[TowerTalk] tuners and power rating

[Paul Christensen]

Steve,

I just ran the numbers referred to by Owen, only I used RG-58 instead of 
LMR-400:

http://vk1od.net/transmissionline/VSWR/aldv.htm

Since the QST author did not specify the coax type, the outcome for RG-58 is 
closer to the mid-point of their respective results.  Here's the loss I get 
with RG-58:

40 ft of RG-58:  9.6 dB
300 ft of Wireman  450 ohm windowed ladder line:  3.5 dB

Difference:  6.1 dB
VK1OD's difference:  2.4 dB (I get the same result with LMR-400)
QST author's difference:  10.6 dB

I suspect the author got that result from: (1) relying on the graph; (2) 
using figures from low-loss non-windowed or tubular 450 ohm line where loss 
is less; and (3) perhaps RG-58 was used for the QST comparison rather than a 
low-loss coax type like LMR-400.

Just for fun, I then ran the calculation with 300 ft of RG-58 for an 
apples-to-apples comparison of line length for a long run.  Total loss is a 
whopping 19.1 dB.  In fact, the return loss is so high, the VSWR at the 
transmitter is 1.66:1.  With that much loss, darn near anything you do to 
the end of the line would probably keep the SWR under 2:1.  With LMR-400, 
300 ft of loss is 13.5 dB versus 3.5 dB for somewhat lossy windowed line.

Paul, W9AC

----- Original Message ----- 
From: "Steve Hunt" <steve at karinya.net>
To: <towertalk at contesting.com>
Sent: Wednesday, December 01, 2010 10:57 AM
Subject: Re: [TowerTalk] tuners and power rating


> Paul,
>
> I checked that page of Owen's earlier for a chart which shows the losses
> at various distances from a mismatched load; it was the epitomy of "a
> picture paints a thousand words"! Unfortunately Owen seems to have
> removed it as part of his recent site re-vamp.
>
> 73,
> Steve G3TXQ