A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical.
Usually a potential difference in the grounds causes a current to flow in the interconnects. This in turn modulates the input of the circuitry and is treated like any other signal fed through the normal inputs. Lots of designers count on ground being ground and do not optimize their design to eliminate their sensitivity to ground noise.
Ground loop is a common problem when connecting multiple audio-visual system components together, there is a good change of making a nasty ground loops. Ground loop problems are one of the most common noise problems in audio systems. Typical indication of the ground loop problem is audible 50 Hz or 60 Hz (depends on mains voltage frequency used in your country) noise in sound. Most common situation where you meet ground loop problems are when your system includes equipment connected to earthed elecric outlet and antenna network or equipments connected to different grounded outlets around the room.
Everything connected to a single mains earth, which is usually connected to all the earth pins in all the power sockets in one room. Then antenna network is also grounded to same grounding point. This would normally be okay, as the grounding is only connected to each other in a star-like fashion from a central earth wire (leading to the real Earth via a grounding cable or metal pipe) earth cables run through your power cables into the equipment.
Once you take into account that some of your equipment is linked with shielded cable you are quite likely to face some problems. Currents could quite possibly run from one piece of equipment, into the earth cable, into another piece of equipment, then back to the first piece via a shielded audio cable. That wire loop can also pick up interference from nearby magnetic fields and radio transmitters.
The result is that the unwanted signal will be amplified until it is audible and clearly undesireable. Even voltage differences lower than 1 mV can cause annoying humming sound on your audio system.
A problem with audible noise coming from your audio system when other electronic components (fridge, water cooler, ect.) could be the result of of a contaminated ground/neutral conductor in your A/C wiring and a ground loop in uour audio system. This can happen when certain type of devices come on. Typically their power supplies are non-linear and throw garbage back onto the neutral and/or ground conductors. Usually line conditioners or UPS devices will not do anything to help solve this problem.
In the construction of most commercial buildings, one ground is usually run throughout the building to keep the impedance as low as possible. Unfortunately there are other electrical equipment such as air conditioning units, refrigerators, washers/dryers and other high current devices connected to the same ground. Thus the chances of getting a clean ground in a typical audio visual installation is slim, especially in large commercial buildings, hotels, hospitals or convention centers.
A typical office wall outlet has three electrical connections, which are the "hot", "neutral", and "grounding" wires. All office equipment requires only the hot and neutral wires to function. The third or grounding wire is connected to exposed metal parts on the equipment. Within the building, the grounding connections of all electrical receptacles are wired to one another and are connected to the water piping. This ensures that all electrical equipment with exposed metal parts has these parts electrically connected to each other and to exposed metal fixtures in the building such as water fixtures.
The hot and neutral wires are interchangeable as far as the equipment is concerned. Both are power carrying wires. One of the power carrying wires is grounded for reasons of safety. In Europe, the normal 3-wire receptacle is symmetrical so that the neutral and hot wire connections can be swapped by simply rotating the plug.
The 3-wire system that the user sees is actually derived from three phase distribution, which uses a 5-wire system. In the 5-wire system, there are 3 hot wires, 1 neutral wire, and 1 grounding wire. The common 3-wire receptacle uses only one of the 3 hot wires.
This 5 wire wiring system is basically good and it is used in most buildings and places where ground loops are expected to be a problem. The most problematic are those builing whic are wired using 4 wire 3 phase wiring And worst of all is a 2 wire 1 phase jack wiring where neutral and ground share a common wire. This practice is very often used in older buildings in Finland and causes terrible ground loop problems even between nearby power outlets. If your are planning to install any dedicated equipments (computer connected to LAN, interconnected audio or video equipment etc.) to building which has this kind wiring system is advicable to get a lincensed electrician to rewire the room with proper outlets. This wiring has also some other problems and that's why it is not allowed anymore in new installations in Finland.
Circuit breaker boxes: The main breaker box to the building is the single location where the neutral and the ground wires come together. The electrical service will be grounded at this point. IN ALL DOWNSTREAM BREAKER BOXES BOTH THE NEUTRAL AND GROUND WIRES MUST BE KEPT APART FROM ONE ANOTHER. Otherwise you will have neutral currents flowing on the ground wire. This is extremely important and is a major safety and signal issue.
