Steve,
Comments inserted below:
K7LXC@aol.com wrote:
>
> In a message dated 3/20/02 5:37:37 PM Pacific Standard Time,
> n8de@thepoint.net writes:
>
> > When you raised the antenna to 80', did you measure the resonant
> > frequency AT THE ANTENNA? .. or at the end of a piece of coax?
> > The ONLY way to 'get it right' is to do ALL measurements AT the antenna,
> > NOT down at the shack!
>
> Well, you can measure all you want at the antenna but the only place
> where it MATTERS is at the end of the coax and what the transmitter 'sees'.
That's true, IF you're only interested in what impedance the rig/amp
sees! If the resonant frequency of the ANTENNA, and NOT the SYSTEM of
antenna/feedline is of ANY interest, the measurement MUST be made AT THE
FEEDPOINT [capitals to ME mean EMPHASIS, NOT SHOUTING!].
> Some antennas are wacky at the feedpoint but FB in the shack (I'm sure the
> feedline loss has a little to do with it). As long as the radio's happy - so
> am I.
My statement above covers this!
>
> I don't know why your antenna didn't change resonance when you got it up
> in the air. The 13.650 resonance on the sawhorses is about right. Sounds like
> you've got some interaction somewhere - guy wires? Wire antennas?
>
> You only need to get it 30 feet or so off the ground to minimize ground
> capacitance effects.
Thirty feet? .. for 20m? That's not even 1/4 wavelength, and hardly a
good place to measure .. besides, the feedpoint of the 205CA is NOT near
the mast, so would require some real gymnastics effort to get to it for
true resonance measurements.
>
> I seem to recall in the dark, distant past that someone said that
> computer modeling had changed the dimensions to make the antenna play better
> so maybe you don't have the newest dimensions. I think they used to be on the
> old Hy-Gain/TELEX website.
The 205CA dimensions are in the ARRL Antenna Handbook and are also
online, but have misplaced the URL.
Don - N8DE
>
> Cheers,
> Steve K7LXC
> Tower Tech -
> Professional ham radio tower work
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