"Dave Shrader" wrote in message
news:hBdPb.92880$nt4.225549@attbi_s51...
Cecil Moore wrote:

Craig Buck wrote:

I was talking about radiation efficiency taking into account the ground
losses. The ARRL Antenna Book equation is Efficiency = Radiation
Resistance
divided by the sum of Radiation Resistance + Ground loss + Coil loss.
Plug
in a 6 ohm ground loss and whatever you want to assume for the coil
loss.
The higher the radiation resistance the higher the efficiency. No?


For an 8 ft center-loaded whip on 75m, the ARRL Antenna Book gives 0.8
ohms
as the radiation resistance and 22 ohms as the feedpoint impedance.
That's
an efficiency of about 3.6%, about 4 watts radiated for 100 watts input.

Keeping Ground Loss and Coil Loss constant and increasing the radiation
resistance from 0.8 ohms to 1.6 ohms changes the efficiency to 7%. Hmmm
... the higher the radiation resistance the higher the efficiency!!

In all the cases I reported the antennas were on the same ball on the same
truck: ground losses were a constant.
They were all of comparable length, the Hustler a bit shorter than the
screwdriver, the bugcatcher a bit longer, but comparable radiation
resistances; about an ohm.
The lower the loss resistance the higher the efficiency, which gets back to
the ~10 ohms of the screwdriver;
Comparing that to the ~20 ohms of the Hustler and bugcatcher leads me to
suspect the difference is in the loss resistance which is consistent with
observed performance on the air.
With my 200 watt mobile rig I should radiate about 16 watts on 80!
;^)
73
H.
NQ5H