The 'E' Type Forum

A bit of background.

I definitely don’t want a body mounted aerial or an unsightly ( only my opinion) DAB aerial that sticks on the inside of the windscreen.
Pilkington don’t do a screen with a DAB aerial and to be honest I’m not sure I want an expensive screen that would need replacing with the same should it get broken even with a built in FM aerial and converter.

I would much prefer the aerial to be independent.

From research a hidden FM aerial with a DAB converter doesn’t offer particularly good reception.

Housebound recovering from surgery, my thoughts keep returning to using the centre screen support on an OTS as an aerial.
This would mean isolating it top and bottom from the screen top and the bulkhead bracket respectively.
The engineering and fabrication of a new custom support is not a problem however my knowledge of radio aerials, waves, receivers and the likes is zero.

Any amateur radio boffins out there with thoughts and input on this much appreciated.
I really want to make this work as I think it would be a neat solution.

From Google.

“The best mobile performer is an aerial cut to the correct
resonant length mounted as central as possible on the car roof. This is
commonly known as a Marconi quarter wave, whose length is 300 divided by
the frequency in question the result divided by 4 , and then multiplied
by .95 is the length in millimetres the aerial needs to be for the
frequency concerned.”


Simon

Your idea has merit but the challenge comes from the fact that radio frequency waves are no respecter of conduction or isolation in the simple way that 12 volts DC is.

So, you could construct the central screen support to have a length of conducting material taken from the formula you've quoted from your google search for 200MHz (30+cms) and have an insulating material at either end to make up the total difference for the OTS screen support. Unfortunately in RF terms the length of your chosen conductor will still couple into the surrounding metal frame of the windscreen changing the effective length of your conductor and the base of the aerial meaning a lot of trial and error could be needed to find the best length of conductor for use in an E type OTS application.

A possible quicker way might be to purchase a combined DAB/VHF bee-sting antenna - there are several on eBay. Firstly jury rig it to top of the boot on your OTS and drive around and see what quality of reception you get. Some DAB receivers will display received signal strength which would be particularly helpful here. This gives you your baseline performance. Then remove the OTS centre windscreen stay and mount the bee-sting antenna in it's place. (If you're prepared to remove the crash-pad for this experiment so much the better and mount the base of the aerial under the dash metal with the "bee-sting" sticking out).
Repeat driving around and logging reception.
Replace the centre windscreen stay leaving the antenna immediately in front.
Repeat driving around and logging reception.
At this point you may find that reception and aesthetics are acceptable. If not, and performance was acceptable with the windscreen stay removed, replace the whole windscreen stay with a non metallic version and live with the aesthetic compromise. If that compromise isn't acceptable and you did get acceptable reception with no centre stay in place, refit a non metallic centre stay and wrap a fine length of single core wire around the non metallic centre stay with the bottom end connected to the base of the bee-sting antenna. Play with multiple options of length of wire until you get the best reception.
Once you've found the best length of wire, cover all the length of your non metallic centre stay with heat shrink to hold the wire in place and license the best length of wire to the rest of us to cover the hours you'll now have spent in search of perfection

John,

Thanks for the detailed reply and especially the fact that although insulated from the metal screen top, it may “change the effective length “.
I’ve ordered a couple of aerials from these guys. www.dabonwheels.co.uk , to as you say experiment with. They have quite a comprehensive selection with ratings for reception if anyone else is after a DAB aerial or converter.

Thanks again,

Simon