[RFI] Auto quieting

Jim Brown jim at audiosystemsgroup.com
Sat Oct 10 03:15:36 EDT 2015

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.

In a tutorial workshop I led for audio and video pros in 2005 in 
Chicago, I demonstrated a setup comparing microphones running on 
shielded twisted pair (the standard for audio) and on one pair of CAT5, 
with another pair of the CAT5 cable providing a ground for the 
microphone's shield. I excited that setup with a 5W 2M, 220MHZ, 440 MHz 
talkie and and a TDMA cellphone on 900 MHz that is notorious for RFI. 
Both setups provided very good immunity, with slight RF sensitivity at 
some frequencies, and there was NO advantage to the shielded cable.

By contrast, zip cord, even the "glorified" stuff sold by the audiophool 
companies, is TERRIBLE for RFI. I got more than a few sexual favors from 
sweet young things (this was a LONG time ago) curing RFI in downtown 
Chicago highrises replacing zip cord with twisted pair for speaker wiring.

Tongue firmly in cheek, but not lying. :)

73, Jim K9YC

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