My mini-dissertation strictly applies to Class A [so-called "Clear
Channel"] stations only, who almost universally use single,
omni-directional verticals since they are not required to protect any
other stations at night. There were a few Class A's on the coasts that
did use directional phased arrays since there weren't many/any listeners
out at sea but I don't know if any of them are left. Non-Class A's
generally employ 2 or sometimes 3 phased verticals to achieve
directional patterns at night to protect co-channel stations, putting
null(s) in the direction of their service areas.
Class A's, such as KFI, seek to maximize the coverage in their service
area [i.e. maximize the area covered with an adequate field strength].
Neither a 90-degree vertical ... current max at the bottom ... nor a
180-degree ... current max half way up the tower ... will do that. At
640 KHz, a half-wave is ~730 ft.
The obsession with VSWR in ham radio is a bit surprising. I can't
really remember when the term became common, or when I first saw a VSWR
bridge, but I do know that I never saw one in SE Asia in the mid-60's.
These days, high VSWR seems to equate to "antenna that doesn't work."
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 12/18/2018 12:38 PM, hawley, charles j jr wrote:
Interesting, I had an analog computer course exercise at the U of I Urbana when
we had two verticals separated and phased to define the coverage pattern. I
don’t remember the length of them. It’d be interesting to recall what it was.
Chuck
KE9UW
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