[TowerTalk] Re: Xfmr.

[n4kg@juno.com]

Series Transmission Line Transformer Matching -  N4KG

One way to determine the electrical length of a feedline is
to determine the LOWEST frequency at which it represents
1/4 WL (look for near-zero impedance with END OPEN) or
1/2 WL (look for near-zero impedance with END SHORTED).

Before the new analyzers became available, I used to do this
with an old HP-606 signal generator and RF millivoltmeter.
(A diode detector to a small capacitor and high impedance
DC voltmeter might also work).

By "reversal" on long 10M runs, I mean that the percentage
frequency shift (Delta F / Fo ~ 0.02) times the number of WL 
of cable (12 WL = 420 ft X 0.8 VF= 336 ft) = 1/4 WL.  

SO,  if you have a multiple of 1/2 WL on CW, you will 
see the antenna Z (50 ohms) at the end of of the feedline,
BUT, when you go to SSB, the antenna Z (say 50 ohms)
will be transformed to 112 Ohms because the line looks
like it is 1/4 WL longer on SSB than on CW due to the
frequency shift.  (560 KHz of shift represents 2% per WL 
of transmission line on 10M.)

de  Tom  N4KG

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