On 1/16/2012 8:34 AM, Peter Voelpel wrote:
> TLDetails calculates additional 0.77db loss with 150 Ohm at the feed point
> and 0.8db at 16.67 Ohm with your example.
My example was for a 1.5:1 SWR. A 150 ohm or 16.67 ohm load is NOT 1.5:1
with 50 ohm cable.
Yes, the loss due to mismatch will be greater with the greater SWR, and
it's a big part of why I use Belden 8213 (foam RG11 with a big center
conductor and a robust copper shield) to feed my 80/40 fan dipoles that
are up about 32 meters. The use of 75 ohm coax provides a better match
to those high dipoles than 50 ohm, which establishes a lower SWR on the
line both at the band edges. It also minimizes losses when I'm loading
those antennas on 30M, 17M, 15M, 12M, and even 6M, and they work quite
well on those bands.
I've confirmed the correctness of the curves plotted in the ARRL
Handbook with some spot calculations using the fundamental transmission
line equations. So has Steve Stearns, K6OIK, a communications engineer
at Northrop Grumman. You'll also find good agreement with N6BV's TLW
software, included on the disc that comes with the ARRL Antenna Book.
73, Jim Brown K9YC
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