[Elecraft] Transmission line loss

[Mike B]

First of all, I have to congratulate the posters in the earlier thread on line
loss, etc., for prompting me to actually get my calculator & ARRL Handbook out
and read up on transmission line loss, dB calculations, etc.

My interest has come up as I'm planning on installing a flag pole vertical in my
yard, due to CCRs, and the coax run will be around 100 feet outside the house,
plus 28 feet inside.

Here's my take on line loss, and please correct me if I'm wrong.  For today's
discussion, let's assume the power is 100 watts, total run is 100 feet, that I
can tune this vertical up to 50 MHz, and the SWR at the antenna hits 5:1 (it
won't, as I'll have a remote tuner there, but just for discussion...).

Davis RF-brand "RF-9914F Bury-Flex" has a published matched line loss of 1.1
dB/100 ft at 50 MHz.  Per the Handbook, a 5:1 SWR at the load will add around
1.2 dB of loss, for a total of 2.3 dB over the run, for about 60% efficiency.
(I'm still fuzzy on the percentage calculations.)

A variety of brands of RG-8X have a matched line loss of 2.0 dB at 50 MHz per
100 ft.  A 5:1 SWR adds 1.7 dB, for a total of 3.7 dB loss, for a little over
42% efficiency.

Am I reading something wrong here, or is the 1.4 dB difference between the two
cables correct?  Can you extrapolate that to an S-meter at 6 dB/S-unit?  If so,
I'd say the 1.4 dB would be barely noticeable on the receiving end at best, and
the extra cost of lower loss coax isn't worth the money.  Operation at HF would
be even less of an difference than at 50 MHz.

I realize there may be other considerations as to the type of coax used that
could sway one's decision.  In my case, I want direct buriable, and I haven't
come across any 8X that allows this.  Longer runs and higher SWR would obviously
sway the argument as well.

RG-6 seems to be in between the RG-8X and Bury-Flex as far as loss, but the cost
may be much better (from what I've read here).

In my searching, I came across a pretty handy document from Cisco relating to dB
loss and gain:
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a00800e90fe.shtml
Thanks for your input.

73,

Mike
KW1ND