[BC] Too Tall towers....

[Cowboy]

On Monday 18 July 2005 19:23, Phil Alexander wrote:
> On 18 Jul 2005 at 16:39, Dan Strassberg wrote:

> > 2. Is there a practical way to electrically shorten such a radiator? For
> > example, can you attach a skirt to the bottom and drive it so that the
> > skirted section (in this case something between about 40 degrees and 100
> > degrees) does not radiate?
> 
> The NAB Eng HB suggest possibilities including skirting and isolation
> of the upper part.

 Basicly, turn it into the J-pole discussed in the Zepp thread.
 It should be possible, but I know of none actually done that way.

> > I've been trying for several years now to find someone who can comment on
> > electrically shortening AM towers that are too tall for a diplexed station
> > operating at a frequency higher than that of the station that originally
> > occupied the tower.

 /snip/

> Theory says it can be done, but it seldom happens so there is not much
> literature. Secondly, each tower will have its own dimensional peculiarities.
> The best way would be a modeling exercise in NEC-4 to look at possibilities
> before the field work. However, it is possible.

 Agreed, and I don't think it would be all that difficult.

On Monday 18 July 2005 23:37, Clive Warner wrote:
> >2. Is there a practical way to electrically shorten such a radiator? For
> >example, can you attach a skirt to the bottom and drive it so that the
> >skirted section (in this case something between about 40 degrees and 100
> >degrees) does not radiate?

> The correct method is to call in a competent steelwork contractor who will
> separate and jack up the top part of the structure enough to install an
> insulator at the optimum desired electrical height.
> - Clive

 That's certainly one way, but since he mentions a diplex, methinks electricly
 isolating the top section at the higher frequency with a proper skirt would be
 "better".
 Sectioning the tower will certainly work for the higher freq station, but comes
 with other problems. ( cost, mostly. Whether or not the stick can support
 a diplexing filter at the section point, stuff like that )

 Probably, sectioning the stick would have less long-term maintenence issues.