[Elecraft] grounding K2

[Stephen W. Kercel]

Scott:

If you do not have noticeable RF on the chassis, as you should not 
have if you are using a dipole with low swr, the ground connection 
does not do much for you. If you're running a random wire or Windom, 
you might have RF getting back into the shack and some of it might 
find its way back to the K2. Then you need an rf ground for the 
chassis of the radio.

In that case you need as short and direct a path as possible to RF ground.

Remember that you have three distinctly different grounding problems, 
with conflicting solutions.

1) The powerline safety ground. If your house wiring is up to code, 
and if you are using a power supply whose AC input uses a three-wire 
plug properly wired, you need do nothing further about this. CAVEAT: 
Do NOT use the house wiring ground as an RF ground; you are very 
likely to have a resonance at an HF ham frequency and this can cause 
you all sorts of EMI problems. In my setup, I have MFJ ferrites on 
the DC lead between my K2 and the power supply, and on the AC power 
lead of my power supply.

2) Lightning ground. If you use polyphasers or a Wireman ground bus 
or some other device to keep lightning out of the shack, that needs 
to have its own ground rod. You want lightning-induced surges to have 
as short and direct a path to ground as possible. CAVEAT: To meet 
code, this ground rod must be bonded to your house wiring ground by 
at least a #6 copper wire.

3) RF ground. There is no good RF ground. At HF frequencies any 
finite wire has non-trivial inductive reactance. According to an 
Army-Air Force study (that I often hear mentioned, but for which I 
cannot find the report), the least unacceptable HF RF ground is a 
wire a half wave length long at your lowest frequency, buried one 
inch below ground surface, and connected to 1 foot ground rods spaced 
every 8 feet. Deep burial of the wire or longer ground rods are no 
help because HF RF only penetrates about 3 inches into average 
ground. If you cannot run the wire in a straight line, a meandering 
path will do. For safety reasons the wire should be #6 copper. To 
meet code this wire should be bonded to your house ground via #6 
copper wire. To keep the RF out of the house ground, use ferrites on 
the bonding wire very near its connection to the RF ground wire. The 
ferrites will not interfere with lightning or electrical fault 
current passing through the bond wire; most of their energy is well 
below 1 MHz, and the MFJ (and similar) ferrites start to roll off 
just below HF. CAVEAT: At HF frequencies, ferrites such as MFJ have 
2-3 dB attenuation; you need to use at least 6 ferrites to get any 
useful reduction in undesired RF.

If you do not use an external antenna tuner, the K2 chassis should be 
connected to the RF ground by as short and direct a wire as possible. 
If you use an external tuner the tuner chassis should be connected to 
the RF ground by as short and direct a wire as possible. In this case 
if you put 6 ferrite beads on the coax between the K2 and the tuner, 
the combination of the tuner grounding and the ferrites should keep 
RF off the chassis of the K2. In that case, you might want to leave 
the K2 chassis ungrounded to avoid forming a ground loop.

FINAL CAVEAT: As with antennas, RF grounding is as much witchcraft 
and magic as it is physics. The practices listed above work most of 
the time but not always. The grounding system of any specific station 
might need to be tweaked to eliminate EMI and other problems. For 
safety reasons the ground system should be code compliant. Code 
compliance will not solve any EMI problems or make your station get 
out better, but it will keep you from getting killed.

73,

Steve Kercel
AA4AK




At 02:19 PM 4/16/2008, Scott McDowell wrote:
>Hello
>Has anyone ever felt the need to ground their K2, and if so, where did you
>connect the ground wire to the K2?
>Thanks
>Scott
>N5SM
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