[Elecraft] Baluns and 450 ohm line

[kc4kgu@ENTERZONE.NET]

On Mon, 3 Jun 2002, Stuart Rohre wrote:

> Don is right that with multiband doublet use, the feeder may, at the
> transceiver, present various impedances.  Thus, the use of parallel high
> impedance lines, Ie the 300 and 450 and 600 ohm lines is attractive, as they
> are lower loss at the mismatch SWRs which would present unacceptable losses
> in Coax.  In fact, on the lowest band of the doublet where it may be exactly
> a half wave at some frequency, its center would be closer to 72 ohms
> feedpoint than to the line impedance, as long as the transmatch can adjust
> for the combination of feeder, balun, etc., you are in good shape.  The 1:1
> balun may work better for cases where your line ends up being closer to 100
> ohms at the transmatch.

I'm just currious about something here that perhaps (almost
certainly) someone on the list can enlighten me on.  I currently feed my
75m doublet with twin pieces of RG8X.  This presents a line impedence of
about 100 ohms.  Prior to feeding with twin pieces of coax, I cut the
doublet for resonance at 3.875Mhz.  It showed a 1:1 match at 50 Ohms
according to the MFJ-269 analyzer.

Now, since the MFJ-269 is designed to give readings based on 50Ohms, what
should I be looking for when I check one of my antennas that is being fed
with twin coax with a 100 Ohm feedline impedence?

73 de John - KC4KGU
K2/100 #2490