A Primer On Grounding for Hams

A Compilation Of Information On RF and Safety Grounds

Nothing like a fierce electrical storm to get Hams talking about susceptibility to lightning strikes. Well, we experienced just such a storm in early August, which provides the perfect opportunity to review the topic.

Proper grounding of radio stations is probably one of the least understood aspects of  ham radio.  It almost has a certain aura of mystique or magic about it instead of being the pure science it should be. This is a very important aspect of any radio installation. There are two major criteria we need to consider when doing the planning for this installation. The primary reason has to be safety, both for ourselves as the operator who will be seated at the controls, but also for our equipment and possibly the structure… probably our home. The second of course has to do with the performance of our antenna system and it's ability to radiate an efficient signal. Let's treat these separately for now and they will combine into a total plan at the end.

Surge (or Safety) grounding

We need to protect our installation and ourselves from lightning, but… There is no protection against a direct lightning hit! It has way more power than we can shunt to ground safely or our budget can handle.  That is what insurance is for.  We CAN however make our installation an unattractive target to lightning.  We can also take care of any secondary surges and static build up that can destroy equipment and give healthy zaps enough to more than get your attention.  There is nothing more frustrating than trying to talk on a radio and you keep getting zapped on the chin while doing so!  I speak of personal experience here.  Let's let it go at that.  The Safety ground has to consist of enough ground contact surface area to safely dissipate the surges into the soil safely.  Multiple ground rods connected with solid ground wire is best.  You should have one rod where your antenna support structure is whether it be a tower or mast or roof tripod, etc.  It must have at least 4 gauge bare or insulated, NOT stranded wire.  These surges can easily be hundreds of amps.  DO NOT scrimp on the wire.  This is your life you are dealing with.  If stranded wire is used it should be no more than 8 conductors.  Heavy bolt type connectors should be used for all connections.  You should also employ a non corrosive type coating.  All of these connectors and grease are available at your good home supplies or electrical supply houses.  All grounds for the installation should be bonded together at the ground.  NEVER daisy chain grounds.  ALL connections from devices should go DIRECTLY to closest ground point.  Use eight foot copper ground rods for all.  Bond the rods with single or solid bare copper wire.  Drive a ground rod for electrical supply to house if you do not already have one.  Bond it to others with aforementioned wire.  If you have overhead service to house, run wire direct to neutral wire at feed point and use split bolt connections with grease for corrosion.  If you have underground service, ground at meter box.  If your power company objects, run it to your service panel.  You need a minimum of one eight foot ground rod for every protected structure, ie, every mast, tripod, vertical antenna, etc.  These must all be connected together AT THE GROUND.  Run bare copper between the separate ground rods to form a ground system.  The bare copper provides additional surface contact area for the ground system.  It should be underground, but does not need to be deep for any engineering reasons.  Make sure you make yourself a map of the runs for future projects to avoid hitting and digging up the system in the future.  Use heavy duty bolted connectors designed for this service.  If you have access to a ground megger or ground tester the system should be less than 15 ohms.  In sandy soil this can take several rods to achieve.  I have had to put down 3, 32 foot rods (consisting of four 8 foot rods with couplers and driven in with a power driver) in sand to get the measurement needed.  This should take care of our safety grounds.

RF Grounding

RF grounding is considerably different than surge grounding.  First thing is you are working with RF.  Since it is an AC signal it has impedance.  The length of the ground runs has much more to do with the fraction of a wavelength at the frequency involved than the DC resistance of the wire.  While the DC resistance of a ground wire may be only a fraction of an ohm, the impedance (or the AC resistance at RF frequency) can easily be hundreds or thousands of ohms on the same wire.  This can make it pretty difficult to get an effective RF ground.  Remember an RF ground wire is just a short antenna!  We want to make it as  LOUSY an antenna as possible!  We really don't need it radiating extra RF inside our shack.  It is supposed to remove this stuff not cause it.  An effective RF ground needs to be less than a quarter wave length at the highest frequency used.  As you can see there is no such thing as an effective ground for VHF or UHF.  We will concentrate our efforts to 10 meters and above.  This means our ground wire from radio to ground must be about 9 feet or less!  This is still pretty difficult.  All radios, tuners, meters, etc in radio system should be grounded in a star ground configuration.  The common point should be at the tuner if one is used, otherwise a ground bus bar can be purchased at an electrical house.  All Connections to radios should be with either insulated or bare wire with as few strands as possible.  RF likes smooth surfaces best.  DO NOT USE braid for RF connections.  This is an old wives tale!  Your ground run should go directly to the ground where you should have a ground rod for the connection point,  (which will be connected to all your other ground rods in the system as discussed above).  This run must be less than nine feet to be effective.  If you are on the second floor this will make this length impossible.  Use of a shielded ground* wire can stop radiation of the ground wire but you will still have a lousy ground.  Nothing can change this.  Ground wire tuners only turn your ground wire into a counterpoise for your antenna, meaning it WILL radiate.  This will only ensure that the low voltage point of your antenna will be at your radio.  Next we need to form our  RF counterpoise outside at our ground system.  You will next need to add some bare copper wire at the RF feedpoint where your shack ground wire connects to.  I prefer to use bare 8 gauge copper ground wire here.  It is single conductor, bare copper and easily bent and run around house.  Single strand is best but it should definitely be bare even if you have to strip insulation off wire.  Run it around the house or anywhere it will stay out of the way of lawn equipment but not buried deeper than ½ inches.  This is CRITICAL.  RF will not penetrate soil deeper than this at these frequencies.   Those bonding wires you have between ground rods and ground rods do not exist to the RF!   Burying this wire under wood chips or similar non conductive landscaping, etc is the way to go.  This counterpoise should be as long as the wire antennas you have in the air.  For most hams this will be about 130 feet.  Longer is better.  I run all the way around my house.  I have found the eight gauge will push into the spacing used between driveway and foundation when persuaded with the proper tool, (READ HAMMER).  You can connect the loop back on itself at the feed point.  This can add several S units to the receive signal and dramatically reduce noise on the signal, though nothing will help all the noise on 80 or 160 meters.   Years ago I installed a long wire antenna that was about 250 feet long and about 50 feet in the air.  This should work fantastic you say.  I had three ground rods outside window of shack with single solid copper ground wire direct to tuner. Ground wire length was only six feet.   All three rods were spaced about eight feet apart with connecting bare wire interconnecting them… in other words, a really good surge ground.  What I did not realize at that time was how lousy my RF ground was.  We could not tune the antenna on most frequencies and we kept getting zapped from the radio or microphone when we transmitted.  Also, our signal reports were lousy.  So, after consulting some experts, I added 250 feet of counterpoise around the building consisting of some bare 6 gauge copper wire I had.  The radio was on while I rolled it out and a friend was listening to the broadcast on 40 meters, (OK it was night time-best time to do antenna work right!)  Anyway he reported the broadcast was only about S 4-5 on meter.  As I rolled out the counterpoise it rose to 40 over S9 and came in much clearer.  We were able to tune everything easily now and SWR was rock stable.  When we did a signal test, the station we had talked to before accused us of running a contest amplifier.  We could not convince them it was only 100 watts, same as before and the same antenna! 

