On Tue, 08 Nov 2005 15:33:01 GMT, Cecil Moore wrote:

Owen Duffy wrote:

Cecil Moore wrote:
If 100m (325 feet) of ladder-line results in 6dB loss, then a more
realistic 75 feet of ladder-line will result in about 1.4 dB of loss.

Close, I make it 2.2dB.

What matched line loss are you using? The wireman says that line
has about 0.2 dB of matched line loss per 100 ft at 30 MHz. According
to the chart in my ARRL Antenna Book, an SWR of 25:1 at the load
would cause about 1.5 dB loss in 75 feet.

I am using Wes's characterisation of Wireman 551. Dan's TLDETAILS prog
or my online calculator ( http://www.vk1od.net/tl/tllce.php ) both use
(slightly different) models derived from Wes's published measurements.

I don't have the ARRL Antenna Book with me at the moment, but I
suspect it is not based on the same Matched Line Loss model, and does
not estimate loss from the actual reflection coefficients but from an
"average SWR" model which gives an averaged loss per unit length that
doesn't take account of the fact that loss is usually highest in the
region of current maxima.

My calculator produces a figure of 2.2 dB for your example. I haven't
rechecked Dan's this morning, but it is close.

Grab Dan's calculator or mine and try it out. Dan's is really neat and
a stand-alone Windows app, my online calc has less graphics, doesn't
display (or even calculate SWR), knows about more transmission lines,
and only needs a browser to access it. I use them both.

In my 100m of W551 with a 16+j0 load at 30MHz, the loss in one metre
of line nearest the load is over 4%, the good news is that since 75%
of the transmitter power is already lost, the weighted effect of that
4.3% is nearer 1% of tx output.


... waiting for me to forget to cross an 'i' or dot a 't'.

Of course I don't, otherwise I would have mentioned ...!

Did you miss the humor?

Must have.

73
Owen
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