[Lowfer] TMO back on

[Lyle Koehler]

The vertical has a null straight up, while the loop has nulls at right
angles to the plane of the loop. They both have figure-8 radiation patterns,
except that the pattern of a vertical is sliced in half by the ground plane,
and they both have directive "gain".

If you use the classic formula for the radiation resistance of a single-turn
loop in free space:

Rr = 31,200 * (area squared) / (wavelength raised to the 4th power)

and want to calculate the effective radiated power using P = (current
squared) * resistance, you have to add 3 dB to the result because all of the
radiation is confined to one hemisphere. This correction does not apply to a
ground-mounted vertical, since it has already been taken into account in the
formulas for radiation resistance. For example, the calculated radiation
resistance of a 15 meter square loop at 185 kHz is 0.000228 ohms. In free
space the effective radiated power with 1.5 amps of current would be 0.51
milliwatts, but in the presence of the earth the ERP is 1.02 milliwatts (at
the pattern maxima). To put that in perspective, antenna modeling software
predicts a radiation resistance of 0.061 ohms for my LEK vertical at 185
kHz, and with a current of 200 mA, the ERP would be 2.24 milliwatts. In this
case, though, the radiation is the same at all azimuth angles.

Lyle, K0LR