I also disagree. AM broadcast verticals are designed to achieve a
desired pattern and main lobe elevation angle. Over flat ground, 225
degrees will optimize the ground wave coverage. However, higher powered
stations will then suffer from self-interference at the coverage edges
because the sky wave and ground wave interfere. It's common to shorten
the antenna a bit to perhaps 195 degrees or so which tends to reduce the
self-interference. Once the pattern and main lobe angle have been
defined, the feed point is matched to the transmission line with an
appropriate network. Neither 225 degrees [5/8 wave] nor 195 degrees are
resonant lengths and both require a matching network.
Many hams do not have the luxury of resonant antennas on every band. It
seems perfectly reasonable to employ some sort of matching network to
match the feed point to the coax on bands where it is not resonant
AND/OR does not present a 50 ohm load to the coax and needing to do so
does not imply there's something wrong with the antenna.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 3/31/2019 9:44 AM, W2xj wrote:
I would disagree. Most high power commercial operations use non-resonant
mismatched antennas. Typically there is either a tuner at the antenna or open
wire is used.
Sent from my iPad
On Mar 31, 2019, at 12:13 PM, Ken G Kopp <[email protected]> wrote:
If an antenna is showing a VSVR of 3:1, something about the situation
is wrong, and most likely it's -not- the antenna. Fix the problem … feed
the antenna power where it's resonant, assuming the antenna is actually
resonant on the amateur band of interest. Expecting a tuner to compensate
for a problem external to an antenna is unreasonable, IMO
73!
Ken - K0PP
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