Jim Lux wrote:
>>> I assume that Dan's AutoEZ model calculates the mutual impedances, although
>>> it's not clear from the QRZ article.
Yeah, I kinda glossed over that. The model does not "calculate" the
mutual impedances directly but the mutual coupling is taken into
account.
The model is first configured with two separate "current" sources, one
at the base of each element, with no L or C loading on the elements
and with no half-wave transmission line. The two sources are:
Src1: 1.0000A at 0°
Src2: 0.9602A at -94.98°
Because of the mutual coupling between the two elements the Z values
at the sources are:
Zin1: 24.03-j17.01
Zin2: 54.82+j21.19
That's what is shown in the 4th image. Then the model does the
calculations using the formulas shown in the 3rd image to find the
"jA" and "jB" reactance values and hence the L and C "detuning"
component values that will (theoretically) produce the desired
results.
The model is then reconfigured to have only a single source, plus the
two "detuning" loads on the elements, plus the half-wave transmission
line. If the line is an exact half-wave (only at one frequency) and
has zero loss the *actual* currents at the base of the elements will
have the desired magnitude and phase relationship.
Now scroll down to "With all of that done ..." and see the image just
below that. The model extracts and reports the *actual* element base
currents with the OV feed system in place. The ratio of the
magnitudes is 0.9296 (not the intended 0.9602) and the phase
difference is -96.63 (not the intended -94.98).
So the model just makes it easy to do some otherwise tedious
calculations and then makes it convenient to see the results as
extracted from the NEC output file via EZNEC.
Dan, AC6LA
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|