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Ground Loops
Alan Applegate (K0BG)
on
June 18, 2007
View comments about this article!
If there were but one bane in amateur radio, it would be the ground loop. Although they may appear in any type of installation, they're more often found in mobile ones. In any case, too many amateurs don't know what a ground loop is, or what causes them to occur. Even rarer, is the ability to recognize that a specific problem is caused by one.
The term Ground Loop in itself isn't very descriptive, but here's a stab at it with credit going to Mr. Webster: An unwanted electric current path in a circuit resulting in stray signals or interference, occurring, e.g., when two earthed points in the same circuit have different potentials. Please pay particular attention the last few words: ...when two earthed points in the same circuit have different potentials. Another way to look at this is, one is a better ground than the other. Or, one has a lower resistance path back to the power source; the battery in this case.
Mobile ground loops are most often seen when the requisite DC wiring is not properly connected. With respect to mobile radio installations, most vehicle manufacturers recommend that both leads (positive and negative) go directly to the battery. In this case, both leads need to be fused. At a minimum, the negative power cable lead should be tied to the same point as the main battery's negative connection to the chassis of the vehicle in question. Here, the negative lead of the power cable doesn't need to be fused.
If instead, you decide to connect the negative lead to the nearest chassis ground point (seat support, trunk brace, etc.), there will be a difference in resistance between any of these points and the battery's chassis ground. A differential of three to five ohms is not uncommon. Whether this causes a ground loop to occur is moot, the resulting voltage drop under load is not.
Digressing for a moment... Vehicle batteries have two standard negative leads. The main one (bigger of the two) goes directly to the starter motor housing, or very near it. The other lead (always smaller) is connected to the chassis of the vehicle. The former is to lessen the losses to the starter motor, the latter to provide a return for the various on-board electrical loads (headlights, accessories, etc.). Manufacturers really don't try to minimize the potential between them; their only concern is powering the various inherent and requisite devices.
Further, I don't want to get caught up in the argument about whether a mobile transceiver's ground lead should or should not be directly connected to the battery terminals, as there are pros and cons to each method. Suffice to say, the negative lead should be collocated close to the battery.
If I had to choose just one example of a ground loop, it would be the presents of alternator whine. Especially so when it only occurs, or predominantly occurs, in the transmitted signal. In some cases you can mask the whine by using a brute force filter in the positive lead. Besides the additional I2R losses incurred, it's a band-aid rather than a cure. While a bad or leaky diode may cause alternator whine to occur, the truth is, it's a very rare occurrence (nowadays).
In the whine cases I've been involved with, there are usually three common themes, alone or in combination. First, power is taken from the vehicle's wiring rather than directly from the battery. Two, the negative lead was connected to the nearest chassis ground point (seat frame for example) rather than directly to a battery ground. Three (and most common), the use of a mag mount antenna.
It should be apparent that direct battery connections should be made, at least the positive connection, as using existing vehicle wiring is fraught with problems. This includes the use of Accessory Power sockets as neither the wire size nor the fusing are adequate for any HF radio. Adding insult, there are devices marketed which supposedly circumvent the inherent problems associated with using them; a incredulous advertising ploy with no merit!
If it makes you warm and fuzzy connecting the negative lead to the battery chassis connection, rather than to the negative battery connector itself, great! But don't use seat rails and other metal body parts unless you want to invite problems.
If you're using a mag mount antenna, and you have whine on your transmitted signal, try this. Replace the antenna with a dummy load. If you can still hear the whine on a near-by receiver, the problem is in the DC wiring, or the alternator (albeit doubtful). If you can no longer hear the whine, then ditch the mag mount and drill the necessary hole.
I have always been in favor of common grounds, and common power supply points. Doing so, lessens the possibilities for ground loops. One way to do this is to use a RigRunner or similar common connection device. If you do use one, you won't need the fuses which came preinstalled on your transceiver's power cable. In fact, you're better off shortening the cable (less I2R losses) rather than bundling it up with a tyrap. Just remember, the RigRunner's power cable needs to be fused very close to the battery connection points.
Some amateurs tend to go crazy installing DC grounds on every single piece of installed gear as if God commanded it so. One common practice is to ground the transceiver's chassis to the nearest hard point. If this cured a problem (ground loop or RFI related), then something else in your installation was amiss, and it's usually a poor coax connection or ground plane issue.
It's assumed that most vehicle manufacturers scatter ground connections hither and yon throughout the vehicle. That is not the case. While there are multiple ground connections made, the same ground points are used for any given sub-assembly. For example, there are no separate grounding points for each headlight. Indeed, they're common. Another way to look at this is, if power for more than one device comes from the same supply point (relay, switch, battery, etc.), then the grounds for those devices should also be common. In case you missed the point, this is to lessen any potential for a ground loop (pun intended).
If you cause a potential to appear between two factory ground points (e.g., ground lead to a seat frame, positive lead to the battery), the resulting ground loop may manifest itself as an RFI problem. This is especially important when high currents are involved (amplifier use for example). Split beads, brute force filters, and ground straps ad nauseam, won't cure the apparent RFI simply because RFI is not the cause!
