[Elecraft] ATU vs. External Tuner

[John Buck]

Frank,

Since the dipole is in the attic, you are probably not getting perfect 
swr without a tuner.  The antenna is a compromise unless you have a very 
large attic with little metal near by.  If you have trimmed it for 
resonance at 40 meters I assume it is quite a bit shorter than a 
standard dipole due the proximity of the roof and wood work.

If the dipole is actually resonant at 40 meters then it will work poorly 
on 20 meters even if you can match it at the radio with some combination 
of feedline and tuner.  Please note that a perfect dipole up high in the 
clear will not be 1 to 1 swr at resonance but will be 70 to 90 ohms.  Do 
not fall into the trap of trying to obtain a perfect match on every band. 

I would try a non resonant length (g5rv style) fed with coax.  It will 
be more effective on multiple bands and the SWR will not be too high to 
tune as it is on the second harmonic with a resonant dipole.  The 
antenna center impedance of the g5rv lengths (102' or 88' if in the 
clear) avoids extreme high impedances on several of the HF bands.   The 
coax losses should be be acceptable on most bands.  I would certainly 
try that with the K3 tuner   If you have carefully trimmed the 40 meter 
for resonance in place in the attic, try adding about 25% length and if 
necessary folding the ends to fit.  There is nothing wrong with trying 
fan dipoles if you have the space and can trim appropriately.

I am sure others will correct my ball park numbers.  I also would not 
get carried away about the perfect feedline length for feeding a g5rv.  
The best feed line is the shortest one that goes from the antenna to the 
tuner.

That said, if the coax line is very long, then a remote tuner is nice.
The K3 tuner is excellent.  I would use it .  If you fall into a good 
automatic remote tuner use that.
But consider the fact that resonant antennas to not necessarily radiate 
better than properly tuned non resonant lengths.

John KH7T

Frank MacDonell wrote:
> I have a k3 with internal antenna tuner connected to a 40 meter dipole
> in the attic. Will the internal ATU work for me visiting other bands
> or would I be better off installing a tuner between the rig and the
> antenna? Is an auto tuner more preferred than automatic? Thanks to all
> for your time.
>
>