On 10/12/2015 2:15 AM, Roger (K8RI) wrote:
On 10/10/2015 3:15 AM, Jim Brown wrote:
On Fri,10/9/2015 10:31 PM, Roger (K8RI) wrote:
I fail to see where two runs of RG8 size cables in a car, large SUV,
or long cab pickup truck would be cost prohibitive.
But it's wasted dollars. Most RF guys fail to realize the noise and
RF rejection inherent in good twisted pair. For more than a century,
telco went cross country on unshielded twisted pair running next to
power lines. CAT5/6/7 is four high quality, 100 ohm twisted pairs,
each with a different twist ratio to further minimize crosstalk
between pairs.
War story.
Some years ago, I had to verify the performance of a GPS timing pulse
buffer design over a range of temperatures and supply voltage. This
signal was a relatively high amplitude, short, fast, unipotential pulse
carried on a 50 Ohm twisted pair. The complete equipment was being
automatically tested in another lab, who, not having 50 Ohm STP, used
Cat 5 instead. This didn't work until I showed them they could use two
Cat 5 pairs of the same length in parallel.
I would later have to deal with an angry customer engineer, who'd
thought one measured the signal on 50 Ohm twisted pair by using a 50 Ohm
setting or terminator at the scope, and isolated the scope from the
twisted pair by using a 10 MOhm 10:1 scope probe connected "upside
down" WRT to the pulse.
I talked to his tech, and didn't hear from him again.
Cortland
KA5S
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