For all interested, you might want to read the relevant article on my
website www.w3fpr.com. It was written directed at QRP ops, but applies
to QRO operations as well.
73,
Don W3FPR
On 10/29/2019 7:56 PM, Bob McGraw K4TAX wrote:
Bill:
Glad to see you post this fact. Hams have had it wrong and doing it
wrong for years, because someone said so. Many hams seem to have less
than zero knowledge on the topic. Oh, less than zero knowledge is
knowledge that is not correct.
Same is true when one uses 450 ohm line, many think they need a 4:1
balun because someone said so. I suppose they believe the "4" in 450
ohm line and the "4" in the 4:1 balun ration have something in
common. Another less than zero knowledge condition.
The electrical length of the wire determines the resonant frequency. Of
course the diameter of the wire contributes to the K factor and bare
wire is different than insulated wire. Thus those two facts must be
considered when cutting an antenna length. Height above ground {not
necessarily earth because of ground conductivity} determines the feed
point impedance.
Ohhhhh there is so much to learn about antennas.
73
Bob, K4TAX
On 10/27/2019 9:23 PM, K8TE wrote:
Most hams cut their antenna length for lowest VSWR which is often NOT the
resonant point. Resonance occurs when XsubL equals XsubC. That means
there
is no reactance at one frequency. Impedance varies greatly with height
above ground. The greatest radiation occurs at resonance which,
again, is
often not at the lowest VSWR. This is why a good antenna analyzer that
displays both VSWR and reactance is so helpful.
Web sites abound with advice to cut the antenna for lowest VSWR. Like
politics, the truth is difficult to find and, apparently, often hard to
believe. And, anecdotal statements about how an antenna works
(WORK--WithOut Real Knowledge--K0BG) often has little to do with its
comparative performance. Too few of us use real data (like WSPRLite) to
compare antennas and arrive at conclusions based on comparative data.
I liked the Pacificon theme this year: "The Science of Radio" That
didn't
always apply in some of the presentations, but fortunately did in most I
attended.
73, Bill, K8TE
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