FM transmitters (make them work!)
Hello fellow audio enthusiasts. I like many of you have purchased an FM transmitter for use in my car only to find out that it is worthless. Maybe you throw it away maybe your brave and try to hack it. But who's advice is worth trusting your hardware too?
I would like this thread to be a place where those who are not sure how may come to learn some basic principles that will assist in a worthwhile hack you can be proud of. I would also like to clean up some of the bad ideas that are going around with the intent of repressing the perpetuation of ignorance.
Rule #1 Correct conductor length is mandatory for a proper antenna! Your old linksys is not a good source for an FM radio band antenna (100,000,000Hz vs 24,000,000,000Hz is a significant difference)
You want your antenna to be 1/4 wavelength. Assuming open air dielectric and a center frequency of ~100MHz(FM band 88MHz - 108MHz )
1/4 Wavelength = (Speed of light)/((4)frequency) = 0.75 meters (about 29 inches). This is a good starting point for adding a piece of wire as an antenna. The worst length you could choose is 60 inches(at this length you cancel out your signal)
Rule #2 Hanging an additional antenna off of the existing antenna creates several problems ranging from it will not work to ruining your output stage with reflected power.
For RF electronics the higher the frequency the more careful you have to be about the way you load the output. Fortunately 100MHz is relatively forgiving. However when you are trying to decide how to attach your antenna keep in mind that you need to remove whatever is currently being used as an antenna from the output before adding your own in. usually this is as simple as lifting a pin or pulling one device. You will never know how good your hack is with the old antenna still being used.
Happy hacking
Please bring questions and success stories.
I will show off my hacked transmitter later.
|
