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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