Posted by
vk4tux on
Sep 19, 2012; 11:51am
URL: http://elecraft.85.s1.nabble.com/KX3-ATU-tp7495809p7562976.html
Whether you tune the antenna or the feedline source makes a big difference
to signal passes on the feed line,
and hence feed line loss. Put the tuner at the antenna feedpoint and you are
tuning the antenna.
There is no nit picking about it, as to avoid the misconception by one
showing a 1:1 vswr at the transceiver, using a tuner there doing his coax
loss calculations at that vswr will get an incorrect result, when vswr
between tuner and antenna feedpoint maybe 5:1 or more (for example).
Tuning is adjusting a point to whatever you wish, whether it be a guitar E
note, or vswr at that point in the system, it is an adjustment at the point
of measurement. You may tune to a 1.5:1 vswr on a particular type of antenna
due to more effective radiation pattern. Despite all of your blather the
only things that matter are effective radiation and feedline losses.
~~~~That's pretty much picking nits, in my opinion. It doesn't really
matter whether you physically locate needed complex reactance at the antenna
or present it to the antenna via the transmission line physics of a feedline
... the net result that exists at the antenna is exactly the same
(neglecting transmission line losses, of course) in either case. The only
relevant distinction I can see is that "tuning" more accurately refers to
bringing something to resonance rather than also transforming it to a
different load impedance, but that falls into the category of useless
semantics for me and I can give you all sorts of examples where it would be
next to impossible to distinguish electrically where an antenna ends. The
dividing line between an antenna and the rest of the system is not at all as
definitive as you suggest, and pretending it is seems more likely to give a
false impression of how things really work than not.
73,
Dave AB7E
On 9/18/2012 11:52 PM, Adrian wrote:
> Matt, Of course I don't question Don's technical stature, however
> "tuning the antenna" is a poor choice of explanation, and can give a
> false impression to those weak on the subject. Adding 'system' would
> have been a good move as you indicate. We tune where we measure.
>
> -----Original Message-----
> From: Matt Maguire [mailto:
[hidden email]]
> Sent: Wednesday, 19 September 2012 3:35 PM
> To: vk4tux
> Cc:
[hidden email]
> Subject: Re: [Elecraft] KX3 ATU
>
>
> On 19/09/2012, at 2:48 PM, vk4tux <
[hidden email]> wrote:
>
>> Don, When you say "The ATU will tune the antenna to an acceptable
>> SWR", you are contradicting yourself, because as you rightly said the
>> tuner does not change the antenna feedpoint swr.
> It is clear from the context that Don meant the ATU will tune (ie.
> match) the antenna *system* to the radio, where the antenna system
> consists of the ATU, antenna and connecting feedline considered as a
> single unit. This of course does not mean that the VSWR is 1:1 everywhere
within that system.
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