> It says that adding radials may make the radiation
> resistance below 50 ohms.
> On page 10 it says that enhancing the radiation can be
> done by adding
> radials. Cushcraft says 16 radials 50-60 feet will help,
> but will lower the
> radiation resistance requiring a matching network such "a
> shunt inductor,
> fixed-ratio Ununn, transmission line transformer, or
> adjustable L-network."
> What Joe has done with his antenna is doubled the
> "recommended enhancement".
> With an SWR of 2.5 to 3.0 the radiation resistance has
> dropped from 50 ohms
> to 17-20 ohms, so about 30 ohms of ground loss resistance
> has been
> eliminated. This increases the efficiency by about 4 db.
> Remember that the MA160V is only about 24 feet from base
> to the loading coil
> and top loading wires and vertical "stinger" which gives
> about 0.05
> wavelength effective radiator length.
> In summation, I personally believe this antenna will be a
> compromise at any
> power level over any radial system compared to typical 160
> meter antennas in
> use.
I fully agree with George.
Assuming a vertical .05WL (18 degrees) high the maximum
possible current loop radiation resistance for any possible
configuration of loading is 1580 times the height in
factions of a wavelength squared, or 3.95 ohms. Rr = 1580
times square of He That is the very MAXIMUM radiation
resistance possible. It will always be less than that.
With base loading radiation resistance and uniform diameter
element radiation resistance would be 1/4 of that value, or
about 1 ohm.
If you have a simple series-fed 27-foot radiator and no
matching and have a 50 ohm feedpoint resistance and top
loading the very maximum efficiency would be 4/54= .074 or
7.4%. That's the best you could ever expect to do. You have
at least 11dB loss and probably more. There isn't any way
possible around that.
Manufacturers almost always focus on SWR. They do that
because people can easily notice SWR, but most will not
notice 10dB of loss.
SWR sells antennas, but high efficiency makes a good signal.
73 Tom
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