>"The executive summary is that 1) being close to a drop-off can provide a LOT
>of gain in the direction of the drop-off and that antennas don't need to be
>high; and
2) that terrain in any direction can strongly influence optimum height for
antennas for each band."
About 15 years ago, Bill, W4ZV, presented a case study of Frank Lucas' QTH.
W3CRA was located on the north side of a geological knob in Canonsburg, PA,
just below the top ridge. Notice the extreme gain achieved at super low
arrival angles when sited on the lower edge of a moderately sloping hill. Also
notice that the statistical mode from PA into deep Asia is only 2 degrees above
the horizon.
http://users.vnet.net/btippett/w3cra.htm
About two years ago, I ran the same analysis but used the actual geographical
coordinates of Frank's tower. Amazingly, the tower -- and what's left of a 3
element Yagi can still be seen today on Google Earth:
40.244897 NLAT
80.181486 WLON
I took the coordinates and ran it through K6TU's automated profile generator,
then imported the data into HFTA. Doing so allows for some interesting "what
if" analysis. Like, what if Frank increased or lowered antenna height on his
70 ft. self-supporting tower by only a few feet? I ran such a model and found
significant changes in low angle gain with small changes in vertical height.
But these same small changes in antenna height are nearly meaningless over flat
terrain. HFTA allows one to compare results over flat terrain, just as W4ZV
shows in the link above.
Paul, W9AC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|