Ham To Ham #36 - September 1998

You're Input is Always Welcomed!

73's Ham To Ham column c/o Dave Miller, NZ9E 7462 Lawler Avenue Niles, IL 60714-3108 USA E-mail: dmiller14@juno.com

Moderator's note: Roger and Ron Block of PolyPhaser Corporation have put together a well written series of tips and suggestions on how we can effectively protect our ham radio stations from the effects of a lightning strike. The series began in the January 1998 Ham To Ham Column and Part 8 of that series appeared last month. Part 9 follows:

Lightning protection - what your mother never told you! - Part 9

Longevity After a ground system has been installed, inevitably it begins to age. Copper and other metals are attacked by acids while aluminum is attacked by bases. In addition, other chemicals may be present in the soil which can cause decreased effectiveness of the grounding materials.

Maintenance testing is important. While some ground systems will last 30 years, others are not nearly as durable. The proper way to test the effectiveness of a grounding system is to use an earth resistance meter, which will provide a "fall of potential" type test.

Safety hint ... Use caution when connecting a ground system to the existing electrial utility ground rod. Depending on ground conductivity, harmonic and other currents could flow causing a spark when connected.

Other Helpful Hints Having VSWR trouble or telephone interference with your multi-band HF vertical? When you have a ground mounted multi-band HF vertical antenna, the ground radials normally connect to the coax cable's shield. Since the equipment end of the coax line will be at some random length (which can approach a 1/4-wave or some multiple thereof) from the antenna, RF energy, thinking that the coax's shield is a radial, will show up as high VSWR on that band or bands. It can be corrected by decoupling the coax with a "poor man's balun". Even though a ground mounted 1/4-wave vertical is not a balanced antenna (and shouldn't need a balun), the technique works because the coil also acts as an RF choke to RF currents traveling on the cable's outside shield. RF currents on the inner surface of the shield are a necessary part of the circuit path, but not on the outside surface. You can easily form an RF choke by making an 8 turn coil, 6 inches in diameter right in your coax feedline. Give it a try if you're experiencing the problem mentioned.

If your coax goes up from ground level to a first or second story level, the radiated near-field energy from the antenna will also give "higher VSWR like" indications. This can be fixed by adding another coax coil (in the same manner as above), but this time near the transmitter. This "choke" will provide a high impedance to the captured RF on the coax's outside shield surface and reflect it back. If a decoupling coil is present near the antenna feed (described above), the RF will continue to bounce back and forth until it's either radiated or lost due to resistance, with no effect on your measured VSWR. Additionally, if you don't eliminate the RF riding on the outside of the coax cable, it can make the equipment cabinet high (hot) with RF voltage. Since the cabinet is connected to the power safety ground, and if you're not using the recommended single point grounding technique, the safety ground will carry the RF to the telephone company installed protector. Chances are, the utility safety power ground is poor or is highly inductive. The RF will then likely fire the telephone company's protector, causing interference to your phone. It can even cross-couple to other lines in the same cable run to the central office.

Providing a good earth ground for both lightning and RF, interconnecting the utility safety ground into your overall ground system, using a single-point ground configuration (as we've discussed in pervious installments) and installing a low inductance interconnect path between the single-point and the external ground system, will do a lot toward eliminating these RFI problems (in addition to protecting you from lightning surge currents)."

Moderators note: In another section of this series we were warned about coils in the coax cable feedlines acting as air-wound pick-up coils for the magnetic field generated by a lightning stroke. That danger still exists (as previously detailed), so the suggestions given here are not completely without their inherent drawbacks. One solution may be to enclose the coils of coax just mentioned inside of a magnetically shielded metal container that's properly bonded to the single point ground (at the outdoor end) and to the single-point ground (at the station end).

"Do you know why steel ground rods are copper plated? If you answered 'to increase conductivity' you'd better read on. The base metal, steel, is more conductive than the best soil or even salt water. The real reason is for corrosion resistance. Copper, silver, mercury and gold all have high resistance to corrosion. Those metals that are never found free in nature, like aluminum and magnesium, are easily corroded. Noble metals (like copper) become the cathode when joined together with less noble metals in the presence of an electrolyte (ionic water). Less noble metals become the sacrificial anode and corrode away.

Graphite (though not technically a metal) is even more noble than silver and certainly much nobler than copper. Therefore, if a graphite backfill material is used as a ground enhancer to surround copper, the copper will be sacrificial to the graphite and will dissolve away into the ground.

The following effect the amount and speed of corrosion both above and below the soil:

1) Water: The presence of water, mixed with contaminants, is the basis of galvanic corrosion. Pure rain water is slightly acidic (pH 5.5 to 6.0). It picks up carbon dioxide as it falls, which creates carbonic acid. It can start attacking some metals, even copper, without being in a junction. The ions etched from the copper go into solution in the rain water. As this rain water drips on galvanized tower sections, it will cause the zinc to combine and wash off. This leaves the bare steel to oxidize away.

2) Oxygen: This is the main corrosion accelerator. Rain water also picks up oxygen as it falls through the atmosphere... water is an excellent carrier of oxygen.

