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An antenna question--43 ft vertical
In article ,
Wayne wrote: On the 43 foot vertical it could be that the 4:1 unun provides a lower amount of SWR induced additional feedline loss on high Z feedpoints. Of course, the unun might increase the SWR induced additional feedline loss for smaller Z. From the charts, that kinda does appear to be the case. Add into consideration the fact that losses go up with the square of the current. Another issue is the other aspect of SWR - voltage. If you're trying to run "legal limit" or close to it, high SWR on the feedline coax could exceed the voltage rating of the coax dielectric, and you'd get arcing in the coax (or arcing at the connector between your feedline and shack tuner). Installing a hefty 4:1 unun right at the antenna would reduce the worse-case voltage on the feedline, and inside the shack tuner considerably. Depending on feedline length, that might be even more of a consideration than the increase in peak feedline current and the associated I^2*R losses. |
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An antenna question--43 ft vertical
"Dave Platt" wrote in message ... In article , Wayne wrote: On the 43 foot vertical it could be that the 4:1 unun provides a lower amount of SWR induced additional feedline loss on high Z feedpoints. Of course, the unun might increase the SWR induced additional feedline loss for smaller Z. From the charts, that kinda does appear to be the case. Add into consideration the fact that losses go up with the square of the current. Another issue is the other aspect of SWR - voltage. If you're trying to run "legal limit" or close to it, high SWR on the feedline coax could exceed the voltage rating of the coax dielectric, and you'd get arcing in the coax (or arcing at the connector between your feedline and shack tuner). Installing a hefty 4:1 unun right at the antenna would reduce the worse-case voltage on the feedline, and inside the shack tuner considerably. Depending on feedline length, that might be even more of a consideration than the increase in peak feedline current and the associated I^2*R losses. Good points. I'm running low powers at the moment, but there was a time where I burned up a lot of stuff running a KW |
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