SUMMARY

Don't underestimate the importance of a good ground system.

Include it into the planning of that ultimate shack you are working on.  Don't scrimp on good copper wire and connectors.  Aluminum can be used above ground but never in ground.  Add one size to aluminum to achieve same current capability.   Ground everything to the system.  A ground run to ductwork in house can alleviate a lot of noise.  A run to water pipes should go direct to ground… NEVER to radios,  NEVER connect radios to ANYTHING inside the house for ground purposes.  Always run all grounds from everything to ground directly.  In other words, your furnace ducts will get one run, your water pipes will get one, etc.  Don't daisy chain to save wire.  If you have a chain link fence in back yard, run a bonding wire underground from ground system to it and bond well.  A solid aluminum or copper wire run along bottom of fence as a bonding device will make it a great addition to the system.  Weave it through the bottom fence fabric and bond every few feet with a split bolt connector.  The power company does this with all their fences around their power stations.  

A shielded ground can be made using RG 8 or similar coax to replace the ground wire.  Connect both inner and outer shields to the Ground rod and connect the center only to the radio.  Add a .1uf 1000 volt cap between ground and shield at this end.

Coax should be grounded at two sites, first at the antenna and then just before entering the house. Is there an advantage in grounding at more than these sites?

With grounds the most common experience is “the more the merrier”. As you add more, however, you usually reach a diminishing returns (no pun intended) situation where there is no *observable* improvement: that’s usually a good place to stop. There are also exceptional circumstances where grounding increases noise problems, but these, in my experience, are much rarer than the pundits who preach against “ground loops” seem to think.

Even a semi-quantitative theoretical treatment of grounding in oversimplified situations requires heavy math at RF. Experimentation is thus required even if one has done elaborate calculations. It’s often easier to use the theory as a guide to what to try, and then experiment.

I would also assume that the antenna is grounded when it is connected to the receiver as the outer braid of the coax is in continuity with the receiver chassis.

What’s ground? If connect the shield of my coax (which is grounded outside) to the antenna input of my R8, I hear lots of junk, indicating that there is an RF voltage difference between the coax shield and the R8 chassis. Last night this measured about S5.5, which is about -93 dBm (preamp off, 6KHz bandwidth). That’s a lot of noise: it was 18 dB above my antenna’s “noise floor”, and 26 dB above the receiver’s noise floor.

This sort of disagreement about ground potential is characteristic of electrically noisy environments. The receiver will, of course, respond to any voltage input that differs from its chassis ground. The antenna, on the other hand, is in a very different environment, and will have its own idea of what ground potential is. If you want to avoid noise pickup, you need to deliver a signal, referenced at the antenna to whatever its ground potential is, in such a way that when it arrives at the receiver, the reference potential is now the receiver’s chassis potential.

Coaxial cable represents one way to do this. Coax has two key properties:

1. The voltage between the inner conductor and the shield depends only on the state of the electromagnetic field within the shield.
2. The shield prevents the external electromagnetic field from influencing the internal electromagnetic field (but watch out at the ends of the cable!).

So, it’s easy, right? Run coax from the antenna to the receiver. Ground at the antenna end will be whatever the antenna thinks it is, while ground at the receiver end will be whatever the receiver thinks it is. The antenna will produce the appropriate voltage difference at the input side, and the receiver will see that voltage difference uncontaminated by external fields, according to the properties given above.

Unfortunately, it doesn’t quite work that way. It’s all true as far as it goes, but it neglects the fact that the coax can also guide noise from your house to your antenna, where it can couple back into the cable and into your receiver. To see how this works, let me first describe how this noise gets around.

The noise I’m talking about here is more properly called “broadband electromagnetic interference” (EMI). It’s made by computers, lamp dimmers, televisions, motors and other modern gadgets. I have all these things. In many cases, I can’t get them turned off, because it would provoke inter-familial rebellion. However, even when I turn them off, the noise in the house doesn’t go down very much, because my neighbors all have them too. In any case, one of the worst offenders is my computer, which is such a handy radio companion I’m not about to turn *it* off.

Some of this noise is radiated, but the more troublesome component of this is conducted noise that follows utility wires. Any sort of cable supports a “common mode” of electromagnetic energy transport in which all of the conductors in the cable are at the some potential, but that potential differs from the potential of other nearby conductors (“ground”). The noise sources of concern generate common mode waves on power, telephone, and CATV cables which then distribute these waves around your neighborhood. They also generate “differential” mode waves, but simple filters can block these so they aren’t normally a problem.

So, let’s say you have a longwire antenna attached to a coaxial cable through an MLB (Magnetic Longwire Balun). Suppose your next door neighbor turns on a dimmer switch. The resulting RF interference travels out his power lines, in through yours, through your receiver’s power cord to its chassis, and out your coaxial cable to your MLB. Now on coax, a common mode wave is associated with a current on the shield only, while the mode we want the signal to be in, the “differential” mode, has equal but opposite currents flowing on shield and inner conductor. The MLB works by coupling energy from a current flowing between the antenna wire and the coax shield into the differential mode. But wait a second: the current from the antenna flows on the coax shield just like the common mode current does. Does this mean that the antenna mode is contaminated with the noise from your neighbor’s dimmer?

