I have no idea why I didn't test things at the antenna but chalk it up to
new born twins....
Here are the 80M results:
3.770Mhz 3.789MHz 3.826Mhz
42 ohm impedance 42 ohm impedance 55 ohm impedance
2:1 SWR 1.4 SWR 2.0 SWR
Bandwidth at 2:1 is only 56 Khz. Manual states 100Khz at 2:1 Had 30Khz more
bandwidth in the shack. Coax feedline was making a difference here.
Take the radials off and Boom!
3.870Mhz 3.883Mhz 3.910Mhz
80 ohm impedance 80 ohm impedance 85 ohm impedance
2.0 SWR 1.6 SWR 2.0 SWR
40 Khz of bandwidth.........? I thought it would go higher with a less
efficient antenna. A 94Khz jump in resonant point.
THE 40M results:
7.132Mhz 9.972Mhz 6.846Mhz
80 ohm impedance 50 ohm impedance 48 ohm impedance
2.0 SWR 1.2 SWR 2.0 SWR
286Khz bandwidth as advertised, or close enough. Resonant point slightly
lower by 10Khz than measured in shack.
40M Results with No Radials-
7.213Mhz 7.286MHz 7.392Mhz
impedance 60 ohms impedance 70 ohms impedance 90 ohms
2.0 SWR 1.6 SWR 2.0 SWR
Conclusion: I still have a 8-10 ohm difference in impedance when comparing
40 meters to 80 meters at the feed point with or without radials attached.
So it is the antenna. I had a suggestion emailed to me that it is because
the 80M antenna portion is a 1/4 design and the 40M antenna is a 1/2 wave
design. This would explain the size of the 40M coil considering the antenna
itself is almost a quarter wave in length for 40 meters.
Also, it goes to show the huge difference even a small radial field can
make. I use very heavy insulated hard copper wire but if you saw my puny back
yard, you would wonder why I am even trying a low band array.
Any input on these numbers is appreciated except by SWR critics. This all
about impedance and the effect it can have in an array. If this was just a
stand alone antenna, I would not be putting the effort in. Also, I don't plan
to operate below 7.000Mhz. I was using an analyzer. I just can't wait for
those questions.
Thank you= And thank you to those with some excellent suggestions-
73
Paul N0AH
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