D0T-C0M Posted February 19, 2007 Report Share Posted February 19, 2007 I use a FM transmitter in my truck and would like to use a normal FM antenna to transmit the signal. I think I will need a RF impedance matching transformer that will match the 50ohm impedance of my transmitter to the 75ohm impedance of the FM antenna. Can someone please suggest a good one that I can buy or if it isn't too difficult I would consider making one.Am I correct in assuming I would lose about 1/3 of my radiating signal if I directly connected the 50ohm FM transmitter output to the FM antenna?Does it make a difference where in the circuit I put the matching transformer? Should I connect it as close as possible to the FM transmitter and run 75ohm cable to the antenna OR should I place the matching transformer as close to the antenna as possible and run 50 ohm cable to my transmitter? Or does it make a difference?Should I be concerned about the change in temperature in regards to the matching transformer which I understand is temperature sensitive to some extent?Thanks as usaul for all your help. Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 19, 2007 Report Share Posted February 19, 2007 Hi Dot-com,Isn't your FM antenna just a whip? It impedance is affected by the size of its ground plane and anything that is near it. It might already be 50 ohms.A transformer will have some loss. The loss will be about the same as a small amount of loss from the impedance mis-match so you gain nothing and you won't be able to measure the small difference in output power caused by the impedance mis-match anyway. Quote Link to comment Share on other sites More sharing options...
D0T-C0M Posted February 19, 2007 Author Report Share Posted February 19, 2007 Ok I was told the the impedance of the stereo antenna in my truck was 75 Ohms, so I thought maybe I should match the impedances because initially I thought the signal loss would be roughly 2/3 of full power but I read up on the net while awaiting your response and I guess the signal loss from the impedance mismatch varies with the length of the wire. The wire in my truck is very short so I guess I won't need a matching transformer like you suggested as the signal loss will be mimimale.Audioguru, Thanks very much for replying.D0T-C0M Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.