The answer is a resounding (and unpleasant) yes! The way wire receiving antennas work is by first moving energy from free space into a common mode moving along the antenna wire, and then picking some of that off and coupling it into a mode on the feedline. In this case, the common mode current moving along the antenna wire flows into the common mode of the coax, and vice versa. The coax is not just feedline: it’s an intimate part of the antenna! Furthermore, as we’ve seen, it’s connected back through your electrical wiring to your neighbor’s dimmer switch. You have a circuitous but electrically direct connection to this infernal noise source. No wonder it’s such a nuisance!

The solution is to somehow isolate the antenna from the common mode currents on the feedline. One common way to do this is with a balanced “dipole” antenna. Instead of connecting the feedline to the wire at the end, connect it to the middle. Now the antenna current can flow from one side of the antenna to the other, without having to involve the coax shield. Unfortunately, removing the necessity of having the coax be part of the antenna doesn’t automatically isolate it: a coax-fed dipole is often only slightly quieter than an end-fed longwire. A “balun”, a device which blocks common mode currents from the feedline, is often employed. This can improve the situation considerably. Note that this is not the same device as the miscalled “Magnetic Longwire Balun”.

Another way is to ground the coaxial shield, “short circuiting” the common mode. Antenna currents flow into such a ground freely, in principle not interacting with noise currents. The best ground for such a purpose will be a earth ground near the antenna and far from utility lines.

Still another way is to block common mode waves by burying the cable. Soil is a very effective absorber of RF energy at close range.

Unfortunately, none of these methods is generally adequate by itself in the toughest cases. Baluns are not perfectly effective at blocking common mode currents. Even the best balun can be partially defeated if there’s any other unsymmetrical coupling between the antenna and feedline. Such coupling can occur if the feedline doesn’t come away from the antenna at a right angle. Grounds are not perfect either. Cable burial generally lets some energy leak through. A combination of methods is usually required, both encouraging the common mode currents to take harmless paths (grounding) and blocking them from the harmful paths (baluns and/or burial).

The required isolation to reach the true reception potential of the site can be large. According to the measurements I quoted above, for my site the antenna noise floor is 18 dB below the conducted noise level at 10 MHz. 18 dB of isolation would thus make the levels equal, but we want to do better than that: we want the pickup of common mode EMI to be insignificant, at least 5 dB down from the antenna’s floor. In my location the situation gets worse at higher frequencies as the natural noise level drops and therefore I become more sensitive: even 30 dB of isolation isn’t enough to completely silence the common mode noise (but 36 dB *is* enough, except at my computer’s CPU clock frequency of 25 MHz).

Getting rid of the conducted noise can make a huge difference in the number and kinds of stations you can pick up: the 18 dB difference between the conducted and natural noise levels in the case above corresponds to the power difference between a 300 kW major world broadcaster and a modest 5 kW regional station.

The method I use is to ground the cable shield at two ground stakes and bury the cable in between. The scheme of alternating blocking methods with grounds will generally be the most effective. The ground stake near the house provides a place for the common mode noise current to go, far from the antenna where it cannot couple significantly. The ground stake at the base of my inverted-L antenna provides a place for the antenna current to flow, at a true ground potential relative to the antenna potential. The buried coax between these two points blocks noise currents.

There has been some discussion of grounding problems on this and related echoes. I believe it has been mentioned that electrical codes require that all grounds be tied together with heavy gauge wire.

I’m no expert on electrical codes, and codes differ in different countries. However, I believe that any such requirement must refer only to grounds used for safety in an electric power distribution system: I do not believe this applies to RF grounds.

Remember that proper grounding practice for electrical wiring has very little to do with RF grounding. The purpose of an electrical ground is to be at a safe potential (a few volts) relative to non-electrical grounded objects like plumbing. At an operating frequency of 50/60 Hz, it needs to have a low enough impedance (a fraction of an ohm) that in case of a short circuit a fuse or breaker will blow immediately.

At RF such low impedances are essentially impossible: even a few centimeters of thick wire is likely to exhibit an inductive impedance in the ohm range at 10 MHz (depends sensitively on the locations and connections of nearby conductors). Actual ground connections to real soil may exhibit resistive impedances in the tens of ohms. Despite this, a quiet RF ground needs to be within a fraction of a microvolt of the potential of the surrounding soil. This is difficult, and that’s why a single ground is often not enough.

A little experimentation with my radio showed that the chassis was directly connected to the third (grounding) prong of the wall plug. I am concerned that by connecting my receiver to an outside ground I am creating a ground loop that involves my house wiring. Can you comment on this?

Yes, you have a “ground loop”. It’s harmless. In case of a nearby lightning strike it may actually save your receiver. My R8 isn’t grounded like that, so I had to take steps to prevent the coax ground potential from getting wildly out of kilter with the line potential and arcing through the power supply. I’m using a surge suppressor designed to protect video equipment: it has both AC outlets and feed-throughs with varistor or gas tube clamps to keep the various relative voltages in check. Of course the best lightning protection is to disconnect the receiver, but I’m a bit absent minded so I need a backup.

This may seem like a trivial point but I recently discovered that the main ground from the electrical service panel in my house was attached to a water pipe which had been painted over. I stripped the paint from the pipe and re-attached the grounding clamp and I noticed a reduction in noise from my receiver.

Not trivial. Not only did you improve reception, but your wiring is safer for having a good ground.

I suspect part of the reason I see so much noise from neighbors’ appliances on my electric lines may be that my house’s main ground wire is quite long. The electrical service comes in at the south corner of the house (which is where the breaker box is), while the water (to which the ground wire is clamped) enters at the east corner. All perfectly up to code and okay at 60 Hz, but lousy at RF: if it was shorter, presumably more of the noise current would want to go that way, and stay away from my receiver.

I am also a little confused by what constitutes an adequate ground. I have read that a conducting stake driven into the ground will divert lightning and provides for electrical safety but that RF grounding systems have to be a lot more complex with multiple radials with lengths related to the frequencies of interest. Is this true?

