[Elecraft] Remote Antenna Tuner
David A. Belsley
David A. Belsley" <[email protected]
Sun Sep 7 21:50:04 2003
Yes, it matters. You want to avoid having any stretch of the feed from the
xceiver to the antenna that has a high loss with high SWR. Thus, you don't
want a situation where you have, say, xceiver, tuner, coax, antenna, where
the coax has a high SWR because it doesn't match the antenna. The tuner
will allow the K2 to see 50 ohms and behave well, but there will be
excessive loss in the coax because of the high SWR. The way around this is
to have xceiver, coax, tuner, antenna (or open wire feed line). Now the
tuner will put 50 ohms at the far end of the coax (which the K2 will
happily see), and hence there will be 1-1 SWR in the coax -- and hence no
additional loss in the coax due to high SWR.
best wishes,
dave belsley, w1euy
--On Sunday, September 7, 2003 7:21 PM -0500 "Bill Johnson (WR Johnson
Consulting)" <[email protected]> wrote:
> If the antenna doesn't match transmitter output without a tuner, does
> it really matter where the tuner is placed as long as the rig output is
> matched?
>
>
>
> -----Original Message-----
> >From: "-Vic Rosenthal" <[email protected]>
> >Sent: 9/7/03 10:05:59 AM
> >To: "Phil Wheeler" <[email protected]>
> >Cc: "Darrell Bellerive" <[email protected]>, "Kurt Cramer"
> <[email protected]>, "Mike Harris" <[email protected]>,
> "[email protected]" <[email protected]> >Subject: Re:
> [Elecraft] Remote Antenna Tuner
> >
> >Phil Wheeler wrote:
> >> Darrell Bellerive wrote:
> >>
> >>> I concur wholeheartedly. The antenna tuner needs to be at the
> feedpoint. >>>
> >>
> >> Where did you get such a strange idea re "needs"? It may seem
> >> intuitively obvious but it is not true.
> >
> >There are situations in which the antenna tuner MUST be at the
> feedpoint >for efficient operation. For example, suppose you have a
> 7 Mhz dipole, >coax fed with RG/8U, 100' from the rig. You want to
> use it on 14MHz as >well as other bands. If the antenna tuner were
> at the feedpoint the >line loss would be about 0.7 DB. There would
> be no additional loss due >to SWR if the tuner was adjusted properly.
> >
> >Now put the tuner at the rig. If the impedance of the antenna on
> 14MHz >is 2000 ohms the SWR on the coax would be about 50:1, although
> the rig, >of course, would see 1:1. Additional loss on the coax due
> to SWR would >be somewhere around 6-8 DB. In other words, less than
> 25 out of 100 >watts would reach the antenna. If you used RG58/U, a
> 1.5 DB loss would >become more than 10 DB. Only one out of 10 watts
> would reach the antenna. >
> >There are various other ways to fix the problem, such as using traps
> in >the antenna, feeding it with balanced line, etc. The balanced
> line >solution is not as simple as it looks, though, because you need
> to use a >balanced tuner or a balun that will be effective over a
> very wide range >of impedances at the tuner. AS far as I know, there
> are no balanced >AUTOMATIC tuners, and there is no balun design that
> will be effective >looking into impedances that range from 10 to 2000
> ohms (which can be >the case when trying to feed a single antenna on
> all bands).
> >
> >Another case where the tuner at the feedpoint is very practical is
> >feeding, say, a 33' whip antenna on all bands. The losses on 14 MHz
> >would be similar to the example above, but balanced line would be
> >impractical (because you would need the non-existent wide-range balun
> at >the antenna base).
> >
> >It can be very useful to put a tuner at the feedpoint!
> >
> >Vic K2VCO
> >
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----------------------------------
David A. Belsley
Professor of Economics