The most important point that can be made in preventing ground loops is to use correct wiring practices. Not only are direct battery connections necessary, adequate sized conductors and fuses are also required. The truth is, most factory supplied mobile transceiver power cables are barely adequate for the load. Extending them just adds insult to injury, unless you're using a RigRunner or other device equipped with over-sized cabling.
It seems, no matter how many times a myth is dispelled, they keep raising their ugly head. One common myth is that power cable fuses protect the radio from damage. They don't. Myth number two is, that a fuse will open instantly as soon as the current exceeds the fuse's rating. They won't. Myth number three is, it's always okay to use fuses designed for 120 volts AC, in a nominal 12 volt DC system. It isn't.
The first truth is, fuses are there to protect the cabling. For example, the Icom IC-7000 has a 5 amp (system) fuse mounted inside the radio, and 30 amp fuses in the cabling (plus and minus). If you short out a supply connection (pin 3 of the tuner port for example), a circuit board trace and/or switching transistor will fail long before the 5 amp fuse opens. The 30 amp fuses will never open in this particular case. It can be argued that the power cable fuses do protect the radio if something fails catastrophically, a final perhaps, but chances are some other component in the circuitry will be damaged beyond repair before the power cable fuse(s) opens.
The second truth is, all fuses exhibit hysteresis. This is the time lag between any given ampere overload and when the fuse opens. For example, a nominal 20 amp fuse will handle a 30 amp load for about 90 seconds. It will hold a 100 amp load for about 1 second. This is one reason slow blow fuses are not recommended for amateur devices.
So, if the radio draws just 20 amps peak, why not use a 20 amp fuse instead? Here's why. Subjecting any given fuse to instantaneous loads close to their current rating will eventually cause them to fail due to element fatigue (sometimes referred to as erosion). Depending on the load characteristics (steady or varying), fuses are sized from 25% to 50% larger than their impressed loads.
Digressing again... In some cases, peak loads will exceed the rating of the fuse, like those encountered when starting an electric motor. Depending on the application, the designer may use a slow-blow fuse with an appropriately longer hysteresis rating. However, in an amateur application, it is only necessary to keep the average current draw below about 60% of the rating for any given fuse to avoid element fatigue. However, the correct wire size should be based on the peak current, not the average, if you want to keep I2R losses low. In any case, should a dead short occur, the wire size needs to be large enough to carry the current imposed by the fuse's hysteresis time delay without exceeding the wire's temperature rating. After all, you don't want to turn the wire itself into a fuse!
As stated, part of the sizing calculation is the temperature rating the protected wire is designed for, as well as its ambient operating conditions. In other words, the fuse must open before the wire reaches its maximum rating for any given overload. Incidentally, underhood wiring should have a temperature rating of at least 90C, and preferably 105C.
The third truth is, all fuses elements have resistance, and when the current flows through them, they heat up. The elements are designed to melt at a specific temperature thus protecting the wire, and to a lesser the equipment connected to the wire. For any given ampere rating, fuses designed for high voltage (nominal 250 volts maximum) service typically have lower resistance than those designed for low voltage (nominally 32 volts maximum). Thus, their low voltage hysteresis time is elongated, which means they take longer to open under a given overload.
Further, fuses designed for AC service typically have longer arc paths and may be filled with arc suppressing material. While these facts alone don't preclude their use in low voltage applications, here too the hysteresis time delay may be extended. The bottom line is, you should select fuses specifically designed for the voltage range in use.
What ever you do, don't buy cheap fuses. Both Littelfuse and Bussmann manufacture high-quality fuses with consistent hysteresis ratings. Some off-shore types act more like a shorting bar than a fuse. That is to say, forewarned, is forearmed!
Do mobile radio correctly, and you can have a lot of fun. Do it wrong, and it can become your main bane!
Alan, KØBG
www.k0bg.com
This article has expired. No more comments may be added.
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Ground Loops
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by KA9DTZ on June 18, 2007
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Great article Alan. It might also be mentioned that frequencies as low a 10 kHz begin to act like RF given multiple ground paths. Given that fact, it only becomes more important, and generally more difficult, to ensure a low impedance ground path for RF circuits.
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RE: Ground Loops
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by W6TH on June 18, 2007
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.
Great and useful article Alan. Now you and I agree and satisfied my findings as to why my fuse holder gets warm/hot.
.:
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RE: Ground Loops
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by K3AN on June 18, 2007
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Alan, are you saying that a 10 Amp fuse rated for 250 Volt service will take longer to blow from a 20 Amp flow of current than a 10 Amp, 32 Volt fuse will? How much of a time difference is there? Can you provide any on-line references?
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Ground Loops
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by WW5AA on June 18, 2007
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Alan,
If everyone doing a mobile installation went to your web site, there would be very little activity on this forum. Thanks for all the great work and help!
