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W5DXP > ANTENN 20.05.05 21:36l 32 Lines 1277 Bytes #999 (0) @ WW
BID : 4286722D$1_2
Read: GUEST
Subj: Re: High Impedance Feedlines = Lower Loss - Why ?
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<DK0WUE<7M3TJZ<SV1CMG<LU1KBK<LU4EGV<
LU4EGV<G8LMC
Sent: 050515/0807Z @:G8LMC.AMPR.ORG HamServ V2.66
Reg Edwards wrote:
> The number one reason for attenuation being higher is because the
> conductor diameter is smaller and, as a consequence, its resistance is
> higher.
On that we can disagree. The *number one* reason for attenuation
being higher is because, in a matched feedline, the losses are
proportional to the square of the current, and the current is
inversely proportional to the characteristic impedance of the
feedline, i.e. given #20 wire, a Zo-matched 75 ohm feedline
will have Sqrt(600/75) times the I^2*R losses of a matched 75
ohm feedline. Proof:
SQRT(100w/75) = SQRT(600/75)*SQRT(100w/600)
SQRT(100w/75)/SQRT(600/75) = SQRT(100w/600)
100w/600 = 100w/600
Given that the center conductor of RG-213 is the same size wire as
a parallel feedline, a *very* large percentage of the difference
in matched line dissipation is due to the Z0. (I don't know the
size of the center wire in RG-213 but it looks like #14 or #12.)
I don't think the RG-213 center conductor is at all smaller.
--
73, Cecil http://www.qsl.net/w5dxp
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