I am researching hidden antenna options for the 914 stereo and a number of times in searches I have found reference to a person or people here who have used their rear window defroster as a stereo antenna.

What I haven't been able to find out is who did it, and how well it actually works. Anybody want to fess up?

I know some modern cars have antennae built into windows in this way, but I don't know if they are using the same grid or a separate wire. Although I suppose that heating up your stereo antenna with an electrical current might cause some radio interference....

Dave,
I have'nt done it, but it would be kinda cool if someone pipped up. In 20 years, I've never used the defroster to defrost.
M

i think it was bleyseng that did that....

QUOTE (balljoint @ Feb 13 2006, 05:12 PM)

Paging Doctor Bleyseng Doctor Bleyseng you have a telephone call.

they dont have red courtesy phones in suriname

Bump!!!

Bump!!!!!!

Most windshield antennas are a dipole. Need to connect in the center for that and to tune the lengths of the wires to a half or quarter wave of the desired frequency.

Lookit a TV antenna, no not a dish you young pups, a TV antenna. Sucker is a buncha dipoles of different lengths. Different lengths are tuned to different frequencies (channel 2, 3, 4, 5, etc plus uhf).

Those that know, they work better when you rotate them towards the signal.

Oh yeah, now they would work oh so much mo better iffin they were made of Titanium and painted yellow.....

Jim Thorosun back on rennlist gave me a writeup on how to do this several years ago, but that is in storage somewhere. And no, I haven't done it.

My old 92 Nissan pickup had its antenna applied to the windshield and it seemed to work fine with decent reception. Does anyone make a surface applied antenna that could be located on the rear window?

My new 05 Nissan pickup has a standard whip antenna on the right front fender and it also seems to work fine. This antenna is relatively short fixed length. It looks like a vertical wire with a second wire spiral wound the lenght of it with a black plastic coating. What's up with that?

You could get some copper tape like this and put a strip across your windshield. Solder the end to the center conductor of a piece of thin coax, like RG-316 (HERE) and then to your radio.

Paint a thin coat of clear epoxy over it and you'd have a pretty decent antenna. As far as length goes, you could make it 1/4 wave centered at 98 MHz (center of the FM band) which has a wavelength of 3.05 meters. So 1/4 wave would be 2 and a half feet, or 30 inches. In theory a quarter wave antenna needs a ground plane, so you could tie the shield of the coax to the chassis of the car. However, because the antenna is so close to other metal it is a total compromise anyway and probably doesn't make much of a difference.

-Tony

QUOTE (maf914 @ Feb 14 2006, 01:36 PM)

It looks like a vertical wire with a second wire spiral wound the lenght of it with a black plastic coating. What's up with that?

It's probably a fiberglass rod with a wire of tuned length wrapped around it. I thought that auto antennas were just long wire (whip) antennas with the chassis as the ground plane, not really a dipole. I'm not sure of the one on the window, i do know that many of them include an RF amplifier and they are more "active" type antennas.

My guess is that nearly all automotive radio antennas are some form of quarter wave ground plane vertical. The car makes a great ground 'plane' and they appear to be roughly 30 inches in length. A spiral is likely just a way to shorten the length by packing it in a tighter space. It sorta works.

I actually doubt that many automotive FM radio antennas are active. Active antennas are mostly reserved to high frequency (> 1 GHz) where the loss of the coaxial cable to the receiver has an impact on noise figure. GPS antennas and Xm radio antennas are active because of this. FM radio is at ~100 MHz where a few feet of coax doesn't make much difference.

-Tony

the spiral is wrapped around the antenna to reduce a whistling noise at speed. if i'm not mistaken, BMW came up with this

I worked on a hidden antenna in a semi once.

Sucker was an 8 foot dish mounted inside the trailer and could be pivoted to lock in on any satellite a la James Bond.

That hidden enuf for ya?

Ken

Antennas are strange beasts. I once bought a set of rabbit ears for my TV, calculated the ideal dipole length for a given station, oriented it for maximal reception from the transmitter, and when that worked like crap I tried every other position imaginable. I chucked the thing and tried ten feet of kinked Romex lying on the floor and the reception was amazing. On my Saab, the power antenna that raises every time I turn on the CD player (pause to think about that one) eventually crapped out. Since it wouldn't retract and looked awful, I removed it. Reception is pretty much the same - haven't replaced it in a year. I'm not saying that Maxwell's equations don't aply (evolution is taking enough heat as it is...) but in the real world there are so many complications that random luck can often be almost as good as a carefully engineered solution. Take my dental fillings for example....

Anyway, I'd say the thing to do is find a piece of coax, hook it up to your radio, and touch the center conductor to the defroster wire. Make sure it isn't at 12V first. I'd be amazed if you didn't get something. Whether its good enough is anybodys guess.

Actually, putting a ~10000 pF, >15V capacitor in series between the defroster wire and the coax would allow you to use the defroster and the radio at the same time.