Thanks Steve. That makes perfect sense. What's a mystery is why the loss
attributed to SWR under that condition shows as a negative value in TLD,
albeit a small amount. The inverse of loss is...well, gain!
----- Original Message -----
From: "Steve Hunt" <firstname.lastname@example.org>
Sent: Tuesday, November 30, 2010 1:24 PM
Subject: Re: [TowerTalk] tuners and power rating
> It's not really counter-intuitive when you remember that at HF the vast
> majority of feedline losses are I*I*R losses and therefore driven by the
> current that is being carried. If we have a 150 Ohm Resistive component
> to the load - no matter what its Reactance - the current into the load
> must be 57.7% that of the matched case when dissipating the same power.
> That means that *right adjacent to the load* the feedline power loss per
> unit length will be 1/3 that of the matched case. It's only further back
> along the line, where the current standing wave begins to "develop"
> higher currents, that the losses increase and eventually overtake the
> matched-line losses.
> ARRL's TLW software gets it right. Now, if they would just correct their
> hopelessly optimistic loss figures for ladderline, it would be a useful
> programme ;)
> Steve G3TXQ
> On 30/11/2010 14:09, Paul Christensen wrote:
>> TLD software appears to satisfy that test. What's interesting under your
>> test set of parameters is that power delivered to the load peaks when the
>> complex Z at the load is opposite in reactance at the Tx end, but the
>> resulting Z values are equal. For example, if you use a load of 150
>> the resulting complex Z seen at the Tx is 150-j130, resulting in 99.7% of
>> power reaching the load. The two resulting impedances are exactly equal
>> being just under 200 ohms. I am using 10 ft. of RG-213 (vf = 0.66) for
>> By contrast, under a matched condition, where the termination is 50+j0,
>> power delivered to the load is only 99.17%. Small differences for sure,
>> the result is very interesting and counterintuitive. According to TLD,
>> higher power delivered to the load under the mismatch condition is the
>> result of loss attributed solely by SWR actually going negative in value
>> (-0.024 dB).
>> Paul, W9AC
>> ----- Original Message -----
>> From: "Steve Hunt"<email@example.com>
>> Sent: Tuesday, November 30, 2010 7:29 AM
>> Subject: Re: [TowerTalk] tuners and power rating
>>> The most comprehensive calculator I know is Owen's at:
>>> A good test for a calculator is to look at the loss it predicts for 10ft
>>> of 50 Ohm coax at 3.5MHz with a 150+j0 load (VSWR=3:1); the loss should
>>> be about **half** the matched loss.
>>> Charts which imply - without any caveats - that a particular value of
>>> VSWR always adds a fixed "excess loss", are misleading and show a lack
>>> of understanding of the loss mechanisms.
>>> Steve G3TXQ
>>> On 30/11/2010 00:04, Rik van Riel wrote:
>>>> After some searching around the web, I found an online
>>>> transmission line calculator that does take these things
>>>> into account:
>>>> It does indeed give interesting and different answers
>>>> than the coax calculator I used before...
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