On 1/23/13 12:41 AM, Hal Murray wrote:
mspencer12...@yahoo.ca said:
This URL goes into some of the issues involved in using 75 ohm coax in a gps
system. I do acknowledge that several GPS manufacturers have promoted the
use of 75 ohm coax so some of the conclusions might be arguable..
If the coax is short, the loss due to mismatch dominates. If the coax is
long, the attenuation per X meters will dominate.
And it's not clear that there's actually "loss" due to mismatch. Most
antennas/preamps/receivers don't have exactly 50 ohm impedances. 75/50
is only 1.5:1, and there's an awful lot of antennas and receivers out
there that only claim 2:1 VSWR. The usual spec for the antenna is
1.5:1, so for all you know the Antenna and Receiver is already 75 ohms,
and RG6 will give you a better match than 50 ohm LMR400.
probably a bigger issue *might* be that reflections will create
synthetic multipath from the signal reflecting back and forth in the cable.
There should be a crossover length What is it for 50 ohm RG-58 and 75 ohm
RG-6?
If you are designing your own antenna, you have the option of making one that
matches 75 ohm rather than 50.
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