I'm about to start trials with different aerials in the car to obtain FM/AM/TMC for a Columbus as I only have a roof mounted 'whip' aerial that is failing.

1. As a trial I want to test the amps I have from a Touran for their relative performance (one is FM only the other FM/AM) and want to connect it to a mock wire aerial. Is there an 'ideal' wire to use when making aerials?

2. I'm going to try various lengths of wire in various patterns - I think the terminology is di-pole aerial but my reading so far on the net is not going into my head! I believe that 32" is a good length but is this either side of centre (64" in total) or 16" either side of centre? Can anyone point me in the direction of (straightforward) advice on aerial patterns & lengths for radio reception?

3. Assuming this goes well, I'm going to paint the respectives lines on the glass windows using conductive paint. I only have silver conductive paint at the moment though. Does anyone know where I can get a conductive paint that matches the colour of the rear window demister lines?

There are some very knowledgeable people on this forum so in hopeful that at least one of you will be able to help me.

Thanks.

First of all the easy question! generally the best wire to use for an aerial would be a solid conductor, although for reception it's not so important.

As for aerial length, that’s a little more complicated. As a rule of thumb the aerial size or length should be as close as possible to the wave length of the signal being received. There are lots of tables on the net but if you pick a frequency mid of the FM band say 97Mhz that would give you a wave length of approx. 3 metres. Therefore a half wave dipole would have a total length of approx. 1.5 metres.

A dipole is centre fed so each half of the dipole would be 0.75m or 29.5 ins. (59ins overall.)

Most aerials that you see on older cars, such as the typical telescopic type, are half of a dipole (ish) with the cars body acting as the other half, or ground plane, which is why it's pretty important to have a good earth at the aerial base.

Cars that have a small aerial such as most modern cars, are very inefficient and that’s why they will usually have an amplifier to try and compensate for the poopy signal.

If you fabricate a dipole you also need to take in to account polarisation. Most car aerials are vertical as this presents itself to the signal no matter which way the car is pointing. If you have a dipole stretched horizontally across the back windscreen at some point it's gona be end on to the aerial and give you a poor signal or fading.

You might be better off shaping it as an inverted V or W hopefully, this will make it a bit better.. and smaller.

At the end of the day the best aerial you can get is a plain old vertical bit of stainless fixed to the bodywork with a good earth at the base mount, but unfortunately it's the least aesthetic and nobody wants to drill their car.

Hope this helps you out a bit.

That's a great response. Thank you.

It helps me with questions 1 & 2 and confirms a couple of things for me.

My plan was to use copper conductive paint (after some test runs with wire taped to the glass) to replicate the OE window aerials on both sides of an extate with one using an AM/FM amp and the other an FM amp (both hijacked from a Touran).

Coincidentally the Touran has both aerials identical and are inverted 'W' patterns as you suggested.

The Skoda Octavia one is different - more like a back to front & twisted 'E'.

Just awaiting a cable adaptet to be delivered and then on with the fitting and testing I think.

OK, good luck with this. Hidden aerials are always a compromise. You can buy some sticky back copper tape on ebay. People use it for making up model car race tracks and other such things. However it's generally only available in 1/4" width min. You could try cutting it down (careful with that stanley knife!) but it would still be thicker than the heating elements. Might be good to experiment with though, and you can just peel it off again if you didn't like it. A bit less permanant than paint.

Good luck

Steve.

The patterns on the glass are made up of two prints: the orangey brown colour you see, then overprinted with the conductor usually silverish.

You can buy self adhesive tape in thinner sections, but I don't know where. I've seen it used for doing exactly what you say, making up test antennas.

Thanks for the information lowedb & citori. Very useful and I'll look into that tape concept as a means if testing it out.

I have some silver conductive 'paint' already which should work, but I'm not sure how it will look with silver lines... As its the side windows and the cars silver anyway, I could probably get away with it.

How is the silver overlaid on the copper? I can't see any evidence if it on the demisters or on the aerial I looked at last week?

Still waiting for the cable to arrive (from China) then I'll start taking trim off to get the cables in and playing with 'aerials'.

Keep any info on serial patterns / lengths coming please. And any sources of this 'tape' or copper coloured conductive paint.

The conductive layer is added afterwards as a second screen print.

Just checked the HRW on mine and it's very hard to make it out as it's on the inside only. The lines are so thin the light coming through from behind (with the tailgate open) makes them just look brown. However in one corner there's an antenna pattern that's a fraction wider, and you can see on that it's silvery on the inside.