73, de Lindy
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RE: Ground Loops
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by K0BG on June 18, 2007
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Bill, go to www.littelfuse.com. You'll need to search for the specific fuse by type. The Spec sheets are .pdf files. Depending on the fuses you are comparing, the hysteresis delay increases from 5% to as much as 50%.
Alan, KØBG
www.k0bg.com
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RE: Ground Loops
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by K5LXP on June 18, 2007
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I've experienced just the opposite situation with regards to mag mount antennas, where there was no alternator whine with a mag mount, and it appeared once a permanent antenna was installed. The mag mount doesn't offer a DC path to ground since it's insulated from the vehicle via it's plastic base and/or the paint of the vehicle. When a permanent antenna is connected, the ground path through the coax braid is established. Indeed, the problem is a ground loop through the coax shield, which didn't exist with the DC-isolated mag mount. I'm in the camp where you ground the rig to the chassis nearby, but not sharing the same chassis ground point as the battery. Then no matter what happens to the battery ground and under-hood connections, ground currents won't find your radio a better path. Fewer burned up radios that way, in my experience.
Mark K5LXP
Albuquerque, NM
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RE: Ground Loops
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by WA1WIG on June 18, 2007
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This is always an interesting topic and often misunderstood.
A note "Another way to look at this is, one is a better ground than the other." is not really correct, it should end with the grounds are "different from each other". In most practice, the "ground" really means just a common reference, not "earth".
Ground loops are also impossible to avoid! In many mobile scenarios, with a mounted antenna, there will be a connection to the common reference (car body) via DC power and antenna shield at the mount. Add a ground to the rig and there will be at least three connections to "ground".
In general, the car body (if metal) is the reference and given it's very large surface area, usually is a solid RF reference element.
The wire from the battery to car body is usually short but the negative rig wire is usually both long and of significant RF impedance due to skin effect.
Solving problems is an art! Sometimes it is wise to and a series filter/choke to both the positive and negative power lines and either just use the coax shield as an RF/noise ground or bond the rig to the car body.
In any installation, base or mobile, sometimes it is best to interrupt the RF/noise continuity of some grounds that can not be made short! The choke/filter need only be effective at the frequencies causing problems.
In most cases, establishing a plane as ground reference is of an advantage. It might be a car body or sheet copper in the shack. I have worked on one extreme, a building with a 1/4" solid plate (welded seams) spanning the entire facilities floor!
73 de WA1WIG
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Ground Loops
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by KC8QFP on June 18, 2007
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I like to have ONE pathway to earth/ground, thus no "loops". One ground BUS from all the RF equiptment, and then that goes to the ground rod. But with three pronged plugs, you can have multiple pathways to ground, and this could mean problems related to loops. One mistake that I've seen is when people "chain" their stuff, one to the next, rig to rig, to tuner, to switchbox to dummy load etc etc etc in a long line, then end all that with a ground connection. IF any of the stuff is also grounded via the coax/antenna, three pronged plugs, and so on, you got loops. I feel it is much better to have everything go to one long bussbar, and then only ONE path from that to ground. The tricky part is properly grounding antennaes. And I also feel that it is better to go too big than too little when it comes to conductors. Braided cable is nice for this purpose.
From my experiances with cars, I've found that many malfunctions and car troubles have to do with poor chassis connections. If corrosion gets into the connectors, or rust on the body (especially around chassis connections), this will make a mechanic some money, when all that is needed is to clean connections to bring it back. I've seen many car computers go nuts since they reply on resistance readings for some of their functions (O2 sensors are notorious for this malfunction). So corrosion is a major cause of car troubles. The heavy cable from BATT POS to engine block is the main chassis connection, BUT there is a ground strap (braided cable or heavy wire) that also goes from the engine to the chassis frame of the car. Cables go bad, grease/oil and corrosion can often make this vital chassis connection go bad. Many people do not know about this engine to chassis cable, it's usually less than a foot long. Loose connections are more of a problem than ground loops in a car, I kind of think of the car chassis as one large BUS IF all the connecitons are good and tight. The same goes for external connections as you'd find on your tower, antenna, lightening arrestors, baluns etc. Good clean solid connections are very important when considering ground loops.
73! Don
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RE: Ground Loops
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by K4JSR on June 18, 2007
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Another timely and informative article, Alan.
I hope this will put us all on "Common Ground".
You are certainly most wise in also including the information about fuses. Most of us never really think that there could be so much difference in similarly rated fuses.
The things you have preached about on good mobile radio installation seem to have been forgotten by the masses. This seems to be the day when most hams go to
their friendly local ham store for technical advice and tend to ignore good technical articles or books.
Just goes to show that instant gratification is indeed the quick path to frustration and failure.
Even though I've been an active ham since 19-ought-54,
I would not think of installing a mobile radio without consulting your website and Tom, W8JI's before
getting the tools out.
Is it just me or has anyone else noticed the lack of
technical forums at hamfests? There is a hunger for
knowledge out there. Unfortunately many of our clubs and hamfest organizers are failing to fill the niche.
