[TowerTalk] SteppIR 40/30

[Jim Lux]

At 04:17 PM 11/4/2003 -0500, Mel Martin wrote:
>I'm not sure that's necessary... they could use a Hi-Q loading coil... this
>would work well since bandwith isn't the issue it is with a more
>conventional shortened 40... it wouldn't have to be much bigger than a 20
>meter antenna...

The tricky thing with a shortened element and a loading coil is the 
increased losses. Not so much in the coil, but because the short element 
will have a lower radiation resistance, so resistive loss will be a larger 
fraction of the total load impedance. The reactive power circulating 
between coil and capacitive antenna will also lead to more IR losses. On 
the other hand, it IS a multi-element array, so maybe it all comes out in 
the wash... The full size element array would have some amount of reactive 
currents circulating just to excite the passive elements.

Taken to an extreme, it starts to look like a compact loop antenna, where 
the capacitor which tunes out the reactive component is essentially 
lossless, but the resistance of the element is very significant compared to 
the milliohm Rr of the loop.

However, a half length element (as in using a 20m element on 40m) is still 
going to have a fairly decent radiation resistance (roughly 1/4 that for 
the full size element).  The gain will also be slightly less, because the 
short dipole has a pattern that is more isotropic than the 2.15dBi dipole 
upon which the standard beam is based.

Jim, W6RMK