[Elecraft] Remote Antenna Tuner
Bill Johnson (WR Johnson Consulting)
[email protected]
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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