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NSARC HF Operators 127 Nov08
HF OPERATORS
GROUNDSby
John WhiteVA7JW
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NSARC HF Operators 227 Nov08
WHAT GROUND?
! EARTH GROUND
! POWER GROUND
! SAFETY GROUND
! CIRCUIT GROUND
! RF GROUND
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NSARC HF Operators 327 Nov08
EARTH
! Earth is whatever the ground is." soil, rock, gravel, sand, water, clay, concrete, muck …
! Not an insulator, just medium to high resistance
! Think of each small volume of earth as a high value resistor
! All in parallel – more resistor, less overall resistance
! Total resistance can be small as volume increases
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NSARC HF Operators 427 Nov08
EARTH “RESISTANCE”
• Ground resistance is measured as Resistivity• Values are given in ohm-meters
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NSARC HF Operators 527 Nov08
EARTH “CONDUCTANCE”
! ARRL Tables ! Conductance in Siemens S = 1/R in S/m
! Other than salt water, earth is not good for antennas! S = 5, R = 0.2 ohm-m 10X better than anything else
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NSARC HF Operators 627 Nov08
EARTH GROUND
! Rods, Wires, Plates commonly used" Conductor resistance very small
! Resistivity of the earth is usually negligible because there so much of it available to carry current
• The limiting factor in electrical grounding systems is how well the grounding electrodes contact the earth, which is known as the soil / ground rod interface
" 1 ohm excellent" 10 ohms good" 100 ohms typical" 1000 ohms not good
! http://www.newarkinone.thinkhost.com/brands/promos/Earth_Ground_Resistance.pdf
Equipment
Earth
Rod
Wire
10 -100 ohms
0.01 ohms
0.01 ohms
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NSARC HF Operators 727 Nov08
POWER CIRCUITS
! AC Line - Equipment Power Supply – Transmitter
! Power ground is earthed
TRANSMITTERCIRCUITS
POWERSUPPLY
ServiceEntrance Power
Transformer
WallSocket
LineCord
Line (black)Neutral (white)Ground (green)
14 kV
Power LineTransformer
120VAC
0VAC
black
bare
white
EARTH GROUND
CIRCUIT GROUND
RF
TRANSMITTER EQUIPMENT
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NSARC HF Operators 827 Nov08
AC POWER CIRCUIT
! Hydro Transformer " primary side 14kV" return side earthed
! Secondary Side" 120VAC residential" neutral earthed
! Residential Ground" bare copper wire " earthed" third prong of plug" connects chassis
Chassis connection
ServiceEntrance
Tr
WallSocket
LineCord
Line (black)Neutral (white)Ground (green)
14 kV
Power LineTransformer
120VAC
0VAC
black
bare
white
EARTH GROUND
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NSARC HF Operators 927 Nov08
SAFETY GROUND
! Chassis connection is Safety Ground
! GREEN WIRE in cords and ground systems
! Protects against insulation failures
! Prevents YOU from becoming part of the BC Hydro power line circuit from Line (HOT) to Earth
! Do NOT disable this connection
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NSARC HF Operators 1027 Nov08
SIGNAL CIRCUITS
! Power transformer isolates direct connection to Hydro! Secondary to Power Supply
! AC to DC Operating voltages! All circuits have a common conductor! Circuit Ground
" low DC resistances" low AC impedances" common for all AC signals – audio , RF, control etc
TRANSMITTERCIRCUITS
POWERSUPPLYPower
Transformer
LineCord
Line (black)Neutral (white)Ground (green)
CIRCUIT GROUND
RF
TRANSMITTER EQUIPMENT
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NSARC HF Operators 1127 Nov08
CIRCUIT GROUND
! RF output of all modern transceivers is via SO-239
! Note RF connection to CHASSIS
! Output RF is developed between circuit / signal ground
! Has meaning INSIDE transceiver
! What about outside ?
! Is there an RF ground outside ??
TRANSMITTERCIRCUITS
CIRCUIT GROUND
RF
SO-239
CHASSIS
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NSARC HF Operators 1227 Nov08
GROUND SUMMARY
! Earth / Power Ground systems" equipment safety to prevent electrocution " operates at 60 cycles" long leads " engineered for low resistance
! Circuit / Signal Ground (inside equipment)" common signal path for all circuits" resides inside equipment" operates at kHz / MHz / GHz" short leads" engineered for low impedances
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NSARC HF Operators 1327 Nov08
QUESTION (Dave VE7DKR)
Q: In a radio station setup, what sort of a connection is made between the ground rod, or plate, and the soil/ earth. Is it:a) resistiveb) capacitivec) inductived) or a combination
1. All components are resistive – wire, rods, earth2. Voltage and current are in phase3. Therefore it is a resistor to earth, and earth is a big resistive medium of
tremendously varying value
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NSARC HF Operators 1427 Nov08
DOES RF GROUND EXIST?
! Here’s K9YC, Jim Brown’s opinion on the matterhttp://audiosystemsgroup.com/RFI-Ham.pdf
Ground Wiring: Some hams like to think of the earth as if it were somehow a "sink" into which all noise can be poured, never to bother us again. Indeed, you'll find lots of bad advice to solve RFIproblems with "a better ground." In fact, nothing could be further from the truth. An earth connection is rarely part of a solution to RF or noise problems.
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NSARC HF Operators 1527 Nov08
EARTH GROUNDS for RF?
! NO
! Earth Grounds are resistive and lossy
! OK at 60 cycles, but not suitable for RF
! RF means frequencies at MHz and GHz
! Grounding wire lengths comparable to RF wavelengths
! Wires connecting equipments and power systems to grounding systems present complex impedances, not low resistances
! Impedances are indeterminate
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NSARC HF Operators 1627 Nov08
But I NEED AN RF GROUND
! Problems with RFI ?
