when I connected a piece of wire to pin 4 of the connector that goes onto the window that I got reception. I was required to hang that wire outside of the door though. When I draped the wire over the parcel shelf behind the rear headrests I no longer got reception. So I'm not sure if the wires on the window are bad or if it's simply a bad location on the car for an antenna.

The next thing I will try is putting my ohm meter on various parts of the antenna traces on the window to see if there are any breaks. Perhaps this won't work though if there is Amy type of coating on the wire traces. I say this because I tried touching my spare piece of wire to the traces on the window while holding the end of the wire outside of the car and that did not affect reception.


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Old 07-20-2013, 09:04 AM   #11
Assimilator1
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I think the lines do have a thin coating, or the surface oxidises, anyway you can make contact with meter probes, you might need to very lightly twist them though to make contact.

I tried on my car to give the blue wire a separate earth, it didn't seem to make much difference to the background hiss though. All the lines looked ok, not even any slight blemishes (I've got good eyesight btw).

I do have some AM reception, but I'm going to try a wire on pin 4 to see if that improves it.
FM reception is fine, except when the rear heated window is on.

Just been reading the BMW WDS and found this :-

Wave trap / radio reception
Radio reception

Wave traps are required on the supply lines for the purpose of using the conductors of the rear window defogger for radio reception purposes. The wave trap of the positive supply consists of a positive input and two outputs for the two heating sections of the rear window. A wave trap is also connected to each of the connections of the two heating sections to ground.

Wave trap

The wave traps prevent the high frequency active aerial currents flowing via the positive or ground terminal. The wave traps also reduce conducted interference from the rear window supply.


So maybe one the wave traps on mine is faulty? But how do I test them? I'm not even sure what they are, chokes??

[update]
Just found this thread with some useful info about the 'main' wave trap on the RHS http://forum.e46fanatics.com/showthread.php?t=818519
I'm going to check the power solder joints on the Wave trap 1 next chance I get.

Last edited by Assimilator1; 07-20-2013 at 10:02 AM.
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