Using Window Antenna as Stock Alarm Antenna?

[ndsti]

Okay, so I was searching and found this thread but it still didn't answer my question link.

I want to know if you can use the window antenna for the stock alarm antenna. I have a wiring diagram which shows 14 wires going into the alarm computer but when I looked I found 15.

If anybody can help or clearify my situation that would be great!

 

[Defiant]

Probably not. Antennas have to be tuned to the frequency they're operating on. However, it'd probably be harmless to give it a try.

 

[Locke]

Agreed.

OP: If you get more range out of it, be sure to let us know.

 

[kergilman]

Probably not. Antennas have to be tuned to the frequency they're operating on. However, it'd probably be harmless to give it a try.

Yep. Think of signal wavelength. Engineers use things like conductive loops and capacitive coupling in impedance matching circuitry to tune and match the antenna to the specific carrier frequency.

For a reference: Your cell phone operates @ a carrier freq of around 2 Ghz and the wavelength is right about 4 inches at that high frequency (Top of UHF range) and they normally match Rx impedance at 3/4 wavelength and will put your physical antenna length at about 2.5-3 inches.

FM stations carrier signals operate in the VHF range around 100Mhz and are forced to match impedance @ 1/4 wavelength which would put the wavelength at around 30 inches.

Car alarm remotes operate at around the 300MHz - 400Mhz range (Begining of UHF range). Don't know about the wavelength matching here, but actual physical wavelength would be about 3 times that of an FM antenna wavelength.

 

[Splitpi]

Whip Antenna Length And Frequency Calculator

 

[ndsti]

Right, I understand where you guys are coming from with wavelengths.

Another question I have is where is the alarm antenna located I have a wiring schematic for the stock alarm and the diagram shows a wire coming from the computer box behind the panel.

Like I stated earlier I had found 15 wires where should have only been 14. I know most common antennas use shielded wire but the one I found doesn't. If I find the shielded wire I can try my theory out.

 

[Defiant]

Page 321 shows the receiver E-42 with a single antenna wire coming off it. I've never been into one to see it, so I don't know how long it is nor other characteristics of it, but alarm receivers seem to be hit-and-miss. My Talon alarm remote works perfectly if I'm close enough to the car to touch any part of it, while the remote for my J-30 works from inside a building from 200 feet away.
An antenna wire such as this (look at R/C cars) aren't coax.

 

[ndsti]

Defiant where does your book show the wire is at? Is it coming from the receiver behind the rear drivers side panel where the rear speaker is?

Well....I guess i'll just cut the wire and see what happens....hahahaha I'll let you guys know if it helps, if it does maybe i'll post of How-To!

 

[snailspool]

Car alarm remotes operate at around the 300MHz - 400Mhz range (Begining of UHF range). Don't know about the wavelength matching here, but actual physical wavelength would be about 3 times that of an FM antenna wavelength.

Call me crazy, but wouldn't the wavelegth be shorter since the frequency is higher? In fact according to the calculator a full wave @300-400 MHZ is 32-30 inches or about the same as the quarter length of a 100mhz which is 28 inches. So in theory a radio antena is already tuned for that wavelength?

 

[Defiant]

I was only looking at the schematics, not the configuration.

 

[luv2rallye]

Defiant where does your book show the wire is at? Is it coming from the receiver behind the rear drivers side panel where the rear speaker is?

Well....I guess i'll just cut the wire and see what happens....hahahaha I'll let you guys know if it helps, if it does maybe i'll post of How-To!

My schematics show it coming out of the receiver but not where it goes and not going to any connector. I'd like to know where it goes also or does it just lie next to the receiver (which I suspect)? The rear window antenna for the radio exists only if you have keyless entry so maybe it goes there already (although I don't know why then it doesn't show that). You may actually increase the distance of operation connecting it there if it isn't already (although this may not be such a great idea since people 1 mile away may now unlock your car if they have the same code or some type of radio interference might like a lightning storm in the distance. I believe this is why they deliberately made it only work feet away).

As far as wavelength goes guys, yes there is an optimum antenna length for any frequency but that doesn't mean it wont work with the wrong length. It will just seriously degrade the signal and so will work only a few feet instead of a few miles. Since keyless entry is only intended a few feet they probably don't care much about length and perhaps even deliberately made the antenna not be the optimum length.

 

[Defiant]

It may be like the Homelink antenna, and be mounted inside the casing of the module itself.

 

[ndsti]

This project will be put on hold, I just got my new engine today so it's priority number one. I will however keep you posted once everything is sort of back together!

 

[luv2rallye]

It may be like the Homelink antenna, and be mounted inside the casing of the module itself.

Yes I would not be surprised.

 

[mnetwork]

Anyone find more info on this? I can't stand how I can't unlock my car from any sort of distance...

 

[luv2rallye]

I can't unlock mine from more than 2' away. Have you replaced the batteries in the key fob (weak batteries will seriously degrade distance).

 

[mnetwork]

I have the same thing.. like 2-4 feet away it works..

 

[turbosax2]

Amazingly, I got my panic button to work at nearly 40 feet away from my car. But then it wouldn't shut off so I had to get within like 15 ft. to turn it off. But my lock / unlock buttons don't work at 40 ft.

Do all of the buttons work at the same frequency?

 

[ndsti]

For everyone that wanted to know about this. Here's what I found i took apart the module behind the drivers side rear panel. I checked all the wires going to the module and none of them are the antenna wires. When looking at the circuitry it's self thier was no evidence of an antenna, except a small cylinder that could be an antenna. Then I took the board to an EE and he said thats probably the antenna.

From what I found you cannot use the window antenna but if you where able to remove the part on the board and figure out how to connect it all together then you might be able to.

If I come across another module I will try to attach the antenna wire or if some one has one lying around that they would want to give me that would help also.

Since the antenna on the board is less than half an inch long, for now we are stuck with a measly 4ft of coverage.