[Elecraft] KPA1500 RFI on 12m

[Bob McGraw K4TAX]

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
>
>