Depends on what you’re doing. If you’re trying to get maximum signal transfer with a short loaded (resonant) vertical antenna with a radiation resistance of, say, 10 ohms, 20 ohms of ground resistance is going to be a big deal. If you’re transmitting 50 kW, your ground resistance had better be *really* tiny or things are going to smoke, melt or arc.

On the other hand, a ground with a resistance of 20 ohms is going to be fairly effective at grounding a cable with a common mode characteristic impedance of a few hundred ohms (the characteristic impedance printed on the cable is for the differential mode; the common mode characteristic impedance depends somewhat on the distance of the cable from other conductors, but is usually in the range of hundreds of ohms). Of course, if it was lower a single ground might do the whole job (but watch out for mutual inductance coupling separate conductors as they approach your single ground).

In addition, a ground with a resistance of 20 ohms is fine for an unbalanced antenna fed with a high impedance transformer to suppress resonance. Such a non-resonant antenna isn’t particularly efficient, but high efficiency is not required for good reception at HF and below (not true for VHF and especially microwave frequencies).

Much antenna lore comes from folks with transmitters who, armed with the “reciprocity” principle, assume that reception is the same problem. The reciprocity principle says that an antenna’s transmission and reception properties are closely related: it’s good physics, but it ignores the fact that the virtues required of a transmitting and receiving antenna are somewhat different. Inefficiency in a transmitting antenna has a direct, proportional effect on the received signal to noise ratio. On the other hand, moderate inefficiency in an HF receiving antenna usually has a negligible effect on the final result. A few pico-watts of excess noise on a transmitting antenna has no effect on its function, but is a big deal if you’re receiving (of course, one might not want to have transmitter power going out via unintended paths like utility lines: this is indeed the “reciprocal” of the conducted noise problem, and has similar solutions).

Why Wire Diameter Is Important

Here Size Does Matter 

A metal consists of a lattice of atoms, each with a shell of electrons. The outer electrons are free to dissociate from their parent atoms and travel through the lattice, creating a 'sea' of electrons, making the metal a conductor. When an electrical potential difference (a voltage) is applied across the metal, the electrons drift from one end of the conductor to the other under the influence of the electric field.

The larger the cross-sectional area of the conductor, the more electrons are available to carry the current, so the lower the resistance. The longer the conductor, the more scattering events occur in each electron's path through the material, so the higher the resistance. Different materials also affect the resistance.

Simply stated… as electrons move across a wire, they constantly collide with atoms making up a wire. These collisions impede the flow of electrons and are what cause the wire to have resistance. Thus, if the diameter of the wire were larger, it would only make sense that the electrons don't collide as much, therefore creating less resistance due to a larger wire. This is all in accordance to Ohm's law.

The resistance is the ratio of the voltage difference across an object to the current that passes through the object due to the existence of the voltage difference (Resistance = Voltage /  Current). If the object is made of a material that obeys Ohm's Law, then this ratio is constant no matter what the voltage difference is. 

Consider a copper wire that passes some amount of current, say 1 Ampere (A), when a voltage difference of 1 Volt (V) is applied between the ends of the wire. Now consider an identical but separate wire connected across that same 1V source. You would expect that it would also conduct 1A  (R=V/A   R=1/1   therefore R = 1 Ohm).

Now think of joining those two wires together side by side into one, thicker wire. Much like using a thicker pipe to increase the supply of water, it is reasonable to expect that this wire should carry 2 A of current if the potential difference across the wires is still 1 V. Thus, the new, thicker wire will have a reduced resistance of ½ Ohm compared to the original wire with its resistance of 1 Ohm. (R=V/A   R=1/2   therefore R = .5 Ohm).
Why? Basically, a thicker wire creates additional paths for current to flow through the wire. This reduces resistance which results in less generated heat. This is one of the reasons you should use heavy gauge wires when, for example, running a voltage supply to your 12 volt mobile radio. If you don’t, you could find your expected 12-13 volts DC is actually significantly lower. 

American Wire Gauge 

American wire gauge (AWG), also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire. The cross-sectional area of each gauge is an important factor for determining its current-carrying capacity.

The steel industry does not use AWG and prefers a number of other wire gauges. These include W&M Wire Gauge, US Steel Wire Gauge, and Music Wire Gauge.
Increasing gauge numbers give decreasing wire diameters, which is similar to many other non-metric gauging systems. This gauge system originated in the number of drawing operations used to produce a given gauge of wire. Very fine wire (for example, 30 gauge) required more passes through the drawing dies than did 0 gauge wire. Manufacturers of wire formerly had proprietary wire gauge systems; the development of standardized wire gauges rationalized selection of wire for a particular purpose.
The AWG tables are for a single, solid, round conductor. The AWG of a stranded wire is determined by the total cross-sectional area of the conductor, which determines its current-carrying capacity and electrical resistance. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.

Stranded wires are specified with three numbers, the overall AWG size, the number of strands, and the AWG size of a strand. The number of strands and the AWG of a strand are separated by a slash. For example, a 22 AWG 7/30 stranded wire is a 22 AWG wire made from seven strands of 30 AWG wire.

AWG 18 has a solid diameter of about 1mm. Adding 6 halves the diameter, Subtracting 6 doubles the diameter. Adding 20 divides the diameter by 10, and subtracting 20 multiplies the diameter by 10. The following table lists the minimum recommended wire gauge for the length of supply cable in high power radio systems.

Recommended wire gauge for a given amperage and length

Conductivity of Common Metals

The 15 most common metals are listed at right, in order of their conductivity. But, you may say, gold is always touted as best for contacts! It’s true… while gold is not the best conductor, it does not corrode like some other metals and therefore provides more reliable contact over a longer period of time.  

Another surprise is that lead and tin, two of the most common elements in solder are relatively low on the conductivity list. The reason for using them is the fact that lead and tin are used for solder because not only do they have low melting points, but more importantly they form a “eutectic” alloy which has a considerably lower melting point than either one individually (many metals form eutectics), at the disadvantage of higher resistance.

