Ham To Ham #35 - August 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 7 of that series appeared last month. Part 8 follows:

Lightning protection - what your mother never told you! - Part 8

Last month, Roger and Ron spoke about the need for adaquate lightning protection on utility lines entering our homes and ham shacks, now picture this...

"As the ground system rises in voltage from a lightning strike, the protectors will take the ground system energy and place it on the power, telephone, and cable lines, while keeping the voltages between earth and the active lines within the limits of equipment survival. As mentioned previously, the utility ground rod for the house should be interconnected to the husky radial ground system described in previous columns. If this is not the case, the energy from the tower strike will traverse the house safety ground wires to this rod, causing problems throughout the system. Interconnecting them in the ground (using bare copper strap conductors) will reduce the inductance of the interconnecting path. House wires are a parallel path. If the interconnect path is better (lower inductance and resistance), the majority of the current will bypass the house wiring. An altemative is to provide a copper strap path through the house (difficult to fly past the XYL!). But this may not be a sufficiently low inductance path anyway (due to length needed), and it will likely radiate to other wires and equipment inside the house to boot.

The power and telephone feeds to a house can be either aerial or underground. Most hams believe that an underground connection is superior, because it provides better protection from a potential lightning strike. Although a feed buried underground will not sustain a direct hit, the amount of energy generated if a nearby tree is struck, coupled through the conductive ground medium, can be equal to a direct hit! By being underground, the wires can actually be at greater risk. The depth at which the wires are buried is also immaterial, when compared to the depth to that low frequency strike energy can penetrate.

Just a word for those who feel that they are safe from lightning because they always disconnect the coax from their equipment when it's not in use. When asked what they do with the disconnected line(s), they'll usually respond that they're simply placed on the floor. Stop and think about the last few thousand feet that the lightning has just jumped ... you can see the fallacy in this reasoning. In fact, they may make the situation worse, since arcing also involves ignition temperature plasmas inside your house. While it's true that the radio may make it through the initial lightning strike, will it survive the ensuing fire inside your home? Tossing the coax out the window isn't without its problems too, especially if the coax has already entered the house from the antenna then loops back out the window, or if the antenna is roof mounted, and without an adaquate, low inductance ground path of its own.

Grounded coax switches won't last long with direct hits either, not unless other low inductance earth-to-ground paths are provided. Remember that grounding the center conductor of the coax, and not disconnecting it's shield, can still allow large amounts of strike energy to be shared with your equipment. The coax shield connects to your equipment's chassis, and if a single-point ground is not present (along with power and telephone protectors), equipment will be damaged. Here's the point, when dealing with the amounts of energy present in a lightning bolt, thinking in terms of voltage and current levels that are normally present isn't sufficient. We have to set our thinking toward very, very large amounts of energy ... energy that's looking for a way to earth-ground. Our only effective protection is to provide that path, with as little obstruction to it as possible. That's been the thrust of the series. Try NOT to think in terms of compromise.

Ground System Materials Solid copper (wire or strap) or copper clad steel (rod), makes copper the most commonly used earthing material. A below grade ground system should be made utilizing the same base material. Mixing materials, like galvanized rods with bare copper radials, will create a battery action in which the zinc of the galvanized rods will dissolve into the soil. This will cause bare steel to rust which will not provide an optimum connection to the earth. Using stainless rods to prevent corrosion will not produce the best conductivity; since stainless steel wire would be required to interconnect the rods (remember, we don't want to mix metals), the overall resistance of the system would be increased. An all aluminum ground system should only be considered in very acidic soil conditions, and even then, the soil should be chemically tested for other aluminum-attacking soil compounds. Joints between copper radials and copper clad rods should be made by exothermic welds (see below) or by using appropriate joint compounds in high compression clamps. Soldered connections, such as torched silver solder, will not last as long as an exothermic weld.

An exothermic weld is created with a graphite mold (for the desired connection) into which copper oxide and aluminum powders are placed. An additional starter powder ignites the exuthermic process. The resultant molten copper is deposited into the lower mold cavity where it burns away any oxides and creates a larger fused connection. This larger cross-sectional bond decreases resistance and increases the surface area which reduces the inductance of the joint. Since the materials are similar, the connection lasts as long as the remaining grounding material.

High pressure clamps can produce a good bond between copper to copper because the material is malleable (soft and workable). However, average ground rods are only copper clad, with the majority of the rod being plain steel. The differences in the coefficient of expansion and contraction (with temperature changes) of the two materials, will loosen a mechanical connection over time. The use of joint compounds helps, and further enhances the weather tightness of the bond. The requisite high pressure must come from a material stronger than copper.

