[Elecraft] Mobile operation RFI from QRO (was KPA500 mobile)

[Jim Brown]

On Sat,4/15/2017 8:55 AM, Colin Brench via Elecraft wrote:
> My expertise is in EMI control and so I can provide some background to how unexpected things happen.

Great post, Colin.

> RF fields around the antenna will be high and most mobile antennas have a low input impedance.  To fully understand EMI risk you need to understand where the RF current will go, and simply put you need to consider the antenna as every conductor in the vicinity of the actual radiator.

This is FAR too simplistic a view. The metal body, chassis, and frame 
serve as the counterpoise for the antenna. These metal parts of the 
vehicle are the return for antenna current and for the field generated 
by the antenna. This makes them part of the antenna, they are carrying 
as much power as that vertical radiator we CALL the antenna, and current 
will be distributed around the vehicle's metal parts just as in any 
other antenna. The only difference between current distribution in the 
vehicle and in a wire is that the shape of the vehicle is very different 
from a wire, so that modeling it is far more complex. This current can 
easily couple into vehicle wiring running in proximity to that current. 
And, since the VEHICLE carries RF current, the vehicle itself is part of 
the radiator.

73, Jim K9YC