On Sat, 2008-07-05 at 21:52 -0700, Jim WA9YSD wrote:
> What is the difference between putting a remote antenna tuner at the feed
> point of the antenna verses at the end of the feed line like most hams have
> for their installation?
> Keep The Faith, Jim K9TF/WA9YSD
Tuner at the antenna feed point operates the feedline in a nearly
matched condition (some tuners are happy with 1.5:1 SWR on their input)
that minimizes the feed line losses. Tuner at the antenna feed point can
tune the antenna over a wider frequency/impedance range with the same
components than the tuner at the transmitter tuning through the
feedline. It may be argued that the tuner at the antenna actually
resonates the antenna and so improves its radiation efficiency at some
cost from losses in the tuner. For sure that resonating effect on
radiation efficiency is greater with the tuner at the antenna than at
the transmitter because of the feedline losses.
It takes a significant SWR and significant loss in the feedline for a
high SWR to cause much additional loss. I don't think its a linear
function of SWR. Nearly every ARRL handbook has a graph of the added
loss vs initial line loss and SWR.
Trouble with the antenna tuner at the antenna feed point is that it has
moving parts (roller coils, motor, capacitors, or a gaggle of relays) in
a position inconvenient for maintenance and repair. On a naval ship
there are always plenty of new recruits trained and willing to scramble
up the mast to swap out the broken (or melted) tuner. Not all ham shacks
are so well equipped.
73, Jerry, K0CQ
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