Because its conductivity is the second highest of any metal and its cost is relatively low, copper sees use in most wire, connectors, printed circuit foils and related electrical parts. The resistance of a 24-gauge copper wire 1,000 feet long at room temperature will be about 26 ohms.
Silver's higher conductivity and cost make it a niche product. It's used as wire and solder in specialty electronics. By comparison, a silver 24-gauge, 1,000-foot-long wire would measure about 24 ohms.

Field Day and Special Events: Why ICS?

The Incident Command System 

ICS or the ‘Incident Command System’ is a management structure for planning significant events, both large and small, be they emergencies or not.  It was developed in California to manage large fire situations, but was quickly adopted by other organizations as an effective method to scale up—or scale down a response to a significant event. It is now used universally by emergency services for planning and responding to significant events. Its modular, meaning it can be scaled up, or down, to suit an event.

Amateur Radio Field Day is a significant event, requiring a multitude of people and resources to proceed efficiently. Most clubs, SARC included have a committee structure for their Field Day planning. ICS was first introduced in 2011 and helped to identify duties and responsibilities. In 2012 we hope to build on that experience and further develop our planning and execution so that the process in documented for future years.

Surrey Emergency Program Amateur Radio (SEPAR) provides ICS level 100 training. While we cannot hope to cover that material in a short article, here is a brief overview of ICS positions as they relate to Field Day.


Incident Commander—The Field Day Chair


Safety Officer Has the absolute final say on safety issues in and around the site. Also ensures the site has adequate security.


Information Officer Public Relations or Public Information Officer (PIO)
Media releases before
Hospitality / Public relations at event
Media releases after the event


Planning Section [Section Chief & Committee]
Situation Unit: Ensures FD rules and class are followed in planning the event.
Resources Unit (recruiting): Help other committees schedule people before FD. May utilize Talk-In (Logistics/Services/Comms) to recruit club members in real-time on Field Day.
Demobilization Unit (takedown planning): Planning who/how to take it all down, and (via Logistics) get it all, and everyone, back to where they belong.
Documentation: Preserve guest book, contest logs with Bonus Unit. May help plan logging process, process/submit logs afterwards.

Logistics Section

Service Branch
Communications Unit (this is where we, as Hams, usually fall within someone else's ICS operation). Provides talk-in and any other non-contest comms operations, whether on radio/cell/Internet, whether on ham, commercial or PS licensed, or FRS radios. Might include scoring the NTS points with/instead of Operations/Bonus Unit. Monitor the repeater, 146.52, and club simplex frequency for queries (and a couple of extra points), provide communications liaison with the Safety Officer, relay information for any supply needs. Also, set up wireless or wired internet access.
Food Unit Can break down into Planning & Shopping, Drinks, Snacks, Cooking, Lunch, Breakfast, Dinner and Dessert. Can leverage the Support Branch to find & move the stuff once a list & budget are prepared.

Support Branch
Supply Unit (truck-type transport; leg-work on purchasing for food and supplies; transporting borrowed equipment for other sections' unfilled requirements, e.g. antenna tuner, and return!)
Facilities Unit (arrangements & interface with the City; renting outhouses and other equipment; arranging borrowing of equipment based other sections' unfilled requirements, e.g. generator.)
General Ground Support General hands/labour details (in other words, everyone!) Antenna and tent raising, lugging.
Power Group runs the generators, charges batteries, manages available power. Once you're operational, it's the primary component of Support. 

Finance & Admin Section (Typically the organization's Treasurer)

Operations Section 
Deputy Operations Chiefs who lead while the Chief sleeps and take on the role of Station Manager. License trustee; ensures the operators are working the right band with the right equipment and antenna; ensures FD rules and class are followed. Also ensures the operator schedule is followed so everyone has an opportunity to participate.
Operations is divided into functional Branches as needed; with further geographic or functional Divisions or Groups, as needed. Most of our functional Divisions can naturally be called "Stations".

Contesting Branch: Each Station counted in our 3-Alpha Field Day class would be one "Division" or "Group" for ICS purposes, both for planning and operations. 
HF SSB Division Station (Station leader; shift operators, shift loggers)
HF CW Division (ditto)
VHF+ Division(s) (ditto)
Digital Division(s) (ditto)
Satellite Division (ditto)

Bonus Branch: The bonus points may cross into other ICS Divisions, but may be included in Bonus Branch
Handling NTS traffic (for points)
Any other special points available (satellite or digital)
Making Natural Power contacts (for points)
Demo points

It may sound like a lot of positions, but the advantage is that everyone in the structure knows who their team leader is and what their responsibilities are. Obviously there are more positions than people so, in an organization an individual may have more than one responsibility. In the end you should have a structured approach to Field Day with a written manual that others can follow.

For an on-line ICS-100 course, visit the FEMA website: https://emilms.fema.gov/IS100c/curriculum/1.html

Using Fuses Effectively

A Communicator Reprise: May 2012

In today’s electronics, fuses play a very important role that is frequently misunderstood, with the result that expensive equipment is often not fully protected, and this can result in expensive repair bills. The history of fuses is as old as the use of electricity and probably goes back to the time of the first short circuit! At first, fuses were simple open-wire affairs, but around 1890 Edison enclosed the wire into a lamp base to make the first enclosed fuse. By 1904 the Underwriters Laboratories had introduced specifications covering fuse size and ratings to meet the safety standards of the period. In 1927 Littelfuse started making the first of their range of low amperage fuses for the budding electronics industry. Since that time many new types of fuses have appeared on the market, some with very special characteristics for particular types of protection. Today the choice is extremely large and protection can be provided inexpensively and the risk of expensive repair bills reduced.

