View Single Post
  #428   Report Post  
Old April 28th 07, 12:33 AM posted to rec.radio.amateur.antenna
Cecil Moore[_2_] Cecil Moore[_2_] is offline
external usenet poster
 
First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default Rotational speed

Roy Lewallen wrote:
EZNEC does not display "rotational speed". The user sets the rotational
speed of all voltage, current, and field phasors by choosing the
frequency, and it remains constant at that rate for all voltages,
currents, ...


Sorry, that is not true for *total* current. Check it out
yourself. EZNEC says the phase of the total current only
varies ~3 degrees from end to end for a 1/2WL dipole.
Kraus agrees with that.

Here's what you said: "This is the total current. It has
magnitude and phase like any other phasor, and the same
rotational speed as its components."

That is simply a false statement. And because it is
false, your current phase measurements through a loading
coil were invalid. Here's what you said:

"What I measured was a 3.1% reduction in magnitude from input to output,
with no discernible phase shift."

Of course you measured no discernible phase shift since
you were using a current that doesn't change phase. The
current that you used gives us no clue as to the phase
delay through a loading coil.

The phase of the total current is naturally related to
the rotational speed and it is almost unchanging, i.e.
the total current doesn't rotate by more than ~3 degrees.
It certainly does NOT rotate at omega*t.

That is one thing that makes standing-wave current quite
different from traveling wave current. You used standing
wave current to try to measure the phase shift through
a loading coil. Since standing wave current doesn't change
phase by more than ~3 degrees along the entire length of
a 1/2WL dipole, using it to "measure" the phase shift
through a loading coil is invalid.

The reason that the total current phasor doesn't have the
same rotational speed as the forward and reflected currents
is that it is the sum of the forward and reflected currents
which are rotating in opposite directions. The two phase angles
add up to almost zero all along a 1/2WL dipole.
--
73, Cecil http://www.w5dxp.com