Topband: Shunt-fed tower vs. T-vertical

[Herb Schoenbohm]

Julius Fazekas wrote:
> What distance from the tower is a good rule of thumb for the cage wires?
>
> Three is the minimum, would four be "better", as in easier to match, provide better isolation?
>
> Pondering this for a 48' mast for 80M, as I don't think I have enough on top to make it useful on 160...
>
>   

A 48 foot pole on 160 without any top loading will result in low feed 
point impedence and low efficiency even with a good silver plated 
loading coil. It still may be better for DX than a low dipole.  The cage 
helps as well and 36" to 48" are fine...and 4 wires are slightly better 
than three but not much.  A 48' tower, appears short, but, with some top 
loading like a tri-bander on top you will notice that such a radiator is 
clearly better than a low dipole or inverted "L" in laying out a lower 
angle DX signal on TX.  Remember the tower need not resonate on 1.8.  As 
with many short 60 degree BC station tower installations, so much 
depends on the ground system and the quality of ATU components.  The 
cage can only help making the match easier to achieve to a certian 
degree.  If you don't have a beam on top of your tower consider 
constructing a 30 foot stinger out of graduating sections of aluminum 
tubing or create some top loading by connecting in about 30 per cent of 
your top guy wires if possible as long as the downward angle is not to 
acute and is around 45 degree declivity or better.

73,

Herb Schoenbohm, KV4FZ