Total posts : 45366
[quote=Neil (radio8Z)]Rich’s numbers indicate some difference …[/quote]Hi Neil – It is all a matter of definition, I guess, but the 3-meter vertical radiator system showed about 47 % more field with that 4-spoke top hat than without it. Other things equal, the power applied to the 3-meter vertical system without that top hat would have to be increased by 2.16 X (to 173 mW) in order to produce the same field at a given location that 80 mW did using the top-hat version.
That 2.16 X improvement in radiated power would extend the distance to a given, usable groundwave field strength contour by about 23%. Some might find that to be useful.
While discussing my earlier post here, I should re-state something I wrote in it. I said that the performance of configuration 3 was not as good as # 1 because # 3 was shorter. Looking at the NEC data and thinking about this some more, I realized that the reason for this is that the radiation resistance of # 3 is less than # 1, and therefore a greater percentage of the available power is dissipated in system losses.
[quote]By the way, has anyone heard of a “Slinky” antenna? [/quote]The basic belief about these types of antennas is that the electrical length of a radiator can be extended by using a spiral conductor over a short(er) linear dimension. Modeling them would be a chore, but my intuition for practical Part 15 use is that the “OD” of the slinky would tend to reduce the reactance compared to a straight, small OD conductor of the same linear aperture dimension, but that its system radiation efficiency would be little different. This would be similar in effect to using a large OD pipe instead of a small OD pipe or wire.
//
