[TowerTalk] "Antenna Tuner"

[Jim Lux]

On 5/3/14, 7:43 AM, Drax Felton wrote:
> You don't want a resonant antenna.  You want one that presents a 50 ohm non reactive load to the feed line if that's what the feed line is.
>
> Otherwise you use a matching network.
>
that depends..

if you are building a phased array (or a Yagi, which is a kind of phased 
array, relying on passive coupling among elements) then you also care 
about what reactance is being presented back to the antenna, 
particularly if you have multiple feedpoints.

For instance, one can make a 3 element beam with a variable L/C network 
in each element and get "steppIR" like performance (gain on multiple 
bands, switch front and back, etc.)


Hams are sort of lucky in that while we need wide operating bandwidth, 
our instantaneous bandwidth is quite narrow, and most hams change 
frequencies slowly (compared to a ALE or frequency hopping system).

So we have myriad ways to tune, adjust, or otherwise deal with frequency 
dependent aspects of the system: All the way from  pi networks on the 
output of a tube, manually adjusted tuners for feedlines and antennas; 
antennas that physically change size; auto tuners at either end of the 
feedline, not to mention wideband solid state amplifiers and/or 
autotuning tube amps.

That diversity of system designs and applications means that you have 
multiple terms for what is essentially the same box: an adjustable 
impedance transformer; the term used depends on historical tradition 
and/or the function it appears to perform in the current instance.