3) Temperature: Generally the higher the temperature the faster the chemical reaction.

4) Texture of the metal(s): Glass smooth surfaces are less likely to corrode than rough finishes.

5) Hydrogen Sulfide: A gaseous product of exhaust emissions, it combines with rain water creating acid rain.

6) Chlorine: Tap water can have an acidic effect on underground materials.

7) Inert gases: Helium displaces oxygen and reduces the corrosive effect.

8) Alkaline: Although some alkalis tend to incrrease the rate of carbon dioxide absorption from the air (which creates corrosive carbonate solutions), slight amounts of alkalinity can reduce corrosion rates.

9) Salts: Sodium chloride (found just about everywhere) increases the soil conductivity and also increases the corrosion process (in nearly the same proportion to its concentration). Other naturally occurring salts or man added salts will do about the same. Only sodium carbonate or phosphate and potassium ferricyanide form a protective film that prevents further corrosion.

10) Micro-organisims: Both bacteria and fungus can deteriorate metal. Some will give off acids in trapped water, or, when they die, will decompose into acids.

Types of Corrosion There are several types of corrosion. Listed below are the common names given for descriptive purposes:

1) Uniform Etch: A direct chemical attack from salts, urine and acids. If allowed to continue, a polished surface will dull and then take on a rough or frosted appearance.

2) Pitting: Tiny pin holes from localized chemical or galvanic attack.

3) Intergranular: Usually galvanic, this is a selective attack along the grain boundaries of an alloy metal. We have referenced this as "de-alloying." Typical corrosion-resistant alloys can break down when corrosion actually works on the individual components of the alloy.

4) Exfoliation: Found on extruded metals, the corrosion occurs just below the metal surface and causes a blister to form. This appears where the extruding dyes have forced the crystal structure of the metal to change direction.

5) Galvanic: This is the classic two-dissimilar-metal-connection, with a water electrolyte bridge, and is the most basic of corrosion problems.

6) Concentration Cell: As the amount of oxygen reaching the electrolyte varies, the rate of corrosion will vary accordingly. High concentrated areas of oxygen will have high levels of corrosion.

7) Stress: More corrosion will occur where high tensile stress is applied. This occurs where metal is bent or where rivets have been driven in. Metals that have been cold worked (bent back and forth several times). Copper is easily cold worked and should be annealed (stress relieved by heating). Stress corrosion appears as a crack running parallel to the metal's grain.

8) Fatigue: Another form of stress corrosion where pits are defined along the grain. Additional stress begins to concentrate around them and cracking occurs at the bottom of the pits.

9) Filiform: Thread-like filament corrosion occurring under painted surfaces where water and oxygen have penetrated and form a corrosion concentration cell."

That's Roger's and Ron's presentation for this month. If you'd like to see the original, unabridged version of this series, you can contact PolyPhaser Corporation, Customer Service Department, 2225 Park Place, P.O. Box 9000, Minden, NV 89423-9000 and ask for their Special Bulletin, "Protection to Keep You Communicating" (copyright 1995). You can also pay a visit to PolyPhaser's home pages on the world wide web at: http://www.polyphaser.com/. PolyPhaser's web site also supports text downloads of the original material that's going to be condensed here, plus other related texts on the subject. The PolyPhaser Tech Line telephone BBS at (702)782-6728 is also available to interested readers. The communications parameters are: Data bits - 8, Parity - None, Stop bits - 1, Baud rate - 300 to 14400. If you are dialing in for the first time, the Tech Line requests your name, address and telephone number. You will also need to create a password. Once you've logged-on, just follow the menus to navigate around the Bulletin Board. The Ham To Ham column will continue this series on protecting your ham station from the destructive effects of a lightning strike with Part 10, the final installment, coming up next month.

Making the cut!

Money saving tips are always popular among our ranks, and here's one from Stephen Reynolds N0POU: "Used, non-working camcorders are popping up more and more at garage sales, flea markets and even hamfests these days. Many people simply replace an inoperative camcorder with a newer one, rather than paying the high price of having an older model fixed. Since most camcorders come with a carrying case, battery and battery charger, even if you'd rather not get involved in trying to fix the camcorder itself, these accessories can often be very useful in and of themselves.

The carrying cases are usually pretty well made, so a few minutes modifying the case for other purposes can be well worth the effort. If needed, the inside of the typical camcorder case can usually be cut-away, leaving the outer shell only for storage of ham gear for QRP operation, field day, vacation or other needs. The best method that I've found is to use a sharp utility knife to cut just under the inside lip (as shown in Figure 1). On some cases, you'll also have to cut out some braces or separators, but they do normally all come out. The gutted case can then be lined with foam rubber, and custom separators can be added as needed to accommodate your own particular ham equipment.

Need an auxiliary battery for your hamfest HT or perhaps as a backup to a QRP rig? Some of the older camcorders have fairly husky rechargeable battery packs as a part of their package. It's often possible to remove the camcorder's battery holder (the holder that the battery clips onto) from the body of the camcorder without a great deal of work. Some simply snap onto the body, others are held in place with several small screws, but a few may require some surgery in the form of a sharp utility knife and/or a fine-toothed hacksaw to part them away from their hosts! Be very careful if you encountered the later, it may not be worth the risk of personal injury and/or damage to the holder itself. Providing that the battery and it's charger are good working order (you tried that first of course), you should now have a combination that will serve you for some time in various applications for your ham radio pursuits. Remember, I'm pulling for you, we're all in this together!"

