Herb Schoenbohm wrote: > Recently I purchased some video baluns to use for an FM station to > remove hum from cables feeding a composite audio single from the
I did some design work on video baluns a few years ago. They consist of a large number of turns of twisted pair on an ungapped pot core. Old fashioned analog video is best sent with DC coupling. If that cannot be done, AC coupling can be used if the low frequency response extends to something like 30 Hz. It is possible to add DC restoration to take care of the missing DC. Having said that, there is no such requirement for topband work. You can get even better isolation by using a conventional flux coupled transformer instead of a common mode choke (referred to commonly as a "balun"). I have been using Mini Circuits T1-6 and similar transformers for years in this manner for receiving antennas. I have also wound my own on binocular cores. You wind them the same as "baluns" but connect the wires differently. When you do this, the finite impedance of the ferrite is applied in shunt with the signals, and has no effect on the isolation. It is not in shunt from input to output as with the balun configuration. Rick N6RK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