Far too many new hams rely on places like this for their instant gratification and doing so without even bothering to check and see if their inquiry has been previously covered.
Thanks again, Alan. You also managed to get a positive comment from Chip, W1YW!! ;-D
73, Cal K4JSR
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RE: Ground Loops
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by WA1WIG on June 18, 2007
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>>> From my experiances with cars, I've found that many malfunctions and car troubles have to do with poor chassis connections.
Very true. The body/frame is usually bonded very well but many connections to it are not! The main article mentioned not to use mounting bolts such as seat mounts. They were never designed for electrical performance, often have paint or corrosion.
With a welded metallic body, the body is by far the best reference "ground" in the vehicle. It is connections to it that are the problem.
On a different note, I didn't see an explanation of why rig manufaturers recommend direct connection of the negative power to the battery with a fuse. The fuse is unrelated to noise, too many rigs were fried by a intermittent in the car's battery-chassis ground. In this case the rig's other "grounds" such as antenna shield end up as the only path from battery to chassis and negative side electrical wiring.
73 WA1WIG
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Ground Loops
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by K1CJS on June 18, 2007
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Good reminders and a great article!
There are disagreements about some of the methods used, where ground connections should be made and other things, but Alan has made clear what the drawbacks are. For one--ground loops can be avoided by making sure bonding is complete--if the difference in potential between parts of the auto body is zero, no matter how many different paths there are there is no ground loop.
Thanks Alan and keep up the good work!
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RE: Ground Loops
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by WA1WIG on June 18, 2007
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>>>One common myth is that power cable fuses protect the radio from damage.
The negative fuse IS intended to prevent damage to the radio!!!
Already mentioned in another reply but this needs it's own comment.
The fuse in the negative lead protects the rig from a nasty situation where the battery negative lead is disconnected from chassis/negative power distribution. This can be very brief due to shock of vibration.
In such a case, the negative lead will be the only DC power connection for the vehicle! The rig's negative DC power line is bonded to the rig's chassis. The antenna shield is also bonded to the rig's chassis and very often the coax shield is bonded to the chassis at the antenna mount.
Even a brief interruption of the battery to chassis/DC distribution connection without the rig fuse will fry a rig if the antenna coax shield is bonded/contacting the body!
72 de waiwig
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RE: Ground Loops
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by K0BG on June 18, 2007
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Gerry, while I agree with you, I wonder if that is really the case. If you look inside an IC7000, or IC706 (I'm sure most others are no different), the wires attached to the chassis mounted power plug are routed to the circuit board through rather small wires. I suspect if the case you present happens, the circuit board or the interconnect wires will fail before the fuse opens.
Alan, KØBG
www.k0bg.com
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RE: Ground Loops
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by W3WW on June 18, 2007
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Alan,
Excellent article.
Now, I need to go re-wire my ground system. I probably have a ground loop, which explains my strange keyer speed shifts. Thought it was my K3, so I bought another and.......same problem.
Thanks again,
Don
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RE: Ground Loops
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by K8MHZ on June 18, 2007
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Alan,
As an electrician of many years I applaud both your understanding of the physical characteristics of fuses and your effort to explain rather complex situations in an easy to understand manner.
Thanks!
73
Mark K8MHZ
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RE: Ground Loops
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by W9PMZ on June 18, 2007
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Nice article on ground loops Alan, very informativie. Also good information on fuses. Fusing always seems to be a hot topic for electronic products when they start blowing in new product introduction.
Regarding,
"What ever you do, don't buy cheap fuses. Both Littelfuse and Bussmann manufacture high-quality fuses with consistent hysteresis ratings. Some off-shore types act more like a shorting bar than a fuse. That is to say, forewarned, is forearmed!"
Fuses are a comodity. I'd be suprised if they were made in the USA. See the manufacturing locations from Bussmann's web site below:
"Manufacturing Facilities
Globally, Cooper Bussmann operates 12 manufacturing facilities. They include:
Asia
Dongguan, China
Hong Kong, China
Shanghai, China
Pondicherry, India
Seoul, South Korea
Europe
Burton-on-the-Wolds, England, UK
Copenhagen, Denmark
North America
Dublin, California, USA
El Paso, Texas, USA
Goldsboro, North Carolina, USA
St. Louis, Missouri, USA
South America
Ito, Brazil "
A cheap item, like a fuse, will be made in the lowest cost region from the above list. If it is the USA, look to El Pase.......
73,
Carl - W9PMZ
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RE: Ground Loops
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by K5LXP on June 18, 2007
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In several instances where I've found ground loop issues the fault wasn't severe enough to blow any fuses or damage internal wiring but manifested itself in other "wierdness", like alternator whine coming out of the speaker while the radio was turned off, or the radio getting hot without transmitting. I have yet to see a conclusive reason why grounding the radio to the battery terminal is better than 1" away from it's chassis connection point.
