[AMRadio] RE: new antenna and matchbox a bust.


Brett gazdzinski 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.

Brett
N2DTS



  
> 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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