[TowerTalk] "Antenna Tuner"

[Gary Schafer]

Further to your point Dave:

It is easier to see if we consider a 1/2 wave length of coax for the feed
line.

If one were to have a 1/2 wave length of coax between the antenna and the
tuner, then anything that is done at one end of the coax looks exactly the
same at the other end.

If the antenna looks inductive at its feed point then that same inductive
reactance will be seen at the transmitter end of the coax. 

We can add capacitance at the antenna or shorten the antenna to cancel the
inductive reactance (bring it into resonance). The same change will be seen
at the transmitter end of the 1/2 wave length of coax.

Rather than add the capacitance at the antenna end or shorten the antenna we
could add the same amount of capacitance at the transmitter end of the coax
which will be seen at the antenna end of the coax. The end result is exactly
the same. The antenna feed point is brought into resonance.

With a length of coax other than a 1/2 wave length the end result is the
same except we need a different value of reactance at the transmitter end
depending on how far away from a 1/2 wave length the coax is as the
reactance will be transformed to a different value.

Keeping in mind that any change in reactance at one end of the coax is also
seen at the other end we can look at it as just impedance matching or is
that reactance change that is hooked to the antenna actually tuning the
antenna..

For those interested in further reading look at Walt Maxwell's article "my
antenna tuner really does tune my antenna".

It is just a matter of how you want to look at the problem as to what tunes
what.

73
Gary  K4FMX



> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> David Gilbert
> Sent: Saturday, May 03, 2014 10:12 PM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] "Antenna Tuner"
> 
> 
> With all due respect, that's not a particularly valid distinction.
> 
> For example, I can have a non-resonant antenna fed by 100 feet of coax
> (call it Coax A) that presents a reactive load to my transmitter.  I can
> then attach a separate 100 foot length of coax (call it Coax B) to the
> "feedpoint" of the antenna and put some kind of reactive network at the
> other end of Coax B that now results in a matched load to Coax A, and
> therefore to my transmitter.
> 
> Or I can use a tuner in the shack to do EXACTLY the same thing ... 100
> feet away from the antenna ... except that I just happen to be coupling
> my power to the same length of coax and network that is providing the
> matching.
> 
> There is zero electrical difference between the two situations I
> describe above.  There is zero difference between the transformation
> that a tuner creates and that which a matching network does ... no
> matter where the matching happens to be located.  The ONLY difference is
> that the less transmission line you have between your antenna and the
> matching network the less overall system loss there will probably be.
> That's it ... period.  It is purely semantics what we decide to call the
> various versions of what actually perform the exact same electrical
> function ... there is no difference network-wise.
> 
> Dave   AB7E
> 
> 
> 
> On 5/3/2014 9:17 AM, WA3GIN in King George, VA wrote:
> > Dave, with ipmost and all due respect those mentioned auto-tuners do
> > NOT adjust the resonance of the antenna... they are purely impedance
> > matching devices... some do understand the terminology and the physics
> > ;-)  You can dumb down the tech talk but that doesn't change the
> fact...K
> >
> > 73,
> > dave
> > wa3gin
> >
> > ----- Original Message ----- From: "David Gilbert"
> > <xdavid at cis-broadband.com>
> > To: <towertalk at contesting.com>
> > Sent: Saturday, May 03, 2014 11:38 AM
> > Subject: Re: [TowerTalk] "Antenna Tuner"
> >
> >
> >>
> >> They adjust the resonance of the >system<, and therefore are indeed
> >> "tuners".  It's all the same thing, except of course for the feedline
> >> effects of SWR.
> >>
> >> That being said, I have never understood why so many hams get hung up
> >> on the semantics of the terminology instead of bothering to
> >> understand what's really going on.
> >>
> >> Dave   AB7E
> >>
> >>
> >> On 5/3/2014 5:56 AM, Marsh Stewart wrote:
> >>> Someone posted the following on the subject of antenna tuners: "They
> >>> aren't
> >>> adjusting the resonance of the antenna, so what are they tuning?"
> >>>
> >>> When I adjust the capacitance and inductance of my "antenna tuner"
> my
> >>> antenna does not change length or height, and the length of the
> >>> feedline
> >>> does not change. Could it be because it is not really an "antenna
> >>> tuner" but
> >>> is actually an impedance matching network?
> >>>
> >>> Marsh, KA5M
> >>>
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