Mark K5LXP
Albuquerque, NM
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Ground Loops
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by WA1RNE on June 18, 2007
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" At a minimum, the negative power cable lead should be tied to the same point as the main battery's negative connection to the chassis of the vehicle in question. Here, the negative lead of the power cable doesn't need to be fused.
If instead, you decide to connect the negative lead to the nearest chassis ground point (seat support, trunk brace, etc.), there will be a difference in resistance between any of these points and the battery's chassis ground. A differential of three to five ohms is not uncommon. Whether this causes a ground loop to occur is moot, the resulting voltage drop under load is not."
>> Alan, a good informative article but I have a couple of comments and suggestions:
Although maintaining a single point ground scheme is desirable to reduce ground loops, I'm not sure I would push this advice too hard given the challenge of doing so in most vehicles.
The high current battery return usually terminates at the engine block with a large bolt - and often in a place that is not easily accessible. Messing around with this connection to install a radio or other accessory is not desirable, considering that it handles hundreds of amperes for starting the vehicle and it's electrical integrity needs to be kept intact.
After the vehicle is started, this cable serves as a very low impedance interconnect between the battery and chassis, and is much easier to access than the opposite end at the engine block - thus the reason this connection is often recommended. The positive terminal is obviously within 10 inches of the negative completing the power connection.
If you use a nearby chassis ground point you should be safe since a frame and chassis in good condition should only create a series resistance in the single digit milliohm range. If you have 3-5 OHMS of resistance between any chassis ground and the battery/engine "mecca", it would take only 2.4 amperes to drop the battery voltage to zero - indicating there's an unusual problem with that chassis connection- like rust or paint between surfaces or something worse. A seat frame might have paint between it and the chassis, but I'm not sure why anyone would consider using a seat frame to ground a radio.
...WA1RNE
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Ground Loops
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by W1YW on June 18, 2007
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Chip you have been most congenial lately.
------------------
Some of the content on e-ham has been very good to excellent lately. Or at least useful and informed starting points for discussion.
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RE: Ground Loops
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by WA1WIG on June 18, 2007
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Alan,
Actually I worded it poorly :( The negative power is usually connected to the circuit board ground. The circuit board ground is connected to the case via the antenna shield if nothing else. This is at DC, there sometimes are some filter components on the DC input as well.
"Bonded" was a poor choice of words. It is actually worse as you stated! Connected via circuit board. I have actually seen fried main boards due to this on comercial gear.
73 de gerry,
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RE: Ground Loops
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by W6TH on June 18, 2007
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.
I run all power to my rig directly from the battery and neglect the chassis ground. When hooked as mentioned, my negative power lead, black fuse block going to the radio runs hot at full power for long period of transmitting time, the red lead is cool; this is normal. The shortest lead to ground runs from the battery minus to the block. The antenna is a different story; I have a rear hitch to the chassis ground for hauling a trailer, this is my only separate ground and is my counterpoise or the other half of my antenna system configuration.
For fuses, the BUSS fuses are made in the USA, the LITTELFUSE INC., are made in Mexico. The fuses I just purchased from Wal-Mart are an exact duplicate of FUJI fuses that came with my four radio transceivers. I stocked up with the 20, 8, and 5 amp fuses.
P.S. I changed the fuse blocks to a better made, bought at Wal-Mart and is for automobile use and no longer run hot.
.:
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RE: Ground Loops
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by N6AJR on June 18, 2007
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Nice article, I like to do good grounds, I don't know if they help a lot but I do 2 starter cables ( from the autoparts store) about 6 bucks each and can carry 300-400 amps, with the fklattened ends with the hole in them.
I fuse both sides , and run the neg side to a bolt theough the floor boards on the passenger side up above the carpet. this grounds the battery to the chassis and grounds the neg side of the radio to both the battery and chassis ground.
I run the pos cable through a grommet in the firewall and then bolt all of my Pos leads to this then tape it with scotch 33, then put it in a small tupperware container and tape it again and shove the whole mess up under the dash.
along with the radio power, in my truck I als power a 800/1600 watt inverter ( for coffee when mountain topping) that also charges the logging laptop.
I also run a strap from the neg battery post to a fender washer bolt near the battery,
I run a ground strap from the case of the radio to the floor close to it eith more brwaid and a self tapping sheet metal screw with star washer.
my antenna is on a diamond K 400 C mount and I run a braid from the shield side of the mount to a bolt on the car side of the trunk hinge, again with a star washer.
I have always done them this way, and it works for me, I don't think a good ground is a magit elixer, but they do need to be inplace for most stuff to weork as adverised
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RE: Ground Loops
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by WI7B on June 18, 2007
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"With respect to mobile radio installations, most vehicle manufacturers recommend that both leads (positive and negative) go directly to the battery."
--K0BG
Actually, this is not true. It is dependent on a number of factors in the electronics and modular design of the vehicle. Even for one manufactor (e.g., GM) it may even depend on the specific model of car.
See...
"Radio Telephone / Mobile Radio
Installation Guidelines" - GMNC
=> http://service.gm.com/techlineinfo/radio.html
"5. Radio Wiring and Connection Locations
A. Connecting radio power on General Motors vehicles is model dependent. The installer must decide which one of the following four methods will be appropriate.
