[Elecraft] Best way to secure RF ground from 2nd floor?

[Ron D'Eau Claire]

The problem you face is getting a non-reactive connection from the rig to
the ground. 

Any conductor connected to the earth at the ground level will be grounded at
that point and will be "above RF ground" at the other (rig) end. If you
happened to have a 1/4 wavelength wire between your rig and  the ground,
you'll have the highest possible RF voltage on your rig! Anything other than
1/4 wave or an odd multiple thereof, will show more or less RF voltage. It
won't be a "good RF ground". A 1/2 wave wire between your rig and a ground
rod will show a good RF ground at the rig end: duplicating the impedance at
the ground rod, but only at the frequency where it's a half wave or a
multiple of 1/2 wave.  

Usually the best way to "ground" a rig for RF that isn't near real ground
(less than, say .05 wavelengths at the highest frequencies you use or, on 10
meters, 0.8 feet maximum between the rig and the ground pipe, or 7 feet on
80 meters) its to use a 1/4 wave wire attached to the rig whose far end is
well insulated from ground. With the far end insulated, it will be forced to
be at a voltage loop or high impedance point. That puts the other end, at
the rig, at a current loop or low impedance point. You can still use a wire
to your ground rod in parallel with that if you like although most
electrical codes frown on having a ground separate from the mains utility
ground. 

Another approach for an RF ground is to use your connection to the ground
rod, but tune out the reactance. MFJ made a small "tuner" for just that
purpose: a coil and capacitor in series that one adjusted as needed to
produce maximum ground current at the rig. That can be very effective, but
it is frequency-sensitive: it requires readjustment for every band. And,
because the circuit involves a capacitor in series with the coil, it is not
a d-c ground if that's what you are looking for. But it can produce a good
RF ground. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of DOUGLAS ZWIEBEL
Sent: Monday, February 18, 2008 4:23 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Best way to secure RF ground from 2nd floor?


HI all:

I am re-doing all my 20 year old connections here in the shack, which is on
the 2nd floor of my house.

Can anyone point me to a resource for the "best way" to ensure a proper RF
ground from the 2nd floor?  I have lots of holes in the walls going outside
(rotor cables, control lines, many coaxes, etc), so going through the wall
is not an issue.  If fact, maybe I can use the shield of a coax to help with
an earth ground?  I"m not looking for "resonant" inside radials....I want a
genuine RF ground.

Looking forward to your comments.

Since I suspect this may a topic of wider interest, I'll ask you post your
comments here (or you can always post to me directly if you disagree with
"filling up the reflector").

Thanks so much!

de Doug KR2Q
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