[TowerTalk] tuners and power rating

[Rik van Riel]

On 11/28/2010 10:56 PM, DJ7WW wrote:
> A tuner working into a 5:1 mismatch would not improve the antenna and feed
> line loss anyway.
> A tuner is the wrong approach to compensate a bad antenna design.

A 5:1 mismatch can be entirely reasonable depending on the band,
the antenna, etc...

For example on 160m and 80m it is common to have high impedances
at the band edges, because these bands are just so wide (as a
percentage of the center freq).

However, a 5:1 mismatch at 2 MHz with 100' of LMR-400 coax only
results in an SWR loss of 0.4 dB.

That 0.4dB of feedline loss (.26 of which due to SWR) may be a
perfectly reasonable tradeoff...

Now, at 29 MHz that same 5:1 SWR could be a big problem - but
you don't need to have that kind of SWR on 10m :)

You can calculate the (SWR related) feedline losses quite easily
with one of the online coax calculators, eg:

http://www.saarsham.net/coax.html

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