1.) Connect the positive and negative leads directly to the battery terminals (illustrated in this guideline).
2.) Connect the positive lead to the auxiliary power terminal (located at the underhood fuse center or identified by a red plastic cover in the underhood area) and connect the negative lead directly to the negative battery terminal.
3.) Connect the positive lead to the auxiliary power terminal and connect the negative lead to the battery body connection point (identified by a short #10 AWG or larger wire running from the negative battery terminal to the body of the vehicle).
4.) Connect the positive and negative leads to the Special Equipment Option (SEO) wiring provided for this purpose."
73,
---* Ken
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RE: Ground Loops
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by AA4PB on June 18, 2007
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Having multiple grounds on the typical radio installation is difficult to avoid on a permanent basis. On my IC706MkIIg installation for example, the VHF/UHF antenna is grounded, the HF antenna tuner is grounded, the radio is grounded to the dash via the metal mount, and the radio is grounded near by the battery connection via the power cable. Thats a total of four widely separated grounding points.
The key is probably to make the primary ground (the power cable) as direct and low impedance as possible. The multiple grounds can still cause problems like alternator whine with some radio designs. I had an Alinco that had the negative power lead connected to the printed circuit in such a manner that it routed alternator noise right into the receiver audio circuits. The solution in that situation turned out to be adding a heavy wire between the heat sink and the negative power lead to provide a low impedance path around the printed circuit board.
Using the best standard practices minimizes problems but sometimes you still have to track down the source of the "ground loop" and devise your own solution.
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RE: Ground Loops
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by KC6TOA on June 18, 2007
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Once again K0BG show us his superior knowledge, thanks.
Just like people confuse DC grounds and RF grounds, there can be confusion between DC ground loops and RF ground loops.
When somebody mentions "impedance", to me that says they are talking about RF. DC has no reactive component.
Connecting your radios DC power wires directly to your battery provides a low resistance path. It has nothing to do with RF. (i hope there is no RF on these wires)
Your vehicle's chassis acting as the ground plane for your antenna is where the RF ground and chassis (low!) impedance properties are important.
Lastly, the unfortunate fact is that our vehicle chassis isn't even on earth ground. The last time i checked, rubber tires don't conduct electrons very well.
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RE: Ground Loops
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by RADIOGUYR2 on June 18, 2007
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Alan:
Too many fuses can be bad too. I noticed that you didn't go into the IR drop across a fuse which is what really makes it blow, or in this case burn open.
While it is important to have a common ground at one point to keep the ground loops down it is also important to use the proper wire size to the fuse so as not to have the IR drop occur in the wire instead of the fuse. Then again. Most of the radio manufactures that have nice heavy wires (bigger than No. 10) make sure the ratio is above the 2:1 limit on current. To undercut the ratio one then could have the wire develope the drop and in turn act like the fuse, heating up, all while the fuse is just sitting their and not doing its job.
Grounds are important, including the antennas return ground to the radio (don't use the coax for the radio return ground from the antenna. Insure the car body or seperate lead from the antenna back to the radio is conductive at the highest band. remember the coax can create a ground loop too) One also should note that the ground strap must have the same cross sectional area as one finds in a No. 8 or 6 wire. Ground strapping is noted for having problems with age.
However, one also needs to have the proper gauge of wire (2x current draw... length dependent on voltage drop) to have the fuse work properly and not entertain a IR drop so that the voltage at the radio (max output of the radio) is causing a pulldown (IR drop) in the line going to it.
Some have actually gone to using dual power wires and dual ground wires to help reduce the IR drop as well as helping to eleminate some of the induction noise that a single wire does.
A good choice in vehicles is also to put in a master relay from the battery to the radios. This is mainly due to the fact that almost all ham radios have the finals hot all the time (connected to the battery) So that when you twist the key to start and get all the spikeing created by the starter motor and surge when the alternator comes on line it won't appear to the final transistors of your radio.
By using a vehicle master selonoid you can keep this from causing damage to the radio as well as not having a dead battery due to a final leaking. Most of the ones we use are of the 85 amp versions or higher, again so the IR drop is not occuring at the connector.
some get creative and hook it up to the key circuit, thus when you start the engine the selo is off line, once the engine starts then it makes contact. Others just perfer to use a small toggle switch to manually turn it on or off.
On wire, one does not want to use the fancy red and black (speaker)combind wire. I know that it looks the same as the icom or others, but its not. It has a lower melt temp that has been responsible for severl vehicles catching on fire. Here we perfer using the best one can get. Aircraft grade doubble insulated wire from the local avionics shop is well worth the extra money when you go to install the radio in the vehicle. It not only is better insulated but its also a better grade of wire plated so as to reduce the contact IR drops.
Good article Alan. always a pleasure to read your latest.