These simple rules apply to ALL cabling including CATV, Video, AC and signal. One exception is the ethernet. Ground the computer LAN one end (preferably to the same point as your audio system) and make sure that the thin ethernet connector metal parts do not touch any parts of computer case (there are nice plastic isolation cases available for them). I would recommend to use 10 Base-T ethernet which used twisted pair wiring because it does not need any grounding and does not cause ground loops in any case.
Many new buildings in USA are equipped with "Isolated ground" receptacles. These are normally recognizable because they are bright orange and have a triangle marked on the face. Basically, these receptacles have a separate "green wire" equipment ground, and the wire goes back directly to the circuit breaker panel, without being connected to anything else. Isolated ground receptacles are installed in the hope that electrical noise generated in the building, or by other pieces of equipment, will not disturb the operation of delicate computer equipment plugged into them.
Most electronic equipment is sensitive to ground loops and ground-induced noise. A proper earth ground at the building services entrance is the first step to avoiding such problems. In many cases, a proper earth ground is provided by a connection to the steel rebar in the building's foundation.
All outside service grounds must be solidly connected to this ground point, including power, telephone and cable television. For lightning protection, any antenna masts should be grounded here as well. Ground connection points from the telephone system controller, security alarm panel, audio equipment and other electronics gear should be connected to this ground buss. All distribution of 3 phase voltage inside of building should be done using 5 wire system. Distribution of 1 phase power should be done using 3 wire system. The safety ground wires should be interconnected in star or tree like fashion. For more information check Residential Wiring and Grounding Guidelines from Power Clinic.
If possible, all electronics and computer equipment should have a separate isolated electrical subpanel with isolated ground receptacles provided at all locations remote from the main. Isolated ground means that the ground wiring is otherwise isolated form all other wiring except that it is connected to the main grounding bar for one single point. This practice will ensure that all electronic equipment grounds are at the exact same electrical potential and avoid the "minute differences" in grounds that cause ground loops. These differences are reflected in signal-carrying conductors or shields between the components and may be amplified to audible or visible levels.
Components that cannot have "equal-potential" grounds should have signals that are isolated from each other. This can be expensive and difficult to achieve. It is much easier to prevent the problems in the first place when designing the electrical distribution. More information on that is available from Equitech articles: Power Management in the Studio, Audio Wiring and Grounding, 1996 National Electrical Code Technical Support Bulletin and Installing a Technical Grounding System. Those articles provide you understanding how to make good grounding system for studio.
Do not try to modify your electrical wiring yourself. When you know what needs to be done call professionals to do the job properly (you might need a special consultant to do the plans for modifications because standard electricians don't usually know all the special requirements audio studio has). When you have proper groundung system in your studio then you can start doing the the audio wiring in a right way. You can easily easily make your system very sensitive to power system noise if you do not do the wiring properly. Rane application note Sound System Interconnections gives you good undertanding how the audio connections should be done.
The problem is that in many cases you don't have possiblity to change the electrical distrubution system already in the place, because it will come hard to do and expensive. Then you have to live with what you get and try to solve those problems with suitable isolation devices.
The quipments connected to metal audio racks will get connected to each other through the metal rack. This can lead th ground loop problems if the wiring is not done carefully. If you face this type of problems do not use insullating tape or other non-conducting materials to "cure" the problem. That could end up being very dangerous. Instead think of a redesign.
Assuming that this rack is the hub of your plant then proceed as follows. It's called hub and spoke grounding.
Begin with an empty rack, standing in the middle of the floor. First, bring AC to the rack, allowing for expansion. Buy one or two five-foot pieces of wiremold with recepticles spaced every four inches. Bond the green wire from the recepticles to the rack so that the rack is at the same electrical potential as the earth ground for the AC. You can add more racks and wiremold strips as needed until you have adequate rack space. Bolt all racks together until there is NO question that they are electrically just one piece of metal.
Mount the power supply for the console in this rack. Mount all outboard equiopment in the rack. View the rack as a hub for ALL business at your plant. Start substituting the word "hub" for rack.
Spoke #1: Run a single piece of grounding from the hub to the console. Make it big. Wire the power supply to the console. Now cable other console items back to the hub. NO OTHER COMPLETE ground connection allowed between hub and any other terminal point: Open the shield, for the sake of unformity, at the terminal end for every piece of shielded cable, leaving each shielded cable grounded at the hub end. Your single piece of grouding is what keeps it all safe -- and silent.
Spoke #2: From the hub, run AC to, perhaps, a free-standing tape machine. Ground it back to the hub. As above, run signal cables to the hub, grounding the shields at the hub only.
