On Wed, 30 Nov 2005 23:42:33 GMT, Cecil Moore wrote:

Owen Duffy wrote:
Well, I think we are agreed that you made a mistake in identifying a
mistake, if I am not mistaken!

Your original mistake was in making a posting that caused me to
misunderstand. :-) Your loss calculator gives 0.762 dB loss for
90 feet of Wireman #445 with an SWR of 12.7:1 on 7.15 MHz.

Now, you're trying to trick me... did you mean Wireman 554?

It does show 0.76dB for 90' of 554 with a 30+j0 input Z at 7.15MHz.

The 0.9dB stated earlier was (as stated) for 552 which had a Zo closer
to your 380 ohms, whereas 554 is 360 ohms.


The whole excercise goes nowhere, because it seems that the 30 ohms
scenario is "hypothetical".

I knew it was thirty-something ohms so I said "30". It was
actually 38 ohms indicating an SWR at the source of 1.3:1.
That's acceptable losses for me. If I used an antenna tuner
to achieve a 1:1 match, it would probably be a wash.

Which is probably a good question. At what SWR should one
install an antenna tuner? My IC-706 seems perfectly
happy at 2:1.

Given that some radios (including the IC706-IIG) reduce drive power at
high VSWR as a protection mechanism, you may want to install an ATU to
develop full power output. My recollection is that the power output of
the IC706-IIG is significantly down at VSWR=2, but it probably also
depends on the actual load impedance.

A likely scenario could be that the radio only develops 50W of output,
and only 40W makes it to the feedpoint (assuming 1dB feed loss). The
ATU might raise that to 100W of output, less tuner loss and feed loss
giving 75 to 80W at the feedpoint. Mere fraction of an S point... but
if you have a 100W transmitter, might as well use it, and besides, the
technical challenge of achieving that goal and measuring the
achievement might be part of what amateur radio is about.

Owen
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