> Edward McCann <edwmccann@yahoo.com wrote:
> Could you address the difference between "tuned" and "untuned" feeders to
> which refer.
> I have yet to read a description of this phenomena or technique that I can
> honestly say I fully understand, or that I can repeat to any other interested
> party.
"Tuned feedline" means the load on the transmission line is different from the
surge impedance, so it operates with substantial standing waves and normally
must be used with some kind of a tuner. The feedline length is usually some
integral multiple of a quarter wave, measured out just like you would the
length of each leg of a dipole.
"Untuned feedline" means the load is matched to the surge impedance of the
transmission line so that it operates at or close to 1:1 SWR (no standing waves
on the line). It can be any length, and if the output impedance of the
transmitter, the surge impedance of the transmission line, and the impedance
the load presents to the transmission line all match each other, no tuner is
needed. Coax is nearly always run as an untuned, or matched line, since loss
increases rapidly with increased SWR. Open wire line can be run at high SWR,
up to 10:1 or sometimes more, without serious loss, although the matching
network must be re-tuned when you QSY beyond a certain limit. Open wire line
is nearly always used for a tuned feedline, although that stuff they call
"window line" can be used as well, but it doesn't perform quite as well as
true OWL.
Don k4kyv
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