Ground type Rock layering within the sub-soil can make ground rod insertion extremely difficult. If layering makes it impossible to continue the insertion of a ground rod, simply cut off the the rod and connect it into the system as is (even a short rod is better than none at a given point). A rock layer will hold water and salts, which means the conductivity will be good. Making more connections to areas of higher conductivity will reduce the overall impedance of the ground system.

A ground system has a finite resistive and an inductive value. The amount and location of the inductance can reduce the overall effectiveness of radials. When a radial is placed in poorly conductive soil, the radial inductance is quite high. Conversely. when the radial runs in highly conductive moist soil, the inductance of the wire is mostly shunted by the soil's conductivity. Because copper strap has lower inductance than wire, it's been recommended throughout this series for all radial runs. The strap's extra surface area reduces inductance and the sharp edges allow for a high E field concentration (which in turn allows arcing to occur in poor or no soil conditions). We don't really care how the charge spreads out and away from our equipment, as long as it does just that!"

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 9 coming up next month.

Switch that switch!

Here's an interesting tip that you might want to try from Ken Guge K9KPM: "I think that we've all run into the problem of rotary switches becoming 'noisy' (ie., making poor contact) when left in one, single position over a period of time. It's never been completely clear to me as to why this happens; theoretically, it could be due to a couple of factors. In very low current circuits, it may be due to a minuscule degree of arcing that could be occurring, on a molecular level, which with time, eventually develops into a high resistance contact being formed. It could also be due to the contacts on the rotary switch 'taking a set' (ie., loosing some of their tension from being slightly spread apart over a long period of time). Whatever the actual reason, I believe that I've found a reasonable solution to the problem.

I own an older Yaesu FT-101E ham-band transceiver that I have in my auxiliary station upstairs in my study that I use it when it's too cool in my basement to operate comfortably from my main ham station installation. After a time resting in one position, however, the bandswitch on my FT-101E would sometimes not make good contact when I first turned the radio on to operate. Exercising the switch (running it back and forth a few times) would usually cure the problem, but taking off the transceiver's bottom cover and spraying the switch sections with contact cleaner seemed to be a more reliable fix ... until now. Lately, I've simply been placing the FT-101E's bandswitch in the 11-meter position (since I don't operate on that band position) when I'm done using the transceiver on any other ham band, then switching it back to the desired ham band when operation next takes place, some time later. Since taking up this routine, I've not had to further exercise or spray the bandswitch once, leading me to consider this practice a more or less permanent solution. Whether it's simply the self-cleaning action of rotating the switch at the beginning and end of an operating period, or the fact that tension on the switch's contacts is released during periods of non-operation is probably immaterial and more just a curiosity. The fact that this solution works for me is the important point, and so far it's been working like a charm. Now all I have to do is remember to do it!"

Moderator's note: Thanks, Ken. Potentiometers (controls) and antenna switches that are rarely (if ever) changed, may also benefit from Ken's suggestion. Why not give it a try, after all, some exercise is always beneficial!

Two for one Here's something interesting from Stephen Reynolds N0POU that you might want to try: "In case you haven't seen them, there's a new type of bass woofer speaker on the market now, one with completely isolated dual voice coils. Since the lower audio frequencies (in the bass range) don't really need to be directionalized (ie., the average person can't discern which direction bass is coming from), limited space stereo systems can usually get by with just one bass woofer or sub-woofer, located midway between the left and right higher frequency speakers. Given that, the best way to combine the bass frequencies from the two stereo channels is in a totally isolated, dual voice coil design single woofer. This keeps the higher frequencies completely separate, while nicely combining just the bass frequencies inthe one speaker. These bass woofers are usually intended to operate in the 40 to 3,000 Hz. range, so they're nicely tailored for ham radio applications (a little like a built-in high-frequency noise filter!). You can find dual voice coil woofers at Radio Shack (reg. trade mark) as well as in stores that cater to the automobile sound equipment market. For the typical ham radio application, take a look at Radio Shack's 6-1/2" #40-1373 at about $25.

Why bother with a dual voice coil speaker in the first place? Because it allows you to feed two radios into the just one speaker, with total isolation between them, but yet it will reproduce both audio sources even if they're active at the same time. If you don't have a lot of extra room in your ham shack or mobile ham installation for speakers, this method may be just what you've been looking for. It's hard to beat any two-for-one deal!"

Moderator's note: Great suggestion, Stephen. I can think of at least a couple places for a dual voice coil speaker in my own installations.

Murphy's Corollary: You can't win, most times you can't even break even, but worst of all, you generally can't quit!

Thanks to those who've contributed to this month's column, especially:

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

Ken Guge K9KPM 1107 E. Woodrow Avenue Lombard, IL 60148

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

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.