[Elecraft] KXPA100 Mobile Operations -- Power Output

[Jim Brown]

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