[Elecraft] Remote Antenna Tuner

[Vic Rosenthal]

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