Indeed. AM broadcast vertical antennas are rarely 90 or 180 degrees,
especially if they are a Class A station. I think both KFI and KNX in
Los Angeles have 195 deg verticals. The design goal is to maximize
field strength in the service area, accomplished by adjusting the height
of the current maxima in the antenna element. All resonance means is
that the reactive component of the impedance at the feed point is zero.
A bigger problem for stations at the low end of the band ... KFI is at
640 KHz ... is that the usable bandwidth of the antenna can be less than
the bandwidth of the DSB signal. [:-) Last time I saw KFI's tower from
Interstate 5, it appeared to have a fairly large capacity hat.
Elecraft ATU's [even the KX1 which is necessarily small with a limited
number of L-C selections] seem to handle reactive loads just fine
suggesting [to me at least] that designing an antenna for azimuth and/or
elevation pattern may be more beneficial than achieving resonance in the
desired part of the band.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 12/17/2018 7:45 PM, W2xj wrote:
Coming from the broadcast side, especially AM broadcasting, I never considered
resonance particularly important. Really it’s just the transmitter that cares.
We always put matching at the antenna but in ham radio we usually have tuners
at or in the TX.
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