Spoke #3: From the hub, run AC to, perhaps, a rack in another studio in your plant. This new rack becomes a hub for the world it lives in and it has ground wires emanating from it to new terminal points.
Spokes #4 through 400: As above.
NEVER NEVER NEVER: Here it is, here is what keeps it all honest and hum-free: NEVER take a shortcut and run a cable directly from one terminal point to another. ALWAYS run such cabling back up the hubs spokes to the main hub and then down the appropriate spoke to the desired terminal point, tapping into hub grounds all along the way.
Buy a digital clamp-on current meter. There should be NO current on any ground wire. None. If you can measure current flow on a ground wire then fix it: you either have a circular path or else a faulty piece of equipment.
If you can't get clamp-on meter you can try to measure the current flowing on audio cables by removing the cable from one and and connecting an ordinary multimeter between the ground pin in the audio wire and the audio connector ground pin in you equipment it was connected to.
Getting rid of ground loops are not easy. Finding them is even harder. LiveDV magazine has published a good tutorial Soundings: Getting Wired how to find and solve ground loop problems in typical home AV system which consists of computer and other AV equipment (receiver, amplifier, VCR etc.).
The only acceptable method for testing is to remove and disconnect everything. Then reinstall the equipments and connection piece by piece. Stop when the hum becomes audible, and fix the problem in the last piece of equipment that was installed.
If you have equipments connected to many power outlets, then try to connect them all to one grounded extension cord and then plug this cord to one grounded outlet. This solves usually many problems, because this creates star-like grounding scheme for those equipments.
But the following star grounding scheme is effective if the equipments do not have any direct connection to other equipment grounded elsewhere (transformer isolated connections are ok).
For example if you connect your TV to otherwise humless audio system you
will quit epropably hear a humming noise (50 Hz or 60 Hz depending on the mains
voltage frequency)
caused by current flowing between your equipment and the antenna connection
in the TV. The following example is a typical home setup where you have your
multimedia computer TV and connected to your stereo system:
+----+ +-----+ +----------+
<--------------| TV |===============| AMP |===============| Computer |
cable TV +----+ audio cable +-----+ audio cable +----------+
The most effective way to stop this 50 Hz or 60 Hz noise is to break the
galvanic connection which causes the ground loop. You can either connect
an isolator to the antenna wire:
isolator +----+ +-----+ +----------+
<-------**-----| TV |===============| AMP |===============| Computer |
cable TV +----+ audio cable +-----+ audio cable +----------+
or putting on isolator to the audio line:
+----+ +-----+ isolator +----------+
<--------------| TV |===============| AMP |=====**========| Computer |
cable TV +----+ audio cable +-----+ audio cable +----------+
This is the only effective ans safe solution to
problems which deal with grounded outlets and radio/TV cable/antenna
connection.
Breaking of ground loop can be done in many ways, some which are better and some are less good. Logically you could think, you could eliminate ground loops by disconnecting the power-cord ground pins on all your gear. Do not do this. Removing the ground connection isn't safe without special equipment and can defeat the actions of your noise filter or spike protectors inside the equipments. Removing the ground connection from the equipments which have it is dangerous, against electronic safety regulations and you risk damaging your equipment. If you absolutely have to break away from the power ground, have an electrician install ground-fault interrupters (this method applies to USA only) or isolate yourself completely from the power company with a special transformer. But if you're going to go to the trouble of doing this, you might as well consider rewiring your studio with professional balanced gear and proper star grounding system.
Solving the ground loop hum problem using the right ground loop isolator is the safe, effective way to eliminate unwanted hums at an affordable price. Typically ground loop problems can be solved with audio isolation transformers connected to the audio line. There are also commercial audio distribution amplifiers which provide this isolation.
Regardless of what type of ground loop isolation method is used, remember, never remove the ground prong on the power cable.This may work as a temporary solution, but personal safety should not be compromised.
If you can't find the ground loop and don't want to use isolation transformer, try tempting the circuit with an even better ground. Heavy-gauge wire has very little electrical resistance, so less current is likely to flow through the shield. Get some heavy gauge wire and run lengths of it from your computer's chassis to each other chassis. On audio equipment, there's usually a screw marked for this purpose. You should hear the hum go down as soon as you make the connection. If heavy-duty ground connections don't stop the hum, you'll have to use suitable isolator in that audio line.
