On Sep 24, 9:24*pm, Tim Shoppa wrote:
On Sep 23, 11:03*pm, "justme" wrote:

I GET DIFFERENT RESULTS WHEN COMPARING TO A GRAPH.

Exact impedance of ladder line is usually unimportant. It is so low-
loss, that even large impedance mismatches do not result in any
appreciable transmission line losses.

Another thing, base 10 log and natural log often are confused.

Tim N3QE

Not so!

For example in this month's QST magazine there's an article on using a
40m full-wave loop on 80m. The designer uses a series quarter-wave
section of 450 ohm ladderline to make the impedance "more manageable".
He quotes 300+j8000 at the antenna end of the ladderline. Now plug
those values into Owen's calculator, using something like Wireman 551
for the line, and you'll get 7dB of feedline loss.

73,
Steve G3TXQ

steveeh131047 wrote in news:11c60904-d961-4e70-9b60-
:

....
For example in this month's QST magazine there's an article on using a
40m full-wave loop on 80m. The designer uses a series quarter-wave
section of 450 ohm ladderline to make the impedance "more manageable".
He quotes 300+j8000 at the antenna end of the ladderline. Now plug
those values into Owen's calculator, using something like Wireman 551
for the line, and you'll get 7dB of feedline loss.

Steve,

It may even be worse than that as TLLC models skin effect in a
homogenouse conductor, and some ladder lines use copper clad steel that
will have higher loss at the low end of HF where the coating thickness is
less than several skin depths. This is especially true of the more
expensive stranded CCS types.

But, yes... QST runs stories from time to time that reinforce the myth
that ladder line is so good that you *never* need to consider its loss.

Here is are reviews of a couple of older articles discussing the relative
merits of ladder line and coax:

http://vk1od.net/blog/?p=316

http://vk1od.net/transmissionline/LOLL/

Owen

Owen,

I've e-mailed comments to the QST "Technical Correspondence" team
concerning the failure to mention ladderline losses in the loop
article - it'll be interesting to see if they respond with any
comments in a future edition.

73,
Steve G3TXQ