A "Close-in" antenna for 40

Bruce Cameron WA4UZM describes his easily duplicated 40-meter wire dipole in this piece: "While the most basic amateur antenna remains the simple dipole, if you construct it strictly from 300 ohm ribbon lead (as often recommended in the books), it probably won't even come close to matching your modern, 50-ohm-only solid-state transceiver's input/output impedance. For years, I've successfully center-fed a 40-meter dipole, consisting of about 64 feet of wire, with either RG-8 or RG-58 50 ohm cable, and with the flat-top of the antenna only 8 to 10 feet above the ground. The low overall height gives a very high radiation angle, which is ideal for close-in work or state-wide nets. The mismatch is tolerable (being about 40 ohms instead of 50) and the tuning is fairly straight forward.

Careful tuning is a must for best results, but it doesn't take all that much effort or equipment. The easiest way is with one of the newer, self-excited RF bridges, coupled with lots of patience. I've found the best way is to start with 66 feet of wire, looped through egg insulators at each end, doubled back on itself, and temporarily secured with split-bolts. Try to keep both halves of the dipole as close to the same length (symmetrical) as you can, for best results. You should be able to end up with an SWR of 1.5 to 1 or less (though you'll probably notice an SWR change between wet and dry ground). My present antenna is simply made of split zip-cord, I've heard some people say that insulated wire is less prone to noise."

Moderators note: If you're not familiar with the split-bolts that Bruce refers to in his tip, stop by your local hardware store or electrical supply shop and show them the drawing in Figure 2. A split-bolt, as the name implies, is basically a brass bolt, with a slit down the center and a free-sliding clamp and nut on one end. The main antenna wire, and its looped-back-end, occupy the space inside of the slit, and the free-sliding clamp piece and nut are snugged-up to hold the combination firmly in place. If you need a little more or a little less wire during your antenna tune-up trials, just loosen the nut on the split-bolt and adjust the length of wire as needed. A split-bolt on each wire end can also serve as the permanent method of securing the assembly once it has been successfully tuned. Additionally, I think that Bruce's reference to insulated wire being less prone to noise may stem from the fact that when bare stranded copper wire is exposed to the elements, the individual copper strands tend to partially self-insulate from each other as copper corrosion develops over time. As the antenna wire moves, due to the wind or expansion and contraction with temperature changes, small amounts of noise voltage may be generated by the partially insulated individual strands rubbing together. Weather-tight, insulated, stranded conductors and bare solid wire don't exhibit this tendency. Also keep in mind that any insulated antenna wire will add "apparent" length to the dipole's size, so the exact end-result-length may be somewhat different from what the formulas and antenna book tables show as the normal "finished length" of a dipole for a particular frequency. The finished antenna's height-above- ground (and surrounding objects in the near-field) will also effect the antenna's '"naturally" resonant frequency. Finally, plain copper wire (even if covered with plastic insulation) will tend to stretch more than copper-coated steel antenna wire, so some adjustment with time and weather conditions may be necessary (significant sag might occur with a heavy winter icing for instance).

Murphy's Corollary: Everything, except getting into hot water, always takes longer than expected.

That's all for this month, thanks for tuning in the Ham To Ham column and please keep this column in mind when you have something that you'd like to contribute. Some of the best information that we can practically apply to our day-to-day ham radio applications comes from others who've encountered similar situations ... and found workable solutions. As the Ham To Ham column concludes its 3rd. year on the pages of 73 with this issue, many thanks, as always, to our loyal contributors, including:

Roger Block, President PolyPhaser Corporation 2225 Park Place P.O. Box 9000 Minden, NV 89423-9000

Stephen Reynolds N0POU 510 South 130th. Street Omaha, NE 68154

William Bruce Cameron WA4UZM 430 Doric Court Tarpon Springs, FL 34689-2524

If you're missing any past columns, you can probably find them at 73's Ham To Ham column home page (with special thanks to Mark Bohnhoff WB9UOM), on the world wide web, at: http://www.rrsta.com/hth

Note: The ideas and suggestions contributed to this column by its readers have not necessarily been tested by the column's moderator nor by the staff of 73 Magazine, and thus no guarantee of operational success is implied. Always use your own best judgment before modifying any electronic item from the original equipment manufacturer's specifications. No responsibility is implied by the moderator or 73 Magazine for any equipment damage or malfunction resulting from information supplied in this column.

Please send any ideas that you would like to see included in this column to 73 Magazine's Ham To Ham column, c/o Dave Miller NZ9E, 7462 Lawler Avenue, Niles, IL 60714-3108, USA. We will make every attempt to respond to all legitimate ideas in a timely manner, but please send any specific questions, on any particular tip, to the originator of the idea, not to this column's moderator nor to 73 Magazine.