Direct boxes are devices that convert unbalanced instrument-level (or line-level) outputs into balanced, microphone-level inputs. They are used heavily in large, arena-size sound reinforcement systems where the keyboards, etc., are located far away from the mixer. Impedance differences between the keyboard and mixer prohibit one from running cables directly out of the bass amp of keyboard and to the mixer.
To use the Direct Box, one takes the guitar amp's output (it usually has one on the back), and, using a 1/4" patch cable, plug the other end into the direct box input. Make sure that the switch (if it has one) labeled "Speaker/Instrument" is on "Instrument." Plug a normal XLR cable into the output end and the other into your cabling which goes to the mixer.
If the system is grounded at bothe ends and ground potentials start flowing, you'll get a ground loop. Ground loops can be identified by a low hum (60Hz in the US and 50 Hz in Europe) through the sound system. First place to check: direct box. Direct box usually has a switch labeled "Ground Lift" for solving this type of problem. The ground lift switch will lift the ground (safely) and the hum should stop. If the switch isn't there, use a special ground lift cable on the XLR cable. Do not, by any means, disconnect the grounding pin of the AC cord.
The current which fows in the ground loop flows through audio cable shield. If you cut the audio cable shield the current will stops flowing but exposes this audio line to other kind of problems: if one of the equipments is not connected to electrical grounding, then the equipment don't have any common gound which then not to work as expected. To avoid this kind of problems and still limiting the current passing in cable shield wire to value which does not cause problems an scheme called ground lift is introduced. Ground lift places a resistor (usually around 100 ohm) between the equipment ground and cable shield. This resitor limits the current passing in the ground loop situation, but still provides quite good ground connection. This system is unfortunately quite sensitive to radio interference, so the 100 ohm resistor is usually shunted with small capacitor (usually 4pF to 10 nF) which makes the impedance to be low at radio freqwncies but does not let too much 50 Hz current flowing.
1 (not connected) 1 2 --------------- 2 3 --------------- 3This is the most basic ground lift circuit which works nicely when all equipments are grounded and have balanced inputs/outputs. Because the cable shield is cut the cable this arrangement makes the cable more prone to pick up radio frequency interference.
10 nF +---||---+ | ____ | 1 -+-|____|-+- 1 100 ohm 2 ------------ 2 3 ------------ 3This ground lift connection does not fully cut the gound carrying cable shield, but icreases the resistance so much that the currents which would flow in the shield in typical ground loop situation are limited to so low values that they have no effect in system performance. Because the ground is not completely cut then the circuit also works also when ungrounded consumer equipments with RCA->XLR adapters are connected to the system. The capacitor makes sure that the cable shield appears to be continuous to the radio frequency signals (radio frequency interference protection provided by shield is not lost). This circuit is quite universal and I have used this circuit for succesfully solving some balanced circuit ground loop problems.
Situations where two grounded equipments with unbalanced connections
are connections have ground loop related humming problems and no other
solution helps then you can try to use ground lift. Ground lifting
in inbalanced connections works only efectivily when both of the equipments
are properly grounded to same point (in other cases the problems typically
becomes worse if groound lift is used). Here is a typical ground lift
circuit for unbalanced connections:
Signal -------------------- Signal
Ground (not connected) Ground
Try this circuit only if you know that both equipments are properly grounded.
If the equipments are properly grounded this circuit will cause enormous
amounts of humming and potentially damage the input amplifier of the
receiving equipment because of the flowing stray currents on the ungrounded
equipment. The best solution for solving unblanced connection ground loops
is using audio line isolation transformer.
Ground lift circuit would reduce possibilities of audible ground loops. A truly covers-all bases piece of equipment would have a switch to activate or deactivate the ground lift. To test if your equipment has ground lift, insert a balanced TRS or XLR cable into the equipment, and measure the resistance between the shield contact of the exposed connector and the casing of the equipment or the earth pin of the mains cable of the equipment, using a multimeter. If there's a 100ohm to 500ohm resistance, your equipment is ground lifted.
Ground lift is quite effective in balanced audio connections, but is much less useful in unbalanced connections, which is the connection type used in almost all consumer audio equipments. You might try this ground lift scheme with this connection type, but the results would be much worse. Even when you can limit the shield connector current to values which do not cause problems, there is still the ground potential difference between equipments which gets amplified (and you get still some 50 Hz noise). Even ground potential differerences much lower than 1 mV can cause serious noise problems with unbalanced circuits. If you have unblanced connections, I would advice you to use audio isolation transformer instead of ground lift when you are solving problems with nonbalanced audio connections.
