Bill Aycock wrote:
> As far as the subject of 1/2 wave verticals goes, the WWV site leaves
> out a LOT!
> 1. Where is the feed point?
The upper 1/4 wave of the 1/2 wave monopole is insulated. The antenna is
fed with coax at this point against the skirt wires. This is described
in the QST article and can be scene in the picture link of the WWVH
antenna that W4TV posted.
> 2. what is the feed point impedance?
The article says 50 ohms.
> 3. Are the lower ends of the "guys" grounded?
No, the article indicates they are insulated
> 4. Why is it important that the Coax feeds do not cross?
Makes for a neat installation, but I can't imagine that it makes any
difference to performance whatsoever.
> Does anyone know?
> Are the arrangements of the TTers with 1/2 wave verticals like WWV,
> and if not, why reference it?
Probably not exactly, Bill. I thought the point in the article QST where
they mentioned the ground radials not impacting feedpoint impedance
somewhat paralleled N3OX's experience. The article also mentions the
expected gain over a 1/4 wave monopole (1.7dB).
One interesting thing is that per the picture link that W4TV posted,
they elected to use ground radials in the WWVH installation, but they
did not in the WWV installation (the QST article claims that when it was
determined tha the radials didn't effect input impedance it was decided
not to include them in the installation). Perhaps radials were added
later at WWV (my understanding is that they were only included for the
two backup broadband monopoles antennas). I would be interested if
anyone can confirm this. This speaks to previous discussions as to what
field strength benefit is derived by including radials under a 1/2 wave
vertical dipole.
73, Mike W4EF...........................
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|