Purpose of a Fuse

A fuse is a device which is wired into an electrical circuit to prevent excessive current flowing when a fault occurs. On overload the wire forming the fuse element will heat up and melt (‘blow’) thereby breaking the circuit, interrupting current flow, preventing damage from excessive current to the remaining circuits. It is the electrical equivalent of a "safety valve".
The most important characteristic to the user is the current rating which, unfortunately, is often misunderstood. The current rating of a fuse is established by the manufacturer after a series of tests under controlled conditions. This enables the manufacturer to publish a set of specifications for its product which design engineers can use to decide which is the correct type of fuse for a particular circuit. In order to understand the current rating of a given fuse it is important to know the conditions under which this rating was achieved. There are three main groups of fuses:

1. slow-blow (or anti-surge),
2. normal quick acting, and
3. very fast acting

There is also a fourth type known as time delay fuses. 
Each of these types will protect a circuit from excessive continuous current, but act very differently under surge or short time conditions. The fitting of the wrong type could mean no protection at all is being provided, or fuses that keep "blowing" for no apparent reason.
Let’s take a detailed look at each type. The blowing time in seconds plotted against percentage overload for the three main types of fuse mentioned above is shown.


It can be seen that up to 100 per cent overload there is very little difference between the three types. But if we take a current overload of say 500 per cent we can see that the fast acting fuse blows in 0.001 seconds (a millisecond) and the slow-blow in about 2 seconds with the normal acting fuse at about 0.01 seconds. Quite a considerable difference between the three types. In fact the ratios (taking our normal acting fuse as the reference) work out at one tenth of the time for our fast acting fuse and 200 times longer for our slow-blow type! A very big difference indeed and more than enough to ‘release the smoke’ in expensive semiconductors under fault conditions.
Temperature also has an effect on the current rating. As the ambient temperature becomes lower the amount of current required to "blow" a fuse becomes higher and this can make a considerable difference to the blowing times under surge conditions.
Ah, you may be thinking, let's use a fast acting fuse all the time and be safe. Regretfully this is not practical as many circuits have a high surge current when first switching on, or switching to change operating conditions.

Construction

Let us now consider the construction of a typical cartridge fuse. First it has to have a body or barrel and this is normally made of glass or ceramic material. The barrel will have some form of termination at each end, usually brass or copper, which has been plated to prevent corrosion. The fuse element will be connected between the two end terminations and enclosed within the barrel. 
It will consist of a single wire in the case of a quick acting fuse, or may be one or more wires arranged in a specific way for delay and anti-surge types. Sometimes a filler is used to modify the action of the fuse and this may be sand or quartz powder. This filler will absorb the energy of the arc when the current is interrupted.
Fuses are of course marked in some way as to type and ratings, normally on one or both of the end caps and in addition there may be an indication of one of the many standards that the particular fuse complies with, e.g. BS, SEMKO, etc. The size of fuse may vary but there are a number of standard sizes and the most common are the  Standard metric which is 20mm long by 5mm diameter and the US standard of 1 x .25 inch diameter.  Many other sizes are available ranging from 5mm long to over 200mm. 
Particularly in automotive applications there are also ‘blade’ type fuses (see graphic below), and of course there are a number of other styles available for special purposes.

Fuse Characteristics

There are two main characteristics which will concern the Amateur and these are maximum continuous current rating and the surge rating of slow-blow types. The rupturing capacity of a fuse may also be important and for completeness is mentioned here. A high rupturing capacity fuse is capable of interrupting currents in the order of thousands of amperes. It would have a ceramic body and also contain an arc-quenching medium. Non-HRC fuses (more common in Amateur Radio equipment) do not have an arc-quenching medium and are only suitable for surge currents up to about 50 amps. With higher currents than this they would be very likely to explode when they blow.

Fusing Speed

As we have seen, a quick-acting fuse is designed to react both to short and long term overload conditions. They are very robust in construction and will withstand shocks and vibration. But they do tend to have a higher resistance and the voltage drop caused by this may be a problem in some applications. This higher resistance also means that more heat is produced and this must be effectively dissipated.
Time delay fuses will react to long term overload currents but will withstand transient surges without harm; several types are available. For example, one type has what looks like a spring inside the barrel and these will stand up to surges of around ten times the normal rating for 75 milliseconds. Another type has a "blob" in the middle of the fuse element and this type has a reduced surge capacity, typically ten times rated current but only for 25 milliseconds. Time delay types have a very low resistance and can be used in enclosed places as there is little self-generated heat but they are only available in the lower current ratings. Both the "spring" and the "blob" type are time delay fuses.
So far we have mentioned only the current rating of fuses, but they also have a maximum voltage rating. This voltage rating has no effect on the current rating but is important nevertheless. When a fuse "blows" an arc is developed between the two ends of the broken fuse element and, if the voltage across these ends is high enough, the arc will be maintained and the current will not be interrupted. This condition could result in considerable damage to the equipment. Arcs are readily produced in high voltage circuits or where inductive loads are being used and, in these conditions, the voltage rating of a fuse must not be exceeded. Fuses can be used at their current rating at all voltage levels up to their maximum. When it is known for certain that, although the circuit has a high voltage present, the power available is limited, it is possible to use a fuse at a higher voltage than that for which it is rated. This is common practice in domestic electronic equipment and quite safe. But. if in doubt, keep within the voltage ratings given by the manufacturers.

Mobile Fuse Applications

In one sentence: Place the fuse as close to the battery as possible in both the positive and negative line.

That’s good advice because if for any reason the positive wire’s insulation is damaged and the wire touches the chassis or engine (a hot manifold is a frequent cause of this problem) then it will blow the fuse if it is close to the battery but not if it is between the radio and the short.

It’s also good practice to place a fuse in the negative line.  Many hams think that is unnecessary because you will not cause a short if the negative wire touches the metal of the vehicle.  So why place a fuse in this line? In many installations the negative wire goes straight back to the negative terminal of the battery.  If the battery cable develops resistance between the cable and the body of the vehicle by rust or corrosion or the wire itself corrodes to the point that it is not a good conductor this type of installation can cause problems. When the engine is being started a lot of current is being drawn from the battery and the wiring to the mobile radio is not designed to handle any where that much current.  Simple Ohm’s law will tell you that the maximum current will flow through the path of least resistance and if that path happens to be through the negative wire of the radio to the negative terminal of the battery then that is the where the most current will flow. Frequently the unit is not grounded well at the mounting bracket but the shield side of the coax makes a good ground by the antenna mount.  In that case the current for the starter will attempt to flow through the coax shield to the coax connector on the radio then on to the negative wire to the battery. If that wire is not fused the coax shield will smoke. If the radio is grounded at the mount, the negative wire to the battery is not big enough to handle the load and it will smoke.  Either way there is a fire danger.

