[Elecraft] Remote Antenna Tuner

Sun Sep 7 20:27:00 2003

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?=20


-----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:
   >>=20
   >>> I concur wholeheartedly. The antenna tuner needs to be at the =
feedpoint.
   >>>
   >>=20
   >> Where did you get such a strange idea re "needs"?  It may seem=20
   >> intuitively obvious but it is not true.
   >
   >There are situations in which the antenna tuner MUST be at the =
feedpoint=20
   >for efficient operation.  For example, suppose you have a 7 Mhz =
dipole,=20
   >coax fed with RG/8U, 100' from the rig.  You want to use it on 14MHz =
as=20
   >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=20
   >to SWR if the tuner was adjusted properly.
   >
   >Now put the tuner at the rig.  If the impedance of the antenna on =
14MHz=20
   >is 2000 ohms the SWR on the coax would be about 50:1, although the =
rig,=20
   >of course, would see 1:1.  Additional loss on the coax due to SWR =
would=20
   >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=20
   >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=20
   >the antenna, feeding it with balanced line, etc.  The balanced line=20
   >solution is not as simple as it looks, though, because you need to =
use a=20
   >balanced tuner or a balun that will be effective over a very wide =
range=20
   >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=20
   >looking into impedances that range from 10 to 2000 ohms (which can =
be=20
   >the case when trying to feed a single antenna on all bands).
   >
   >Another case where the tuner at the feedpoint is very practical is=20
   >feeding, say, a 33' whip antenna on all bands.   The losses on 14 =
MHz=20
   >would be similar to the example above, but balanced line would be=20
   >impractical (because you would need the non-existent wide-range =
balun at=20
   >the antenna base).
   >
   >It can be very useful to put a tuner at the feedpoint!
   >
   >Vic K2VCO
   >
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