ARRL literature has consistently underestimated the losses of
ladderline. For example, the matched losses quoted in the ARRL Antenna
Book - at least up to the 21st edition - are about one half the figure
you arrive at from a basic analysis of the copper losses.
The QST article "The lure of ladderline" also grossly underestimates the
ladderline losses. At 3.8MHz a 66ft dipole at a height of 30ft over
average ground has a feedpoint impedance of around 11-j964 Ohms; that
would produce a loss of 8.9dB in 50ft of Wireman 551 ladderline or 6.1dB
in the superior 554, compared with 1.37dB quoted in the article. Even
600 Ohm open-wire line would have a loss of over 2dB with that load.
Don't get me wrong, I like balanced transmission lines; but be very wary
about any of the loss figures quoted by ARRL.
If you do the basic maths on the copper losses, you'll arrive at a
matched loss figure almost exactly twice the ARRL figure. Call me
cynical but: did ARRL forget that there are two conductors and failed to
multiply by two?
Steve G3TXQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|