This type of hookup is not recommended.  If you do this and the fuse blows you may not know it is blown because the radio finds sufficient contact between the mounting bracket and/or the antenna ground to continue to operate.  The resistance between the battery and the vehicle chassis does not have to be high enough that the vehicle will not start to cause this phenomenon. The antenna ground and the mounting bracket are not designed to be the negative source for the DC power of the radio and it will cause more problems than you can imagine. Tracing the source of these problems can drive you crazy. The suggestion is therefore to run the ground wire to the chassis of the vehicle. Use an eye terminal with one outer locking lock washer between the head of the screw and the lug and another between the lug and the chassis.  Scrape the paint off the place where the lug will come in contact with the metal. Run the screw down tight but do not strip it out.

A Short Course On Baluns

A Communicator Reprise: April 2012

Before getting into this, it is necessary to describe a somewhat puzzling phenomenon (called "skin effect") associated with radio frequency currents.

SKIN EFFECT

High frequency AC currents in a conductor flow only in that portion of the conductor which is very close to the surface.  Very close being 0.1 mm (the "skin depth") or less.  While a wire has only one surface, the shield on a coax cable, being a cylinder, has two surfaces - an inner surface and an outer surface.  Consequently, you can have a high frequency AC current flowing on the inner surface and an entirely different one flowing on the outer surface, with neither of them affecting each other. It's like there's an insulator keeping them separated.
Weird but true.

BALUNS

Unless precautions are taken to minimize it, all coax fed antennas will have significant current flowing on the outside of the coax shield while transmitting.
If the antenna is a horizontal dipole with the coax hanging straight down then the coax acts as a vertical antenna.  This is because this  current flowing on the outside of the shield will radiate energy exactly as a vertical antenna would.  
For casual ham HF operation, this can be a good thing as radiation will take place over a wider range of elevation angles which in turn makes it possible to make contacts over a larger range of distances.  However, for a communications antenna system designed to have a specific radiation pattern, this unwanted radiation from the coax changes the pattern and reduces the effectiveness of the system.
When receiving, the coax still acts as a vertical antenna and couples whatever it picks up into the actual antenna and from there into the receiver.
An example of these effects on a Near Vertical Incidence Skywave (NVIS) antenna system follows:

TRANSMITTING

For NVIS the desired radiation elevation angles (the range in angles with respect to the horizon over which the antenna radiates most of the transmitted energy) is about 60 to 90 degrees, 90 degrees being straight up.  A horizontal dipole 1/4 wavelength or less above ground will provide this.

If this antenna is fed with coax and no precautions are taken to minimize current flowing on the outside of the shield, the shield will act as a vertical antenna with a range of radiation elevation angles between about 5 to 40 degrees.  The amount of power radiated at these low angles can be 50% of the power radiated at the desired elevation angles.  This means that less power is available to be transmitted at the desired high angles.  In addition, this power radiated at low angles can cause interference to other stations thousands of miles away.

RECEIVING

This is where the coax shield acting as an antenna really sucks.
The shield, acting as a vertical antenna, will pick up those previously mentioned stations several thousand miles away and feed them into the dipole which will then happily send those signals to the receiver where they will interfere with the signals you want to hear.  
In addition, most noise on the lower HF bands is caused by lightning in the tropics.  If your antenna responds only to high angle signals (NVIS) it won't respond to these lightning induced static crashes because they arrive at low angles.  Consequently, you won't hear them.  However, if the coax shield is acting as an antenna you will hear them and they may make it impossible for you to copy the signals you want to hear.
Because the coax comes right into your station, it runs close to all kinds of noise generating equipment such as computer monitors, plasma TVs, switch mode power supplies, etc.  Because the coax is acting as an antenna, it will pick up all kinds of garbage that the dipole won't hear because it's much further away from these noise sources.

BALUNS TO THE RESCUE

Well, not just any old balun. "Balun" is a contraction of the phrase "balanced to unbalanced". An ideal horizontal dipole is said to be "balanced" with respect to ground.  What this means is that:
The voltage between ground and the point where one wire of the feedline is connected to the antenna is exactly equal (but of opposite polarity) to the voltage between ground and the point where the other wire of the feedline is connected to the antenna.
The current flowing out of one wire of the feedline into the antenna is exactly equal to the current flowing into the other wire of the feedline out of the antenna.

This is an ideal which is never achieved in practice.  Things like one end of the antenna being lower than the other, closer to a tree or building, etc., will all cause the currents in the two legs to be different.  Consequently, no antenna is truly balanced.  Some come close, though.
Feedlines such as the old TV twinlead, window line and ladder ("open wire") line are all considered to be balanced as they are symmetrical with respect to ground (as long as one side of the feedline isn't closer than the other to ground, metallic objects, etc).  
Our transmitter outputs are "unbalanced" with respect to ground.  This is because the outer shell of the output coax connector is connected directly to ground through the metal case of the radio. Similarly, the coax cable we connect to the transmitter is unbalanced as the shield is connected directly to ground via the coax connector on the radio.
So now we have a balanced antenna to which we want to connect an unbalanced coaxial cable. Physically, this is easy to do, we just connect them.  But, as soon as we do, we destroy the balance of the antenna and we get current flowing on the outside of the coax shield with all the resulting bad effects.

So, what we need is a box between the antenna and the coax to make the transition between the balanced antenna and the unbalanced coax feed line, and, yes, these boxes exist and they are called baluns.

There are two types of baluns:

Voltage Baluns

These force the voltage between ground and the point where one wire of the feedline is connected to the antenna to be exactly equal (but of opposite polarity) to the voltage between ground and the point where the other wire of the feedline is connected to the antenna.  The idea here is that, if the voltages are equal, the currents will be too.

However, as most supposedly balanced antennas are at least somewhat unbalanced, the currents in the two legs will not be the same.  This causes a current equal to the difference between them to flow on the outside of the coax shield.  i.e. the coax shield now acts as an antenna.  Just what we DON'T WANT.