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RE: Ground Loops
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by AA4PB on June 18, 2007
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When somebody mentions "impedance", to me that says they are talking about RF
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Impedance is not necessarily related only to "RF". It can be related to any AC signal, including audio frequencies. I use the term "low impedance" when talking about the power line because it relates to minimizing the alternator whine which is an AC signal in the audio range.
It is possible to have a very low DC resistance and still have a relatively high inductive reactance to alternator whine and other "noise". Saying "low impedance" implies low DC resistance as well as low reactance to low frequency AC signals. Low impedance covers it all while low resistance covers only the DC properties.
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RE: Ground Loops
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by AA4PB on June 18, 2007
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A good choice in vehicles is also to put in a master relay from the battery to the radios
----------------------------------------------------
This depends on the design of the particular radio. I've had radios with large filter capacitors (> 1000 mFd) in the power circuit. When I had a relay removing power, the slope of the discharge on the capacitors occassionally caused the processor to reset and clear all of the memories. I cured the problem by keeping DC power applied to the radio at all times and turning it on and off with the front panel power button.
Most of the newer AM/FM radios in vehicles use constant power to the radio circuits. The accessory line is only a "sense" line to activate a power switch inside the radio to activate the low power circuits. The power amplifiers have DC power applied at all times.
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RE: Ground Loops
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by W4LGH on June 18, 2007
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Ground loops can be nasty, and cause all sorts of problems, especially with RF. They can be very HARD to find, and sometimes even harder to fix!
One common problem with ground loops in home installations is a difference in your house ground, and your external ground that you put in for your radios. This is less of a problem today, with 12VDC radios, but was a real pain before the day of 3 pin AC plugs, and AC operated radios. Also running long ground wires will result in weird things happening as well, as a 30' ground wire is almost 40meters!
The term "ground" is really a bad word to use when dealing with AC or RF, as you can only ground one frequency. I have always prefered to call it a "common" rather than "ground" as common better describes what is really happening. (ie: tying everything to a common point)
Being an old Vintage radio guy, I have to be real careful making sure there are no "LOOPS" in my shack!
73 de W4LGH - Alan
http://www.w4lgh.com
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Ground Loops
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by AI2IA on June 18, 2007
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Common sense! Common sense! If you do the installation slowly and carefully, paying attention to the location of rigs and wires, if you keep shields intact, if you ground cases and watch where you run leads, you can forget about ground loops. A sloppy installation is an invitation for hours of troubleshooting.
Do it right, or do it over, and over and over.
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Ground Loops
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by WA8MEA on June 18, 2007
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After almost 40 years in ham radio, I'm about to coin the phrase "grounding theory" to go along with the term "antenna theory".
Why? Because after all of the stuff I've read, and all of the stuff I've experimented with over the years, NOTHING is as it seems!
I have NEVER grounded every rig/accessory in the shack to a common ground point. Why? Because there is always another ground path that might cause a loop to develop. For example, take your power supply. It takes a ground path via the AC wall outlet. If you are using a vertical antenna with a mast pipe resting on the Earth, you've got another loop.
I recall connecting a power supply to a new Yaesu rig years ago. I tried everything to stop the dam RF! Grounding everything, ungrounding everything, grounding certain things, grounding uncertain things. The ONLY thing that stopped the RF was switching to a car battery!
To me, grounding is a crap shoot. Depends on your rig, your antenna and any accessories.
73, Bill - WA8MEA
http://HamRadioFun.com
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Ground Loops
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by AI2IA on June 18, 2007
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In contrast to the above comment, in my shack every single piece of equipment with a metal cabinet is grounded by its own short ground strap to a common ground bus connected to electrical and earth ground.
I have no RF hot spots, hot mikes, RF into my audio, or any other problems. Everything is quiet aside from working as it should work. I also have the satisfaction of knowing that if any hot lead anywhere shorts to an equipment case, it will blow a fuse or pop a circuit breaker. I check all connections from time to time to make certain that all is as it should be, and yes indeed I keep a fire extinguisher within arms reach. Nothing is powered on unless I am there, and everything is powered off when I'm gone. For me, this is the only way to go.
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Ground Loops
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by N0AH on June 18, 2007
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I checked with the ARRL about my ambient noise on my radio. Per vehicle type, they records of various components causing RFI. In my case on my 1996 Ford Pick-Up, the fuel pumps inside the dual tanks had been recalled for causing noise on stereo equipment.
Since the recall had expired, I inquired on dropping the tanks and replacing the fuel pumps- $800-
I just went out and ground strapped everything I owned on the truck. The biggest noise killer was when we ran ground cables from the engine block to the chasse. We only ran 3/4 inch x 12 inch high quality straps. They are covered in plastic housing.
As Alan has suggested before, I used ground straps on the exhaust system. I used ground straps from the frame to the chasse in several areas. I also ran a ground strap from the hood to the chasse.
We used 14 in all. I used to get 4-5 s-units of noise when I started the truck. Now I get about 1/2 of an s-unit. Really amazing stuff. t has given me a whole new perspective on DX listening to UA0 signals over the pole.
