No subject

[hkennedy@ix.netcom.com]

Well, in summary, Ive received a lot of mail indicating everything from the
vertical ends don't matter much (minority opinion) to the fact that they
matter a lot but there is not much you can do about them, in a practical sense.

There was one mention of 'shielded downleads,' there were two suggestions
that it is impossible to shield the downleads.  Most seem to agree that
because sloping ends have the same vertical drop as straight-down verticals
ends, they therefore accomplish nothing other than perhaps some mechanical
advantage in being able to tension the system, and catch the occasional deer.

Anyway, here is my idea, and it is possibly redundant with a mention of un
uns on the ends of transmission lines...

For the vertical drops, use coax, configured as a true transmission line.
For the beverage's terminated end, at the ground end of the coax drop, tie
the shield to the ground post, and the center conductor through a resistor
to the ground post.  For 50 ohm coax, use a 50 ohm resistor.  The ground end
is now properly terminated, and the coax will be a transmission line, not a 
radiating wire -- yes?  At the top end, the coax shield floats, and the end
of the beverage wire hooks to the coax center conductor through a resistor
50 ohms less than you would have used, as it will be 'terminating' into a 50
ohm load.  Better still would be a 9:1 transformer at the top of the coax,
transforming the 50 ohm transmission line impedance into the characteristic
impedance the wire would like to see for best front to back.
 
If this seems reasonable -- Ill describe the driven end, which is a little
more obtuse!

73

Hal, N4GG


--
FAQ on WWW:               http://www.contesting.com/FAQ/topband
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com