! RF in the shack - RF tickles and nips off station equipment
! Noise, Xtalk, Coupling etc ?
! Addition of a “ground” may change performance but doesn’t address the problem
! Changes to system impedances due to wavelength effects of ground wire simply move voltage and current nodes around
! Need to look elsewhere for root of the problem ….
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NSARC HF Operators 1727 Nov08
HERTZIAN ANTENNA
! Very FIRST antenna
! Heinrich Hertz – 1880
! Demonstrated ability to transmitand receive electromagnetic waves
! Balanced system
! No “grounds”
! The early Dipole
BALANCED DIPOLE
BALANCEDTRANMISSION
LINE
TRANSMITER
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NSARC HF Operators 1827 Nov08
MARCONI ANTENNA
! Earliest form of commercial antenna" Marconi Spark transmitters" operation well below 1 MHz" 1 wavelength >> 300 meters
! Hertzian dipoles not practical
! Operates against Earth Ground" earth is the “other half” of the antenna circuit
! Earth is not a good ground " salt water is unique and excellent" wire radials
VERTICALANTENNA
EARTH GROUND
TRANSMITER
Courtesy 1918 Wireless Telegraphers handbook
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NSARC HF Operators 1927 Nov08
SHIELDING
! RF is generated inside a metal box (the rig) ! RF is contained inside the cabinet
" conductive enclosure prevents radiation outside the box! Only (engineered) way out is through the Ant Jack > Coax! Coax contains RF between center conductor and inside
surface of braid
! Blue “fill” indicates area ofRF signal and is containedby the shielding effect of the cabinet and coax
! RF currents flow on SURFACE of conductors, not THROUGH
TRANSMITTER EQUIPMENT
TRANSMITTERCIRCUITS
POWERSUPPLYPower
Transformer
CIRCUIT GROUND
COAX
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NSARC HF Operators 2027 Nov08
DIPOLE ANTENNA
! Balanced (dipole) antenna looks like a 50 ohm resistor! R is the radiation resistance! Circuit is complete – no ground required
! Power Safety ground is connected from chassis to earth but plays no part in the RF circuit, coax or antenna system
BALA
NC
ED A
NTE
NN
A
TRANSMITTER EQUIPMENT
TRANSMITTERCIRCUITS
POWERSUPPLYPower
Transformer
CIRCUIT GROUND
COAX
Equipment Safety Ground
RADIATIONRESISTANCE50 ohms
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NSARC HF Operators 2127 Nov08
BAL ANTENNA with ATU
! Balanced Antennas with Antenna Tuner Unit ! Balanced line contains EM field (non radiative) ! No ground system required
TRANSMITTER EQUIPMENT
TRANSMITTERCIRCUITS
POWERSUPPLYPower
Transformer
CIRCUIT GROUND
COAX
Equipment Safety Ground
BALA
NC
ED A
NTE
NN
A
RADIATIONRESISTANCE400 ohms
BALUNATU
ANTENNA TUNER
BALANCEDLINE
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NSARC HF Operators 2227 Nov08
VERTICAL ANTENNA
! Radiation resistance of vertical antenna ~ 37 ohms ! Ground resistance appears in series with radiation R
" 8 ground rods / radial system maybe ~ 20 - 40 ohms wet" 1 ground rod > 100 ohms
! Antenna efficiency suffers / ground currents flow on coaxTRANSMITTER EQUIPMENT
TRANSMITTERCIRCUITS
POWERSUPPLYPower
Transformer
CIRCUIT GROUND
COAX
RADIATIONRESISTANCE37 ohms
GROUNDRESISTANCE100 ohms
VERTICAL ANTENNA
Equipment Safety Ground
RF current flowon outside of coax &
equipmentsbetween grounds Use ferrite on coax
to impede braid currents
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NSARC HF Operators 2327 Nov08
LONG WIRE ANTENNAS
! Use with an antenna tuner! ATU has to be connected to station ground (whatever that is)
! Ground wire is acting as a counterpoise is main component! Ground may be a minor component! RF currents flowing in shack can be a major issue
ANTENNA TUNER
Random Long Wire
Ground Wire
RADIATIONRESISTANCEUNKNOWNBALUNATU
ANTENNA TUNER
Station Ground
Jum
per
GROUND RESISTANCE100 ohms
XREACTIVECOMPONENT
Ground currents
COAX
COAX
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NSARC HF Operators 2427 Nov08
LONG WIRE ISSUES
! Excerpts from Practical Wire Antennas, John Heys, G3BDQ
! Advises counterpoise wires are absolutely necessary! Short counterpoises can be effective Google AA5TB
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NSARC HF Operators 2527 Nov08
RF GROUND FOUND !
! A, second line “.. Lack of an RF ground”
! It is not Earth
! It is a COUNTERPOISE
! RF Ground is a misused description for the missinghalf of vertical and long-wireantennas
Courtesy of ARRL QST Jan 06
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NSARC HF Operators 2627 Nov08
Summary
! The Station Ground is a Safety Ground to Earth
! Circuit Grounds exist inside equipment
! RF Ground means COUNTERPOISE
! Some housekeeping rules to keep RF out of shack" Use counterpoise for “one sided” antennas" Ensure all signal leads are well shielded to control egress of RF from
Transceiver" Ensure all power leads are well filtered" Ensure all control leads, if not shielded, are bypassed" Employ Ferrites and Baluns on feed lines