[RFI] Auto quieting
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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