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Please leave me out of this. I'm mentally handicapped!
I don't know, never did know, how to use an old fashioned, mid-20th century Smith Chart. ---- Reg. "Walter Maxwell" wrote in message ... On Mon, 14 Aug 2006 07:44:10 GMT, "Lee" wrote: I`m building a QFH NOAA weathersat antenna and wish to use low loss t/v coax which is 72ohm; but is more manageable and less lossy at VHF than the 50ohm RG58 specified over a 100ft run!.... ( RF pre-amps aint cheap! )....... What are the pros and cons... can i use CT100 72/75ohm..... i believe i can but, will the impedence affect the 4 turn choke ????... Thanks. Lee......de G6ZSG..... Hi Lee, Consider this: If your QFH has a 50-ohm terminal impedance, the mismatch is only 1.44: 1. Therefore, the loss due to the mismatch is 0,14 dB, insignifiant--use the 72-ohm line and forget the miniscule mismatch. Even if the mismatch was 2:1, the reflection loss is only 0.51 dB. Concerning the 4-turn choke, nothing happens to the matching operation, because nothing inside the coax changes due to the coiling of the coax. Walt, W2DU |