[TowerTalk] Sloper Question

[w8ji.tom]

Hi Eric,

You seem to be saying by choosing the proper attachment point, the tower
radiates and the sloper does not. 

Since the sloper has to carry exactly the same common mode current as the
tower, perhaps you can explain exactly what prevents the sloper from
radiating?

I also understood you to say feedpoint impedance is secondary to finding
this "sweet spot" on the tower.
I think most people have no idea what the pattern is, and are mostly
concerned with SWR.  SWR is a function of the self-impedance of the tower
at the point where the sloper is attached, since the tower is the other
half of the feedline termination. The feedline "pushes" against both the
tower and sloper.

> A bit of modeling of the tower system and the proposed sloper
> will quickly reveal a reasonable attachment point (if one indeed
> exists... and it usually does) which will produce an effective
> antenna system.

Slopers indeed can be planned, but:  

1.) Most people expect an out-of-box 1/4 wl sloper to work by just
grounding the shield of the cable to the tower.
  
2.) If they model the system, they need to model ALL the elements (and
boom) of any antennas attached to the tower, as well as all uninsulated or
poorly "detuned" guy lines.

3.) If they are successful in modeling the tower and all attachments on the
tower properly, and if they look for a "sweet spot" that has a low
self-impedance at the operating frequency of the sloper, it can be up to
1/4 wl away from the poorest points. In some cases, there might not even be
a "sweet spot" without adding counterpoises.

73 Tom


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