Audio Wiring and Grounding article from Equitech web site provides more information how ground lift is wired and hiw it affects the audio system performance.
You can easily test the effectiveness of ground lif in your system. urn the volume down, disconnect the shield at one end, and slowly bring the volume back up. It's easy if you've got phono connectors--just pull the plug partway out, so the pin makes a connection but the outer shell doesn't. Be warned: If other grounds aren't good enough or mose of the equipment are not grounded at all this will cause an even worse hum.
If you want to do the ground loop elimination in audio path, you have to cut the galvanic connection but pass the whole audio range. The simplest and most common way to do the isolation is use audio transformer which is ment for audio use. Transformers for audio use have some problems like distorted bass response and attenuating in high-frequency response. Basically a transformer slows down upper frequencies and allow the low frequencies to pass first, creating what we perceive as a "fat/warm" tone. Inadequate frequency response on the low end (rolloff at like 20Hz), causes low frequencies to be "slowed", allowing the upper frequencies to be heard first, this is perceived as "barky/ brittle". High-quality audio transformers cover whole audio band with good response, but those are quite expensive.
There are ready made circuits available from shops selling car audio stuff (ground loops are usually problem also in car environment). If you live in USA, take a look in Radio Shack's catalog on car electronics or check the Radio Shack Product Support pages which have specifications of Ground LP Isolator (270-0054) which cost about $15US. For more professional product check JK Audio Pureformer Stereo Isolation Transformer. Those products seem to be quite suitable for solving ground loop problems in consumer audio systems, but I have not tested them myself. Europeans should take a look at their nearest dealer which carriers Monacor prodicts, because Monacor's new catalogue lists FGA-40 (Best.-Nr. 06.4370) Ground Isolators which are 1:1 audio isolation with 10 kohm impedance (look quite good on the catalogue).
For professional audio use buy high quality commercial audio isolation/balancing transformers (those are very handy to keep around to solve unexpected ground loop problems). DI-boxes are also used to solve ground loop problems in a PA situations where different instruments are connected to mixing desk. Most DI boxes are active and are almost useless are getting rid of earth loops and stopping buzzes & hums etc. A GOOD passive DI which provides isolation is the only way to go.
If you want to build one yourself, you have to get two audio transformers which have 1:1 transformation ratio and greater than 1 kohm impedance. There are high quality audio transformers in the markes that meet those specs, but those can be quite expensive. Another option it to use 600:600 ohm isoltation transformers widely available for telecommunications and other uses. Those are not that high quality as good audio transformers, but can be well adequate for many not so demanding multimedia applications like computer audio if suitable transformer is selected.
I built my isolatiors usign two high quality telephone line coupling transformers which have 600 ohm impedance. This is the most commonly transformer type used in high-speed modems. Best of those are quite wideband devices (far more bandwidth than usual 300-3400 Hz as used in telephone). Using two of those transformers and few RCA connectors made quite satisfactory (but not really hifi) audio isolator. The connetion is easy: connect primary side of the transformer to one audio connector and secondary to other.
I used EOP Z1612 transformers in my test circuit and got quite acceptable frequency response of +-1 dB from 40 Hz to 20 kHz as you can see in figure below. The bass frequency below 40 Hz is not good.
The frequency measurements were made with Nacamichi T-100 Audio Analyzer and the isolator circuit was connected between it's 600 ohm output and 50 kohm input. I don't know if EOP Z1612 transformers are still available at Farnell, but you can try. If you are looking for other high quality transformers which could be a used, I would try ETAL P2001. I haven't been able to test their performance in this application, but they have proven to good transformers in other laboratory test and applications. Avoid cheapest telephone and audio transformers, because their performance is very poor at frequencies over about 5 kHz (for example Radio Shack (273-1374)).
A ground loop in your AV system caused by antenna connection or TV cable is very common if you have your computer connected to the same system. This type of ground loop problem can be solved by using suitable isolation between your AV system and the antenna cable. The simplest way to get rid of the hum is to disconnect the antenna cable from the AV system. If you still want to watch cabe TV or listen to your radio an dkeep the system hum free then you have to install isolators to all those antenna cable connections your system has.
