[TowerTalk] Liberal Arts Major and Antenna Theory

[Ian White GM3SEK]

Lee Buller wrote:
> I am working on yagi design here and the program defines input 
>inpedance in imaginary numbers...such as 41.3 -j .9 ohms.  OK.  I am 
>trying to interpret that stuff.

For this application you can forget the math. Simply read it as a 
shorthand way of writing: "41.3 ohms resistive, in series with 0.9 ohms 
of capacitive reactance".

If it had been 41.3 +j0.9, you would read the "+" as meaning "inductive" 
instead of capacitive.

Also remember that the program is probably only accurate to an ohm or 
two, so don't sweat over the decimal parts of an ohm. The practical way 
to read that result is "pretty close to resonance, with a resistance of 
about 41 ohms".

Depending on the antenna and the model, the real information might be 
nothing more than: "Could be resonant somewhere in the band, with an 
impedance probably on the low side of 50".


-- 
73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek