75ZT Community

Today I set about sorting out the connections to the rear window of my car having borrowed some conductive epoxy resin. The drivers-side c-pillar was fairly straight forward for the TV ariel. Brown connector bonded to screen using epoxy and black (ground) spliced into grounding wire for the other box in the c-pilar (whatever that may be for).

The problem arose when I looked at the passenger-side c-pillar and I offered up the diversity amplifier box. Looking at the following picture for reference:

Please note: In the picture below (which I have borrowed) the diversity amp is the long black box from which a ribbon cable is plugged into the top of. Please ignore the red circle as this has nothing to do with my description. Also, please ignore the very bottom (ground) connector and the connector that is also a grounding connector that is bonded to the screen just below where the four diversity connectors are bonded. In essence, you are looking at the upper most four screen connections in the picture.



I cannot quite work out where all the connectors from the amp are bonded to the screen. This is what I know / can work out:-

• The bottom-most connector (from the amp) is bonded to the grounding strip.
• The top two connectors are bonded to different FM 'strips' on the glass. These are clearly visible on my own rear screen and are currently in use by the original FM/MW amp. These connections I shall resuse for the diversity amp by cutting then splicing into the cables.

What I can't work out is where the fourth connector goes (second-from-bottom from the amp). I can see no obvious point at which to bond this connector and neither can I clearly see in the picture above exactly what it should be bonded to

So - Can anyone help in identifying where this fourth connector should be bonded to?

Simon, a couple of pointers that may or may not be relevant:

1. Had you realised that the bottom connector connects to the same busbar as the ground you described. I think that's what you are saying.

2. Did you know you need to put inductors in series with the two ground wires, otherwise the signal all gets 'shorted' to earth via that ground connection.


Without going and looking and it's cold and dark, the two lower connections go to the same places as the two screen grounds (upper half, lower half) and both those grounds need the choke. The upper two connections go to the same place as with the non-div.

I'll have a better look at the weekend, as I have a screen in the garage.

Edit: looking at your photo again, you can see on that one, that there's a track that comes up from the lower earth tab right at the bottom of the picture. If you have that, follow it up and it should be your fourth connection.

Re: Fourth connector - I can just about see the track in the picture but I couldn't see one on my screen. Are there different types of screen? I'll have another look in daylight also at that.

Re: Inductors etc. No I didn't realise this. I was just following the lead from a suggested 'hack' taken from this photo (photo originally by Duotone/Dave I believe)



Would it therefore be easier to either
a) Undo the splice and bond the cable to the screen
b) Put an inductor inline (if so then what's an inductor, in this instance, and where do I get one?)

Many thanks for your guidance on this. All help gratefully appreciated

Inductors / chokes. You need the right value and they need to be capable of carrying the window current. They are in the leads on the diversity screens, so you could get them from there if someone is scrapping one. I'd solder them in line and cover in heatshrink, just like the original.

They are coils of wire around a ferrite core. They allow DC to pass through, but stop higher frequencies (like radio signals) getting past.

In fact, that's what's in the lower black box in your second picture. The power comes in to the box, and goes through inductors, before coming out and going to the window. The way it's spliced on your second photo is OK because the inductors are in the box (Except I loathe scotchlocks).

In fact, you could also get one of those filter boxes, and desolder the inductors.

Don't know if there are different screens. I assumed it was the same glass / print but just the extra wires not soldered on.

At the end of the day, to make it work, you could extend the wire from your amp down to the lower ground connector which is where it needs to connect anyway.

Well, I have spliced into the ground cable from the lower box as per the picture above. If you are saying this is adequate then I'm happy to leave it as is

I've just found and read this thread on the OC that you have contributed to heavily http://www.the75andztclub.co.uk/forum/s ... php?t=4125 Whilst it all makes perfect sense to me it also leads to me to believe that the diversity system a) isn't essential as I don't care much for the radio and b) might depend on what screen I have. Since my car is now a 2004 ZT I might be led to believe that the screen is a single coax system and not a full coax system used by the original diversity setup.

Now - interestingly I can tune into Channel 5 on the TV perfectly well, but the other stations elude me Now I'm either using the system wrong (and therefore need educating on how to operate my HiLine) or there's something wrong somewhere as around here Channel 5 is notoriously weak-signalled

Diversity is far from essential for FM radio, and it was later dropped on the 75. It solves a particular problem where you get a fluttering noise known as multipath interference, while driving. With good strong signals on FM it doesn't happen enough to bother people.

It does nothing on MW/LW and that box doesn't affect TV. I assme you have the hiline setup with the radio and TV in the boot.

Diversity is pretty important for TV, hence the two aerial leads on the TV tuner. Newer systems have four antennas instead of the two.

Try tuning the TV in a few different places. It's amazing how much difference even a few metres makes if there's a dead spot. You are getting close enough for Sutton Coldfield to be pretty strong, shame analogue TV isn't coming from Hopwas really.

You are going to need a digi tuner soon in any case. We switch over during next year remember.

Thank for the info Duncan. Yes, I have the Highline setup with tuner and radio in boot. Retrofitted too I believe but I'll have to get conformation on that as it wasn't my retrofit! I'll keep an eye out for (affordable) plug-n-play BMW digital tuners. Hopefully with the switch-over to all digital then overall signal strengths will improve. I'm not intending the TV function to be a must-have but it's nice as a "look what I got" thing

Thanks very much for your help in this!

SpongeBob wrote:(affordable) plug-n-play BMW digital tuners.

Contradiction in terms I'm afraid.

Tried to get a contact at the factory and it looked promising for a while, but my colleague has left for pastures new.....

I haven't looked yet - but I now know what to expect!