|[AMRadio] RE: new antenna and matchbox a bust.|
brett.gazdzinski at verizonbusiness.com
Wed Jan 31 08:59:52 EST 2007
I expect you are 100% correct.
In the end, I cut 40 inches off each end of the
antenna so it would go tight, and I cut about 7 feet
off the open wire line.
It now ends at the top of the house, where the coax starts.
That gives 80 feet each side roughly, and I don't arc the tuner
on high power. Better but not perfect...
I am not sure if the swr is a problem as it is now, there
is very little coax in the picture, but I could add loading
coils 3/4 of the way out each leg, or at 33 feet at the
40 meter points....just some B+W coil stock over an insulator.
> With your open wire feeders and dipole, 50ft + 40 ft = 90 ft.
> total length
> for each leg of the dipole + feeders. 30ft is approximately
> 1/8 wavelength
> at 75m. so the total length is ~3/8 wavelength. An odd number of
> wavelengths is about the worst possible length to choose for
> a resonant
> feeder system, since it is midway between a current loop and
> a voltage loop
> at the input end of the dipole/resonant feeder. That is the
> most highly
> reactive length you can possibly achieve, and very difficult
> to tune, and
> oddball things like the ant tuner capacitor arcing over even
> at low power,
> low efficiency, impossibility to get low SWR, etc. Add about
> 30 more feet
> of open wire line, and the total length will be 120 ft. (a half
> wavelength), and the end of the feedline where it attaches to
> the tuner will
> be high-Z @ low reactance. It should feed very well with
> parallel tuned
> circuit configuration at the tuner.
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