Best solution to antenna/cable caused ground loop is to add a 1:1 transformer in the antenna signal, floating the VCR with respect to the cable tv ground. This solved the hum, no need for a messing with the audio signal, and the tv image quality did not suffer (most tv's get an overdose of signal from the cable tv anyway).
You can simply make such a 1:1 transformer:
I have seen another transformer circuit posted in the usenet. Kari Hautanen wrote an article to sfnet.harrastus.elektroniikka newsgroup about antenna isolator. The article says that you can built a suitable transformer using following method: Primary and secondary are three turns of 0.2 mm Cu-wire wrapped around small magenta coloured toroidal ferrite core. Seems quite simple, but the article did not mention the exact core size. It mentions the source of the circuit to be a book Osmo A Wiio, Reijo Laine, Radioamatöörin käsikirja, EU Harrastekirjat 1978, 1980, page 164. I have not been able to locate the book to check the circuit, but the circuit in one ready-made isolator had very similar circuit:
On the picture above you see the whole adapter and the picture below is close picture of the details inside the antenna isolator adapter.
It had three turns of thin wire in promary and secondary wrapped around small ferrite core. The wiring inside the isolator is very similar to the audio isolator circuit, the only difference is that now connectors are antenna connectors and the transformer is the one designed for antenna signals (described above). The thin wires between the transformer and the coaxial cable are kept minimum to avoid the adapter to pick up interference.
If you live in Finland, you can buy this type of isolation adapter from SUOMEN RADIOAMATÖÖRITARVIKE OY under name J A-A Junction häiriöadapteri televisioon. It costs 43 mk (about 10 US dollars).
For more ideas how to fight against ground loop caused by cable TV connection, check the Fixing Cable-TV Hum in Audio Systems article by Jay Rose at http://www.tiac.net/users/jcrose/cablehum.html. Secrets of Home Theatre and High Fidelity web magazine reviewed an antenna wire ground loop isolator product UNHUMMER, so read the article if you are looking for an isolation device suitable for antenna network which is used in USA.
This circuit is a simple isolator for TV and Radio antenna connection. This circuit passes radio frequency signals nicely, but does not pass significantly 50 Hz signals, so the ground loop is eliminated. The circuit can be easily built into antenna connector or to a small box. I would recommend to use small metal box, where you connect one of the antenna connectors to the metal box and isolate other connector from box. Metal box allows mechanically strong contruction and provides good shielding against radio interference. The capacitors in the circuit should be rated at least 250VAC (400V DC) to make sure that the adapter with stands situation when antenna network ot television/radio is floating at mains live potential.
There is one disadvantage of this the circuit breaks the continuous shielding of the antenna cable which makes you antenna cable pick up radio interference more easily (for example radio interference picked by ground loop itself). Usually this is no big problem, but if you notice severe interference then you might have to stop using this isolator. The beast place tu put this isolator (to keep possibility of interference minimun) is just between TV receiver and antenna cable going to wall.
This capacitor isolator scheme might feel quite strange at the first sight, but it actually works and cuts the ground loop because it provides high impedance to low frequencies (50 or 60 Hz mains frequency) but has low impedance at the RF frequencies that are used at cable for TV channels. Capacitor isolator approach is an old trick used in TV industry. When the old TVs had their chassis at mains potential, they used this kind of approach to make sure that the dangerous voltage can get to the cable from the TV but the RF signal goes nicely to TV. Isolator used in one old TV had 330 pF 500 VAC capacitor which connects the center of the coaxial cable to tuner and the shield of the coaxial cable was connected to TV chassis through high voltage feedthrough capacitor (value unknown).
There is an alternative approach to antenna isolation problem: use transformer as in audio lines. The problem is to how to make a good transformer for antenna signals. If the transformer causes impedance mismaches, this can cause signal reflections which disturb you and maybe your neighbours also.
One way to do it is to use readily availabe 75 ohm to 300 ohm
transformers (called "baluns" or "matching transformers") used when
connecting old televisions with 300 ohm antenna input to modern antenna
network with 75 ohm connectors. Those units are readily available from TV
shops. Be sure to buy models which have no galvanic connection
between 75 ohm input and 300 ohm output (so there is isolation
between input and output), because some models only do impedance
matching but galvanic no isolation (they are useless in this project).
The circuit is easy to build. Just take two of those 75 to 300 ohm
antenna transformers and connect their 300 ohm sides together. Now
you have antenna isolator you need.
