[TowerTalk] HF beam antenna decision

[Tom Rauch]

> Just curious, how is the matching done on the SteppIR so that it presents
> 1:1 SWR over the whole range. I understand the fundamental properties to
> set the length of the elements with stepper motors, but normally a yagi
has
> a lower impedance than 50 ohms at j0. Is the 1:1 shown on an SWR meter
> built up of a complex R + j or is the feed impedance really a pure 50 ohms
> resistive on all frequencies ?
>
> 73/Peter SM2CEW

Hi Peter,

I'm sure you know this but there is no possible combination of resonant
feedpoint resistance and additional X that fools a meter into reading 1:1
SWR. There is a myth that adding some reactance to pure resistance causes a
low SWR in a 50 ohm system, but that isn't true. Any noticeable reactive
component mixed in pure resistance load (even a mismatched load) would
increase SWR. If you add a -15J capacitor in series with a 35 ohms
resistance, the impedance is 35 -15j which is a HIGHER SWR than 35 -0j.

I don't know what they do, they could detune the elements from optimum gain
or F/B and instead compromise for SWR, or maybe they handle it some other
way.

Maybe someone who has a SteppIR knows what they do. I'd be interested also,
because SWR should vary a good bit from electrically close-spaced element
bands to wide-spaced element bands.

73 Tom