On 1/12/2014 11:49 AM, Phil Hystad wrote:
Jim,
Thanks for the suggestions on reducing noise. I can put common mode chokes (at
least I think I can) on my DC wiring but I cannot effectively put in twisted
pair unless I take out what exists now and replace it with twisted pair.
Therefore, hoping not to have to do that I ask the following question.
Question: How much difference will the twisted pair have in reducing noise
versus having common mode chokes only?
Twisting strongly rejects differential-mode coupling of the noise --
that is, the RF trash that appears between DC+ and DC-. There are two
reasons why that matters. First, electronic systems in many vehicles are
susceptible to RF, are poorly filtered on both DC and signal wiring, and
misbehave when they pick up RF. The systems in my Toyota big SUV went
into "limp home" mode with 50 watts on 20M. To get running, I had to
remove the battery terminals from the vehicle so that the computers
would reboot.
The second way in which differential mode hurts us is if any of the gear
on that DC is poorly filtered on its DC leads. That would let noise into
our rigs.
Currently with my Icom 706 the noise due to ignition and other sources is
pretty high but the noise blanker does real good and getting it down to
acceptable levels though not dead quiet as the case if the engine is off.
Noise blankers are fine -- UNTIL a big signal outside of the RX bandpass
pulses them. Then they're useless. The dual-mode blanker in the K3 is
much better than most. I haven't used the KX3 enough to know -- I don't
own one yet -- but I suspect it's pretty good
I have a 2004 Chevy HD2500 (3/4 ton) crew cab pickup truck. The Hi-Q antenna
is mounted on the rear (driver's side) on top of the side panel with my own
custom made mount. I have ground straps at a number of locations and ground
for the Hi-Q is very good (bolted to the frame itself after cleaning the frame
for good contacts. The frame is also grounded to the under side of the body
where I have cleaned off attach points to achieve good ground contact
All that frame bonding is critically important for making the antenna
work (by providing a counterpoise for the antenna), and it MIGHT help
with RF suppression. Caps added for emphasis of key words.
73, Jim K9YC
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