Topband: Phase and Polarity -- They are Very Different

[Jim Brown]

On 2/3/2013 10:55 PM, Eric NO3M wrote:
> also the phase inverter

At the risk of being a PTA, let me remind all that phase is a 
continuously variable quantity that is directly related to frequency and 
time. It cannot be "inverted" or "reversed."

There is another parameter called "polarity," and it can be inverted by 
reversing the wiring in a circuit (often using a two-winding 
transformer), or by running through an inverting amplifier. Polarity 
does not vary with frequency.

In the old days, when almost everyone here also used the word "phase" to 
describe both things, but they are very different. That's unfortunate, 
because it leads to most of us failing to realize that simply reversing 
polarity in a transformer makes the cancellation not sensitive to 
frequency, while cancellation produced by a half wavelength of 
transmission line will be sensitive to frequency.  Further, the 
half-wave line will act as a resonant circuit, and can, in many 
situations, be used to behave in a manner that it compensates for 
resonance in an antenna.

The late Dick Heyser, a scientist at JPL and inventor of Time Delay 
Sprectrometry, introduced those of us in the pro audio world to this 
difference back in the 70s, and it helped us understand some rather 
complex acoustic relationships.  It is equally important in the RF 
world, and it is very important in the design of any directional antenna 
system.

73, Jim K9YC.