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> How To Test Remote Key Transmitter?
kidcash
Posted: July 06, 2009 11:45 am
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Hello,

Sorry if this is the incorrect section as I did not know where to post.

The remote central locking my car has not been working. There are 2 main components. The reciever unit which is located in

the trunk and the transponder unit which is on the key. The reciever unit recieves the signal and then sends a voltage through

the wires to the door lock solenoids to lock/unlock.

The Key transmits the signal to the reciever unit. Both the key and the receiver unit are equipped with a ROM chip that has

an identical code.

I know that there is no severed wires from the reciever unit to the door locks as I can manually lock/unlock the door by

shorting the pins out on the connector.

I bought a replacement receiver unit off ebay supposed to be working and still did not solve the problem. At this point I am

suspecting it's the transmitter on the key so I began to test that.

When I pressed the button it draws voltage from the battery in it, so this demonstrates that something works inside the

circuit, but I am not sure that the signal is being transmitted. How would I test if the signal is being transmitted?

I don't know the frequency, but I think it should be around 300 or 400mhz as this is the frequency these devices commonly operate on.

Any suggestions would be great. Thanks.

This post has been edited by kidcash on July 06, 2009 11:46 am
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CWB
Posted: July 06, 2009 12:48 pm
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there are a few things that you have to know besides the operating frequency ...
the data/information impressed upon the rf signal is the first .
there is no way to do this with a dmm .
the easiest fix is to obtain an new transmitter unit and set the codes between it and the reciever so they "match" .


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kellys_eye
Posted: July 06, 2009 01:37 pm
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The simplest solution is the easiest - change the battery in the key fob.

It's not unheard of for local transmitters to 'swamp' the operation of remote key locking devices. I realise this may be difficult but could you try moving the vehicle to another location and retrying the opener?



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tekwiz
Posted: July 06, 2009 07:17 pm
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If there are any programming switches, they must be set identical in both receiver & transmitter.
A simple "RF sniffer" or field strength meter can be used to determine if the transmitter is actually transmitting.

http://i202.photobucket.com/albums/aa106/t...z2525/sniff.jpg

This is a simple RF sniffer that I built a while ago. It has only 4 components...a loop of copper wire, a meter, one capacitor, & a germanium diode. It should work for testing keyfob transmitters. Note that the transmitter has to be right next to the pickup loop, & that the transmitted signal is very short duration, so you have to be watching carefully to catch it. cool.gif


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kellys_eye
Posted: July 06, 2009 07:38 pm
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QUOTE (tekwiz @ July 06, 2009 07:17 pm)
Note that the transmitter has to be right next to the pickup loop, & that the transmitted signal is very short duration, so you have to be watching carefully to catch it. cool.gif

You ain't kidding!

Most have an output power of around 10mW and a duration of 10mS or less!!!


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