[Elecraft] Mobile from 117 VAC

[Rick WA6NHC]

My RV has a 3 KW inverter; I've not noted noises from it on any band but 
it was NOT cheap and it has it's own battery supply (not the house 
battery) and the radio has it's own battery supply.  There is no 
physical contact, only proximity.

We're not in disagreement here but we're approaching it from different 
angles (you have the formal training, we both have some experiences).

My rule:  Bond EVERYTHING to the chassis, including chassis elements to 
each other (paint is a pretty good insulator).  While that does have a 
*small* effect on noise (the every wire IS an antenna consideration); 
mostly bonding is to keep the RF (more correctly RFI) out of systems 
where it doesn't belong , including induction and radiation along the 
power cabling; to radiate from the antenna (while power sources are also 
another good place to provide some twist in the cable).  More bonding 
means more energy to the (intended) antenna and higher efficiencies.

When running >QRP the radio bonding can greatly reduce the effects in 
the radio from RFI.  Simply bonding the 200W RF deck in my truck to the 
chassis removed >90% of the RFI (except 40 meters sometimes turns off 
the cruise control).  The control cable and the mic cable each have 
ferrites in place; they weren't enough.  So we will disagree on your 
last point; my experience in that install provides that. It's all within 
7' of the antenna, hard to keep that any cleaner with that level of 
exposure.

The good news is that the newer vehicles have less cabling since wiring 
is replaced with fiber optics.  The bad news is that there is more 
'stuff' in a newer vehicle to generate and be sensitive to RFI.  I'd 
score that as a wash.

73,
Rick nhc


On 10/9/2017 10:06 AM, Jim Brown wrote:
> On 10/9/2017 9:00 AM, Rick WA6NHC wrote:
>> Overall, not a great plan.
>>
>> Using an inverter, you will introduce RF noise, generate heat and 
>> poor regulation,
>
> I've used "good" ones (Samlex "pure sine wave" with FCC Part 15 Class 
> B certification) and they ARE NOISY.  Using a lot of ferrite cores got 
> their smallest one (100W) quiet enough on 40-6M to run the logging 
> computer for a CW QSO party mobile operation.
>
>>
>> If you use a power port (no longer called cigarette plugs), you will 
>> again introduce noise for your radio because they seldom have decent 
>> chassis bonding. 
>
> Chassis bonding is NOT a solution to noise in a vehicle. Noise does 
> not come in on the power wiring, it comes in on the ANTENNA. Indeed, 
> there is no good reason to bond a radio to the chassis of a vehicle.
>
>> They are also low amperage capable and you can exceed that (check the 
>> owner manual or the fuse block), even if momentarily.  Often they are 
>> also part of the vehicle systems array, so you'll get noises and 
>> generate issues to/from the vehicle electronics, some of which are 
>> rather spendy to repair.
>
> Many of the systems in a vehicle can generate noise, and some can be 
> quite sensitive to RF. One of the on-board computers in my Toyota 
> Sequoia (big SUV, same as their pickup) went into "limp home" mode 
> when I called CQ on 20M with 100W into a Ham Stick mounted to rear 
> side rail on the roof.  Top speed became 15 mph. I learned this while 
> driving I-80 through the Nevada desert between Salt Lake City and 
> Reno. Not a great place to break down. I got running again by pulling 
> the positive lead off the battery and reconnecting it, which rebooted 
> the victim computer.
>
> But this is an RF problem, NOT a power problem.  When we run mobile, 
> the only chassis bond that matters is the bond of the coax braid to 
> conductive parts of the vehicle at the antenna. This provides the 
> antenna with a counterpoise -- that is, the vehicle becomes a very 
> necessary part of the antenna. This causes RF current to flow on those 
> conductive parts of the vehicle chassis and body -- IF those body 
> parts are connected together. And that's a BIG IF, because most body 
> parts are insulated from each other by PAINT!
>
>> In the long run, it's best (and least expense) to simply run the 
>> (fused at both ends, both wires) power cable to a known, chassis 
>> bonded source.  Power is NOT a place to cheap out.  If you're QRP, 
>> it's simple, the wires aren't huge, check your IR^2 losses over the 
>> run (make sure there is no voltage drop AT the radio).
>
> I agree that I wouldn't power anything bigger than a talkie or 
> receiver from a lighter plug.  FAR better to run a beefy copper pair 
> directly to the battery. NEVER, NEVER use the vehicle chassis as a 
> return for DC. Doing so causes the positive lead to form a large 
> magnetic loop with the chassis return, AND causing it to act as an 
> antenna.
>
>> Hint:  Make sure EVERYTHING, power at the source, power at the radio, 
>> the radio itself AND the antenna are properly RF bonded (not DC) to 
>> the vehicle and you'll have less issues
>
> Again, the radio is NOT the sensitive element here, it's the ANTENNA, 
> which includes the chassis and other conductive parts. It IS important 
> that -12V be bonded at the battery, but it is NOT useful to bond the 
> radio.
>
> 73, Jim K9YC
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