The internet is so full of mobile RFI pages....most are C.B. related, some amateur radio. Some make sense, some don't. Stick with Alan.......
BTW, using a Yaesu FT-900 and a Tarheel series 100 antenna. Using my 259B analyzer, the system looks great!
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RE: Ground Loops
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by W4LGH on June 19, 2007
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Actually everything works as it should, but nothing works as it is perceived or understood! Grounds or Commons are necessary, but much care MUST be used in keeping the paths the same.
2 paths at different potentials, and you'll get a loop every time! A little pre-planning will go a long way.
73 de W4LGH - Alan
http://www.w4lgh.com
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Ground Loops
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by W4VR on June 19, 2007
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Thanks for the excellent article. We need more articles such as this one to educate some of our newbies and old-timers alike on the merits of following proper technical guidance in the construction of an amateur radio station, whether it be fixed or mobile. Lately, too many articles have been written on this website that offer inaccurate information or are so poorly written it's hard to make heads or tails out of what the author is trying to convey to readers.
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RE: Ground Loops
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by NS5M on June 19, 2007
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KC6TOA: "Lastly, the unfortunate fact is that our vehicle chassis isn't even on earth ground. The last time i checked, rubber tires don't conduct electrons very well."
I recall reading somewhere (please don't hold my feet to the fire) that because tires are no longer made of pure rubber, the carbon in them does indeed create a path to earth-ground. Now I have to wonder if the steel-belts and carbon body (or carcass) set up some kind of a capacitor ...
This has been an interesting thread - my thanks to Alan and all contributors.
73,
Jim
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RE: Ground Loops
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by K1CJS on June 19, 2007
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WI7B wrote:
"("With respect to mobile radio installations, most vehicle manufacturers recommend that both leads (positive and negative) go directly to the battery."
--K0BG)
Actually, this is not true. It is dependent on a number of factors in the electronics and modular design of the vehicle. Even for one manufactor (e.g., GM) it may even depend on the specific model of car."
The vehicle manufacturers do not take into account the amperage draw of ham transceivers. After all, ham radio type installations comprise such a small percentage of the after market auto installation picture. What isn't realized is that typical auto wiring just won't supply the optimum voltage and current for most HF transceivers to operate. That is why the first option you quoted IS the first option--it is really the only option.
In the commercial Motorola radios of not too long ago--the 'works in a drawer' type mounted in the trunk with a control head in the vehicle, the wiring harness incorporated a 20 foot length of both black and red power wires which were at least #10 gauge--sometimes #8. These wires were to run directly to the battery and each one had a fuse holder inline. This was the main power feed to the transceiver--a transistorized unit, not tubed.
The installation instructions stated in no uncertain terms that to safeguard the radio and provide optimum radio performance the connection must be made to the battery and nowhere else.
I figure there must be a method to their madness, so I recommend doing it this way to my friends when I install their equipment. After I explain the reasons and the benefits, most see it my way. Those that don't I politely tell to have their installation done elsewhere.
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Ground Loops
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by W6UEE on June 20, 2007
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Alan;As you may notice, I know just about everything but maybe Im a little rusty on some things and ground loops is it!!! I have a 2001 Jeep and I'm just about to my wits end.I am trying to instal an Alinco DR-590 Dual band transciever. The problem is yhat when I turn on the headlights either the computer (in the car)or some other culpret causes a signal of about 1600 cps to be transmitted by my unit. I have cleaned up the altinator whine by building the whine filter described in the last couple of issues of QST.The rig is quiet alt but I can't kill that blasted 1,6 Kc tone and it is quite anoying to anyone listening. Can you offer any advise? Thanks a lot. By the by,I'm running the remote head on the dash. Del
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Ground Loops
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by K4TAX on June 24, 2007
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Over the years I've found that the subject of grounding is one of the least likely understood topics among hams, new and old, today. The article on mobile grounding is very good, very well written and well thought out. Some of it applies to stations at home as well.
The point is made that any two or more points connected to "ground" will be at different potentials in as much as there is some value of resistance between the two points. Thus ground is not really ground. I think that "common" is a more correct term if I may use the term and phrase. Keeping these common points connected in such a manner so as to have the lowest resistance path should be the objective. In a mobile, the massive vehicle body is a start. Connecting the electrical system to the vehicle such that all share a common point is the objective. Just remember, low resistance wins.
In place of fuses, explore fast acting magnetic circuit breakers. They are more predictable, do not rely on temperature to operate and have a much less and thus a constant IR loss. Unfortunately, they are more costly and physically larger than fuses.
Operationally, fuses placed under the hood can go from a minus termperature value in winter to a 200+ degree temperature in the summer. The tolerance in amps based on when they let loose can be widely varied. As the temperature increases the current carrying ability decreases. A fuse that blows under high heat in summer might be replaced with a larger value to maintain service. Then comes winter and the fuse would be over-rated for proper load protection under lower temperatures.
Great article, please re-read it and do put a fuse in the negative lead to your radio.
73
Bob, K4TAX
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