Current Baluns (also known as "Current Chokes")

These force the currents in the two legs (halves) of the dipole to be equal.  As there is now no difference in these current values, no current flows on the outside of the coax shield.  This is just what we want, so these are the ones to use.

SUMMARY

Every coax fed antenna system designed to have specific characteristics needs a current balun located at the transition between balanced and unbalanced.  These are often built into VHF and UHF antennas (skirts, sleeves, etc.) but are generally separate items in HF systems.

Without a current balun the antenna is strongly coupled to the outside of the coax shield. 

This means that energy transmitted by the antenna will be coupled into the coax shield which will reradiate it and thereby affect the radiation pattern of the antenna system.

It also means that signals picked up by the coax shield acting as an antenna will be coupled into the antenna and passed to the receiver.

It is important to note that, like any other conductor, the coax shield will pick up signals and re-radiate them.  The current balun simply ensures that these re-radiated signals don't get coupled into the antenna and so don't reach the receiver.

APPENDIX

SKIN EFFECT DETAILS

If you pass a DC current down a wire, the current flows uniformly down the wire.  i.e. the amount of current flowing down the centre of the wire is the same as the amount of current flowing near the outer edges of the wire.

This is not true for AC currents.  For a current with a frequency of 1 MHz in a copper wire, the current will be concentrated in a region with a depth of less than about 0.1 mm from the perimeter of the wire.  This 0.1 mm is called the "skin depth".  The skin depth gets smaller the higher the frequency.  It doesn't matter if the wire is 1 cm or even 1 metre in diameter, only this 0.1 mm thick "skin" has significant current flowing in it.

See http://en.wikipedia.org/wiki/Skin_depth but skip the eye-glazing math and check out the chart at the end.

As mentioned earlier, the shield of a coax cable isn't a wire with one surface - it is a cylinder with two surfaces, an inner and an outer.  This means that, provided its thickness is more than a few skin depths at the frequency of interest, you can have a current flowing on the inside of the shield and an entirely different current flowing on the outside!  This is because neither current penetrates far enough into the shield material to affect the other current.  It's just as if there were an insulator keeping them separated.

The point to take away from all this is that, counter-intuitive as it may be, you can have two distinct AC currents flowing in a coax shield, one on the inner surface of the shield and one on the outer.

~Jim Smith VE7FO

Using Multi-Meters

A Communicator Reprise: March 2012

Using Multimeters—Part 2

Last month we looked at multi-meter types. Multi-meters have the ability to measure voltage, current and resistance and more expensive models may add other functions such as temperature. A basic addition to your household tool kit, there are low cost multi-meters available, frequently on sale for less than $10. I’d suggest purchasing a digital rather than analog model as a digital meter is easier to use and will suffice for basic measurements.

Digital models are generally "auto-ranging", a useful feature because you don't need to change the dial to measure different levels. If you think you might be using it in low light, consider getting one with a "back-light."
The first rule for getting the most out of your multi-meter is to read the manual. The manual will have instructions for basic operation of the instrument and safety information about potential dangers. Once you have read the manual, added the batteries, and attached the probes (the wires, which are usually red and black), try some of the example measurements below.

Basic Multi-meter Tests

Resistance Test

Set the multi-meter to read "resistance." Check that the two probes are inserted in the right holes.

What does the readout say when the probes are not touching anything? When the two probes are separated, there is an infinite resistance separating them, since air does not conduct electricity. Make a mental note of your multi-meter's readout for infinite resistance, because it varies with the manufacturer.
Touch the two probes together. Now what does the readout say? When you touch the two probes together, the resistance is close to zero. The metal tips are excellent conductors and the wires offer little resistance to current flow.

Try this…  I first did this as a science fair project. Set the knob to the highest Resistance scale on the meter Dampen two fingers and press one probe to each fingertip. Do you get a reading? With dry fingers you probably won’t get a reading. Dry skin has a resistance of about 1 million ohms, whereas the resistance of moist skin is reduced by a factor of ten or more.
Try it with different liquids including salt water. Did the resistance change? What you are seeing is a Polygraph (lie detector) in its simplest form. As the subject is stressed from telling an untruth, the body produces perspiration which changes the skin’s resistance [scientifically known as Galvanic Skin Response]. Also measured in a professional instrument are blood pressure, pulse and respiration. Once calibrated, a polygraph and trained operator can record and interpret the readings to determine when the subject is truthful or not. For more experimentation check Google or have a look here for a basic kit.

Measure the resistance of some resistors that are not attached to a circuit. For example, test resistors of 100 Ω (ohms), 10,000 Ω, and 1 MΩ (mega-ohm, or 1 million ohms). You can buy these online or at a local supplier. Touch the probes to the wires on either side of the central cylinder. Watch the units: a "k" means kilo-ohms (thousands of ohms), and an "M" means mega-ohms. 
Never measure resistance in a circuit when power is applied. You must also discharge capacitors in a circuit before measuring resistance, because if there is any source of current other than the multi-meter itself, you will get erroneous readings.

Voltage Test

Touch the probes to the terminal ends of a 9-Volt battery [see photo]. You should get a reading of approximately 9 Volts. This one reads 7.57 volts so is obviously spent. The battery has a positive [red] and a negative [black] pole. Note that your multi-meter also has a positive and a negative probe. If you attach the positive probe to the negative side of the battery, it will still read voltage, but it will have a negative sign in front of it.

Current Test

This is probably the trickiest reading to make and one that can damage the meter should you pass too much current through it. Set the multimeter to read "direct current (DC)." Important: Check your multimeter to see where the probe should be plugged in so it reads "current."

Don’t be shy to experiment with your multi-meter.
You will likely find a multitude of uses for it around the house.

In order to measure current, you have to open up the circuit and attach the leads from the multimeter so that the current flows through the multimeter in series. To do this, use jumper wires and wires with alligator clips to add the multimeter to the circuit, as shown.
The current now flows from the 12 volt source through the switch, resistor and the multi-meter because it is part of the circuit.  Because it is connected in series, the meter can be inserted at any point in the circuit shown and show the same reading.