replacing a glass mounted grid antenna with a whip mounted on the hatch

nlinesk8s

New Member
Apologies if I'm in the wrong place, but my typical automotive sources really don't know about this, but I think it should be fairly basic. So tell me why I can't do this.

I've a 2003 Mercedes c230 hatchback. The radio/IR key fob antenna is mounted against a grid on the glass.

Three big problems:
1) if you open the hatch and add tinting, which people tend to do on hatchbacks, water runs down the glass and shorts out the amp, which is mounted at the top of the hatchback glass nearest the hinge.
2) They put the amp between the glass and the metal surround of the hatch, so to do a good install, you have to remove the glass, driving the install cost through the stratosphere.
3) The replacements cost between $500-$600. That's just the part. For a friggin antenna amp.

Paying someone (Mercedes) big money for a bad design sort of offends me. I was hoping for a better solution, but the level of technical capability on the MB forums is such that "go to the dealer" is their default answer to everything (or confused silence)

So, what I was wondering was whether I could buy an amplified whip antenna, drill a hole through the hatch glass, and connect to the existing wiring. As I've a grid on the glass already, I'm assuming I couldn't use a through-glass type of antenna.

Well-Known Member
This question needs a photo to show what the grid looks like, exactly, and perhaps one to show where the amp is mounted. Any chance you can post some pics? I share your offense. I'm not learned in the art of making a hole through automotive glass, and that aspect of your suggestion scares me.

I'm also a bit puzzled why you say that water runs down the glass because you added tinting. Why is that?

The March Muppet

Member
I'm not learned in the art of making a hole through automotive glass, and that aspect of your suggestion scares me.
Oh yes. One immediate "NOOOO.." - that hatch glass is tempered. Attempting to drill will result in exactly 263,414 little gems of hatch glass all over the place.

I agree .. tint is a film applied to the inside surface. Uncertain how this affects anything.

They put the amp between the glass and the metal surround of the hatch
Not MB savvy, but I can't picture this. If anything the module would be in the hatch frame, and accessible via trim removal. although nothing would surprise me anymore. Perhaps a bit white trash - but see if you can access the module, and if so glop a massive booger of GE silicone II over it?

nlinesk8s

New Member
HI all. It took a few weeks to get through Christmas and get back to this. I have pics but the system says I they are too large to insert or attach. I'm trying to insert a link:

The amp left is attached to the antenna connection, two boxes that fit up against the grid on the hatchback glass. Understand not drilling through glass; I could certainly run a couple of wires around the edge of the glass to the existing connections.

My problem is that the amp and antenna no longer work, and are NLA from Mercedes. Actually the parts are available, but really expensive, and there's no guarantee it'll work anyways.

I can probably come up with a circuit diagram of this area.

Well-Known Member
I see the two coax cables coming out of one of the boxes, and I see how that can couple to the base of that vertical conductor on the glass. So, I presume that this box has the amp in it. I'm not clear on what the other box is as there are no coax wires, so can I assume that the other box has to do with the defrosting? Now that you have the box free of the glass, why can't you free up the cable and remove the box to repair the amp inside? I understand replacing it is too expensive, but repair seems a lot cleaner a solution than replacing with some other design. So, let's see how to disconnect the wires that come out of the box. Once you have the box free, we can see about repair.

nlinesk8s

New Member
It's my understanding that the smaller box is the antenna connection. You're right it uses the defroster grid, but isn't powering it. I'll disconnect and open up the boxes and post some more pics.

Well-Known Member
A quick question. Do you have a tinting film on this glass now? I can't quite tell from the pics. If so, when did this film go on and did this not affect the performance of the antenna? I thought that tinting film might have some conductive properties which would mess up the performance of the antenna.

atferrari

Well-Known Member
When I was active as a ham, I noticed an antenna (VHF 2-m band, IIRC) installed on the glass, coupled capacitively, IIRC again, with no holes at all. About 20++ years ago.

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nlinesk8s

New Member
I"m going to get the units off and take some pics this weekend. The windows are tinted, and you're right that some tints mess up the antenna. In this case the normal failure is that they open the hatch to do tinting, and the fluid used runs down into the electronics (which aren't visible with the trim installed).