Message-ID: <000301bed7c3$1be5eb80$3a5eac3e@default>
From: "Alan Melia" <Alan.Melia@btinternet.com>
To: "rsgb_lf_group" <rsgb_lf_group@blacksheep.org>
Subject: LF: Earths, grounds, or counterpoises
Date: Tue, 27 Jul 1999 00:47:01 +0100
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Hi all,
I have followed some of the discussion on grounding recently and a few
questions occur to me..

Bearing in mind that most seem to be feeding their aerials with 50ohm coax
......
a) what is the effect on the 'balance' at the end of the coax of having two
ground systems within the near field of the aerial? Does it matter?Do you
link couple to the tuning  coil?
b) does it make a difference if you use a balanced feed? Does anyone?
I am wondering whether currents induced in the braid could be problem.
Anyone tried a separate 'shielding' over the coax? What was it connected to?

Extra radials/earth systems don't seem to help.
As the parasitic elements of a yagi sit in the near field of the radiating
element, and the length of these elements determines the phase of the
currents induced in them .....
a)Is it possible that the currents induced particularly in short radials
will differ in phase with the length and the orientation of the radials.? So
making addition complex.
b) has anyone tried to measure the current induced in the radials? a clip-on
RF ammeter should read something, though I am not sure whether it would be
necessarily meaningfull (I'm a "make loadsa measurements first and work out
what it means afterwards" guy)
c) Is 'longer' better than adding more shorter 'radials'?
d) Les Moxon in his book "HF Antennas for all locations" covers the topic of
'compressed' radials (or counterpoises) ....resonating short radials with a
coil or using a helical element. Has anyone attempted this? I suppose it
should get more current flowing in the radials, which ought to affect the
signal, or is it a bodge to let the coax see something more reasonable. A
local friend of mine has achieved interesting results by feeding a
counterpoise through an 'ATU' on 80m.(at least it got the RF out of the
upstairs shack).
I'm not really expecting answers, these are just questions that occur to me.

Mains Earths (grounds)
Are we being too naive in believeing the mains ground to be a good one?  I
have overhead local distribution here (for the Antipodeans, East Anglia is
the UKs outback!) My mains earth in a piece of 1inch (25mm) diam copper pipe
3feet (1m) long. There is no strapping to the water pipes as most are now
plasic the cast-iron having given up the struggle a few years ago. In the UK
it is not the practice to strap the Neutral to earth at the consumer
premises (except where there is PME?). I believe (from a radio amateur
working for the local supply company) that great efforts are made to get a
good ground at the local transformer (sub-station) and the target is 1ohm
(measured at 50Hz of course). I remember doing a check on a 5foot copper rod
in my sandy ground, away from the house where the soil is slightly more
moist and getting a value of about 80ohms.
 The technique (don't try this at home children!) was to connect one end of
a current limiting resistor (a 1kW electic fire bar) to the 'Live' side
('Phase' in some countries, I believe) and the other to the radio 'ground'
system. A high impedance Alternating Voltmeter was then used to measure the
voltage between the ground system and the Neutral line.
Knowing the current going into the 'earth'  (Vmains-Vneutral)/R and the
voltdrop (Vneutral) caused by that flowing into the ground resistance, you
get a value for the earth resistance. Since the Neutral is strapped to a
good ground at the sub-station, the Neutral acts as a 'sense' wire (high
impedance is necessary so there is no volt drop on the neutral wire
resistance.)
 Using this technique I got down to 7ohms with three 5foot (1.5m) stakes
joined by a length of 0.25in (6mm) copper bussbar buried about 6in (15cm)
down. This doesn't work if you have an RLCB tripping on 'unbalance'
condition, and an isolating transformer will be needed.  These values, I
believe, would have no relation to losses at 136kHz, but it would be
interesting to compare them.
It could also be a problem if you have PME, so do be careful.
I was warned that the only trouble with having a really low resistance earth
was that if a neighbour had a Neutral fault you would take all his fault
current. I believe a least one telephone exchange, adjacent  to a
substation, suffered that problem, and was upgraded long before planned!
This may be a good reason for keeping earth separate!

A bit long I'm afraid but hope its of interest/use
73 de Alan G3NYK
Alan.Melia@btinternet.com