____________ ____________
__| |------X------| |__
75 Ohm |__ | 300 Ohm | __| 75 Ohm
|____________|------X------|____________|
This circuit has been suggested by Paul Grohe (grohe@galaxy.nsc.com), who
suggested that suitable transformers are available from Radio Shack
(Radio Shack cat. #'s 15-1140 and 15-1253 or MCM #33-050 and #33-010).
LiveDV magazine suggests using Radio Shack #15-1140 and #15-1523 antenna transformers wired together in their Soundings: Getting Wired tutorial.
If you experience radio interference picked by this circuit, you can
can try the following method to make shilding ogh the circuit better:
You can wrap the whole little assembly in aluminium foil and ground the
foil to the "cable" cable shield. But don't let it touch the other ground.
Aluminium Foil Shield
+--------------------------------+
| +--------+ +--------+
--Cable Co Coax-O----| Balun |======| Balun |-------- To TV
| +--------+ +--------+
+--------------------------------+
connect to shield of incoming coax
Video hum is low frequency noise from the ground lines which has influenced the video signal, causing degradation of the displayed signal. Usually observed as bars rolling vertically through the video image, video hum may also cause video distortion or even tearing of the picture in severe cases. Video hum may be a problem in any system where video sources and display devices are connected to different A/C power sources with varying grounding potentials.
Isolating video signal is more complicated than isolating audio or antenna signals, because the DC level of the video signal is important and video signals have very high frequency spectrum. This makes transformer isolation approach not possible.
Isolating video signal needs typically active technology which involves electro-optical isolation or differential amplifier (there are also passive Hum Suppressors). Electro-optical isolators convert video signal voltage to blinking LED and other part of the circuit receives that light and convert it to back video signal voltage. This method guarantees very good isolation, but has bandwidth and linearity problems. Poor bandwidth will result in fuzzy images and poor linearity will result in an inability to produce the same gain for all signal levels (most noticeable in gray-scale patters).
Differential amplifier approach uses an Operational Amplifier. Operational Amplifiers only amplify the difference between the two input lines. This method eliminates common mode noise between the incoming signals by making A-B=C, as only the difference between A & B are amplified. Operational Amplifiers is the only method to maintain wide bandwidth signals throughout your system while eliminating ground loop problems that are caused by power and video. Differential video amplifiers have a limitation on their input voltage range. If the ground potential difference is more than few volts, then operational amplifier based isolators don't work effectively. If you face this high potential differences, then you have definatly something wrong in the grounding of the building and you should consult a qualified electrician to correct this potentially dangerous problem.
Extron Electronics has a good article about video cabling ground loops th their web site. Read it for more information.
When you have two computers in different rooms connected together using long RS-232 wiring you can face ground loop problems. Isolating RS-232 line communications is harder than those audio or antenna connections. The best solution to solve those ground loop problem is to buy a commercial equipment which is designed for this kind of purposes. There are RS-232 isolators, current loop converters and short distance modems which can do the job. B&B Electronics has a very good data sheet collection (including schematics of many products) availabla on thei web site. They have also very good RS-422/485 and Current Loop application notes avaialble on their technical library. Protection of RS-232 Serial Connections tecnical bulletin from APC is worth to read.
Ground loops in Ethernet networks can cause network not to operate properly and other annoying ground loop problems.
The thick coaxial media system was the first media system specified in the original Ethernet standard of 1980. Today most sites use twisted-pair media for connections to the desktop. Thick coaxial segments are still sometimes installed as a backbone segment for interconnecting Ethernet hubs, since thick coaxial media provides a low-cost cable with good electrical shielding that can carry signals relatively long distances between hubs.
An Ethernet interface is attached to a thick Ethernet segment with an external MAU. The MAU provides an electrical connection to the thick Ethernet coax and transfers signals between the Ethernet interface and the network segment. The MAU is powered from the Ethernet interface, but all signal lines coming to the MAU are electrically isolated in the ethernet card.
The standard notes that the thick coax segment should be grounded at one point for electrical safety reasons. There must only be one grounding point, to avoid disrupting the Ethernet signals carried by the cable. All other metal parts on the cable should be insulated or carefully routed and fastened in place with plastic cable ties to avoid accidentally touching an electrical ground. If the components and cables conencted to MAY are properly isolated from nearly grounded metal parts, the system is ground loop problem free.
