[Elecraft] OT: Now Balun effectiveness

[Mike Harris]

G'day,

| Put the remote tuner at the antenna feedpoint or feed with low-loss
parallel
| line from the remote tuner to the antenna and the losses will likely be
| small.  Bottom line - keep the SWR on the coax low and the losses will
| likely also be low - high SWR lines need to be open wire or ladderline
| balanced lines.  Keep in mind that it is not practical to go to
extremes -
| an SWR of 2:1 on most coax is quite tolerable when considering loss at
HF
| (VHF and UHF are quite different considerations - the loss becomes
greater
| as the frequency increases).

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.

So, the above quote is dead on.

Shack end ATU's can give a real false sense of what is happening.

I believe a reasonable rule of thumb is with 50 ohm cable anything outside
100R +/- j100 is potentially bad news.

Regards,

Mike VP8NO
#1400