[Elecraft] linking K3 with PC via blue tooth

[Jim Brown]

On 12/13/2010 6:41 AM, John Ragle wrote:
> My education needed: why would (in principle) using a Bluetooth
> connection to a K3 remove "PC interference?" All the clocks and
> clock-generated sharp-edged waveforms will still be present...
>

RFI often happens by more than one mechanism.

Most RFI  is radiated by conductors acting as antennas. Those conductors 
can be INSIDE the box, AND OUTSIDE the box.  Also in general, the longer 
the wire, the better it is as an antenna at HF. When you reduce the 
number and length of wires connected to the box, or when you choke them 
to kill RF current on those wires, you take them out the picture, and 
are left with radiation from INSIDE the box due to its poor shielding 
(and poor circuit board layout).  This radiated RF is picked up by the 
ham antenna, so the distances that matter are the distance between the 
noise source (computer) and that antenna.

For example -- many laptops will radiate trash, especially on some of 
the higher HF bands via their power cable. If you remove the power cable 
and run them on battery, the trash sometimes goes away (or gets weaker).

Nothing you can do with external cables will kill radiation from wiring 
inside the box, so when you choke the cables, that radiation will still 
be there (but weaker, because the antenna is shorter).

RF trash can also be CONDUCTED via Pin One Problems in both ham gear and 
computers when they are interconnected.   Pin One Problems put RF onto 
so-called "ground" contacts (for example, inside the computer at the 
serial or USB port), and Pin One Problems couple RF from an improper 
shield connection into the radio.   For this mechanism, no antenna 
action is involved -- the RF is conducted on the cable shield because 
the shield is not properly connected on both ends.

For a tutorial on the Pin One Problem, and how to deal with RFI, see

http://audiosystemsgroup.com/publish.htm   and

http://audiosystemsgroup.com/RFI-Ham.pdf

Another common coupling mechanism for RF trash is Pin One problems in TV 
sets and other consumer electronics putting that trash onto the shields 
of cables (like the CATV cable), where it is then radiated by the CATV 
system.


73, Jim Brown K9YC