Using a 4:1 Balun gets you nowhere near 50 ohms if you're coming from 450ohm
ladderline (which is not specified in the oroginal post), it gets you closer
to 110ohms. What you need is a 9:1 balun to take 450 ohm line to 50 ohms.
However, if your only RF issue is with the keyboard, you may be better off
putting a choke on the USB cable to the keyboard rather than trying to track
down the problem by changing feedlines and baluns. There's lots of
information online about RFI mitigation using ferrite online..
73 de Al, KE1FO
Visit my amateur radio contesting blog at ke1fo.wordpress.com.
On Wed, Jul 2, 2008 at 1:36 PM, Richards <firstname.lastname@example.org> wrote:
> I believe the use of nonresident feed line is a common consideration.
> Apple with the dipole, I am thinking that your ground system is a good
> but maybe not fully necessary, as the antenna is fully balanced.
> Why not use a 4:1 balun, to bring the 450 ohms on the window line
> down to 50 ohms, or thereabouts? In outboard tuners, there is
> usually a 4:1 balun, not a 1:1 balun, for open feed line, so I am
> curious about your choice of that ratio.
> Thanks in advance
> Happy trails and 73. ---- Richards - K8JHR ----
> w4lde wrote:
> > The 1:1 current balum used to convert the 450 ohm balance line is
> > external to the tuner, use about two feet of coax from the balum to the
> > tuner.
> > One article recommended odd multiples of a wave length is desirable at
> > the lowest operating frequency while other articles don't address this.
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