Thin Ethernet (10Base-2) uses coaxial cable which goes from computer to another. That cable should be grounded from one end for safety resons. That cable is electrically isolated from the computers at the ethernet card. The cable shield be accidentally and easily get in contact with the matal case of the computer if the metal connectors in the cable touch the matal case of the computer.
To avoid this kind of problems it is a good idea to use connectors which have plastick isolation over them or install a platic isolation around them. Make sure that the you don't have any metal connectors or broken cable shields connectors touching the metal wiring conduit.
10Bset-T Ethernet used twisted pair wiring and RJ-45 connectors. The wiring is completely transformer isolated in network card and HUB end. 10Base-T network wiring does not cause any ground loop problems. If you are working in enviroments where ground loops are very problematic then 10Base-T is a safe choice. It can cost a little bit more but is more flexible and you will save very much in long run in network trouble shooting costs.
It is sometimes suggested that an isolation transformer might be used to solve the ground loop problem. This will not work because all safety agencies require that the ground wire of an isolation transformer be passed through between the input and output (only the power wiring may be isolated). International office product safety regulations including IEC 950 and UL 1950 require that an isolation transformer is only allowed to isolate the hot and neutral wires; the grounding wire must be passed straight through. Since the computer circuits including data communication circuits are connected to the grounding wire and not the neutral wire, the isolation transformer or any power conditioner or UPS with an isolation transformer has absolutely no affect on computer grounding problems.
For laboratory use there is available special isolation transformers which also isolate the ground connection (at least in Finland). This tranformer provides complete isolation of live and neutral wires. The output can be non-grounded electricsl output because the tranformer provides adequate isolation. Remeber that you are allowed to connect only one equipment to this kind of safety isolation transformer. If you connect more that one equipments to safety isolation transformer, you create a potential hazard. This kind of transformer is good laboratory environment, but it might not considered safe or meeting the electric code outside laboratory.
Ground loops are not only a problem in connections between equipments. When you design electronics circuits you should always avoid causing unnecessary ground loop, because they cause many annoying problems. A typical problem when the grounding is not done properly is that the electrical noise from the noisy parts of the circuit gets to the parts of the circuit which should be free of noise. Here is some guidelines for designing grounding systems used in equipments:
When you have two circuits that are tied together electrically, but one of them is high current then you should direct the ground and power paths to "feed" them separately. You want the current of the driver to stay on the driver side and the current of the logic to stay on it's own side. The thin trace inbetween is still needed because this is not galvantic isolation.
e-> <-e |------------| |---------- | | | | <<<< physical CURRENT POWER FOR --REGULATOR LOGIC separation >>>> DRIVER DRIVERS | | | | | e-> | ground | <-e | -----|-------------------------------------------------------------- ^ thick ^ thin ^ traces traces very thick from reg to traces from logic load drivers to supplyThe common mistake is to "daisy chain" the ground by having the ground of the high current item seek it's current path through the ground of the logic. This causes ground spikes on the logic and thus logic errors due to bad voltage levels at the logic chips.
Physical separation is to prevent electromagnetic coupling, of course. Even getting the grounds proper won't help if you couple the magnetic field back into the logic traces.
Always image traces to be resistors. Thick ones are small resistance and thin ones are large. The objective in laying out the board is to encourage the large currents to take the path back to their own source without getting onto the other grounds.
Separating current paths in this way can make a micro run right along side of a vicious current driver and not have logic problems in most cases. The cases in which it usually doesn't work is when the signal being sent to the driver is analog instead of digital. You're going to get some amount of ground differiental with the separate ground paths and so the analog signal will reflect this differance in the signal voltage relative to ground.
Current loop coupling of the signal to the driver could solve a really bad problem of ground differientals, but I have never used that technique. If your going to go to that extreme then you may as well isolate them altogether.
If your signal is digital you can clean it up abit by having a schmidt trigger on the driver side of the loop with it's ground relative to the high current load. This can provide a volt or more of tolerance in the ground differance.
If you get the currents going right you will see less problems with the logic side, but you might see more problems with the driver because it's signal from the logic is corrupted by lifting of the ground potential because of the high currents. When you have reduced this effect by minimizing the high current ground ohmage to the point where you cann't minimize it any more AND you have included schimdt buffering, then it's time to admit defeat and galvanically isolate the two circuits.
When you have power electronics and some microelectronics on the same circuit the layout of the current loops is critical. This also applies to situations where you have microelectronics and audio circuit on the same board.