[Elecraft] OT: Now Balun effectiveness

[Darrell Bellerive]

Mike,

I can relate to this! I too have felt the wrath of the SWR police.

There seems to be a lot of confusion about SWR and losses. Maxwell's
book Reflections makes it clear that SWR is not a be all end all
measurement, and that SWR and feedline loss can be an acceptable design
compromise. But as you point out at 93.9:1 SWR the loss over 150 feet of
coax is 93.4%. Hardly acceptable at all to me, but I suppose if someone
had a legal limit power amplifier and wanted QRP ERP levels, it would
work.

I kept worrying that I had missed something new in multiband antenna
design; That someone had found a way to use coax and a balun to make a
feedline that had losses similar to open wire feeder over the entire
MF/HF spectrum regardless of mismatch.

There is also confusion as to the use of open wire feeder between the
antenna and tuner or mounting the tuner at the feedpoint of the antenna.
Some maintain that the feedline will contribute to the diversity of the
mismatch where others content that it is irrelevant. I would expect that
the losses would be lowest by mounting the tuner at the feedpoint, but
the losses in the open wire feeder may be low enough to live with a more
convenient place to mount the tuner. There is a need for more empirical
research.

So all in all I am still a big fan of the remote tuner. The big question
in my mind is whether Elecraft will offer such a product.

Darrell VE7CLA K@ #1973

On Wed, 2004-03-24 at 14:53, Mike Harris wrote:
> I'm surprised the SWR police haven't descended upon this.  Last time I
> suggested that the antenna was the best place to put the tuner it really
> wound them up.
> 
> Try running the feed impedance numbers of the Cebik 44ft doublet through
> something like TLA which is bundled with the ARRL Antenna Book, Smith
> Chart or even model it in NEC.   You will discover that feeding it direct
> with 50 ohm cable gives SWR's ranging from 1.45 up to 93.9  OK select say
> 150 feet of RG-213 and on those bands, shock horror, anything between
> 17.6% to 93.4% total line loss.  At the rig end SWR's in the range 1.36 up
> to 7.66 which are easily matched by the KAT100 but actually the whole
> antenna is a dead loss on 5 out of 7 bands if fed with 50ohm co-ax.
>