Ham To Ham #37 - October 1998

Beginning Our 4th. Year - 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

Lightning protection - what your mother never told you! - Part 10

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 9 of that series appeared last month. Part 10, the final installment, follows with this summation:

Worth Repeating Mother Nature will see to it that nothing we place in the soil will last forever. But we can do our part to design a grounding system that lasts a reasonable period of time. First, always use compatible (similar) metals in your grounding system. If copper is used, don't mix it with tin plated copper wire.

On all mechanical compression joints, copper joint compound should be used to cover the hardware. This will prevent corrosion which can cause a loss of the compression strength and increase joint resistance over time. The joint compound, a petroleum based product with conductive copper flakes, displaces water, oxygen, acids and salts.

Exothermic connections (when used) should be allowed to cool slowly to prevent stress corrosion. As explained earlier, 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 exothermic 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.

A grounding system should be tested annually. It should also be checked annually for excessive corrosion. Yes, it requires some effort, but anything less is leaving too much to chance (the very thing that we're trying to avoid).

Know your soil's pH. If it's too acidic, either correct it to neutral (using gardener's lime) or your ground system will suffer the consequences of excessive corrosion.

Selecting a protector

COAX PROTECTION: Both 50 and 75 ohm protectors are available. Most amateur applications will be for 50 ohms.

SPEED : Is the measure of protection for lightning only, or lightning and NEMP (Nuclear Electro- Magnetic Pulse) threats. Most of the protectors do well for both, but for some critical applications, higher-speed protection may be necessary.

FREQUENCY RANGE : There are broad coverage units (DC to 1.5 GHz specials) to single frequency filtered models. Today it's possible to make units to 20 GHz. Most of lightning's energy is concentrated in the lower frequency ranges of DC to 1.0MHz. The further away from this range, the less the amount of energy that will get through to the equipment (throughput energy). Always choose the lowest throughput energy for the desired frequency range.

TRANSMIT (XMIT), TRANSCEIVE (XCV) OR RECEIVE ONLY (RO): The number of XMIT signals is important (important if ham repeaters are sharing a common antenna). Protectors are voltage sensitive and multi-XMIT signals are voltage additive, not power additive. Two 100 watt XMIT signals combined equals 200 watts of treating power, but the additive voltages have peaks of 200 V, which equate to a single 400 watt signal. Because of this, multi-channel simultaneous XMIT systems must have a higher turn-on voltage and be designed to handle the peak instantaneous RF currents that can normally be reached. These are generally known as "COMBINER PROTECTORS".

TRANSMIT POWER: Each model that can support a 10 watt or higher level signal is categorized by its power level capability. Generally speaking, as the frequency is increased, the power handling rating is reduced. This is done for many reasons, the most important of which is to be sure the protector will turn off after a lightning or EMP firing, and not be "kept alive" in a glow state by the presence of the normal transmit energy. The turn-on voltage (as mentioned before) is tied in with power handling. In units that do not support DC continuity, little protection is lost by going to a higher turn-on voltage unit, especially if XMIT combining is planned in the future.

PRESENCE OF AC OR DC POWER WITH THE RF SIGNALS: This is usually relevant for "receive only" situations, such as tower-top mounted preamps. However, there are special units for the higher UHF range, and into the microwave region, for the higher current requirements of tower-top transmit amplifiers. Units are also available for DC injector/pickoff and for protecting already injected coax lines.

MOUNTING: Bulkhead panels are recommended. Flange styles may be mounted on a bus bar or on a single point ground panel. A ground strap larger than the total sum of all the circumferences of the coax shields should be used to connect to a low inductance ground system.

CONNECTOR TYPE AND GENDER: UHF style connectors are poor at the UHF frequencies (300 3000 MHz). Watt meters that use these connectors will give misleading readings even when using type N adaptors at the UHF bands. Type N connectors are recommended even though they have limited center pin lightning current handling capability when compared to UHF connectors. BNC, SMA and F male and female are also commonly found on stock protectors.

DATA/PHONE LINE PROTECTION: For lightning, twisted pair cable bundles will mutually couple surge energy to all other pairs in the cable. Unused pairs should be grounded (if allowed). Protectors are available for use on 66- type punch-down blocks with an appropriate grounding bus. For 6 pairs or less, more energy will be present per pair, so a hybrid protector that can handle energy levels that would normally vaporize standard 24 AWG wire pairs should be used. Selection of data/phone line protectors depends on the presence of either -48V battery and/or ringing voltages. The line impedance and total allowable loop resistance (as well as the highest frequency or bit rate), will determine the insertion loss from the protector's IO line resistance/inductance and capacitance.

POWER LINE PROTECTION: For lightning and EMP, shunt type protectors will limit the voltages to a safe level for most non-electronic equipment. In-line type protectors are mandatory for electronic equipment survival. These in-line units should be mounted/grounded close to the equipment being protected. For mainframe computers and high-power RF equipment, in-line power mains protectors are produced which provide single or polyphase protection with EMI/RFI filtering. They'll often have front panel status lights and local/remote alarm contacts as standard equipment.

For power line protector selection, the peak voltage, number of phases, configuration, and in-line current usage, will pinpoint the unit best suited for a particular application. Voltages to 480Vac are readily availabe for single to three-phase applications. Replacement modules and breakers are usually available separately for most models.

The Big Bertha - Lightning Simulator Our quest for knowledge has taken us to the point of actually making a lightning simulator that couldn't be purchased. We lovingly call it "Big Bertha", and it consists of ten 200 microfarad capacitors, which have a total weight of three quarters of a ton! Not your typical table-top high- voltage insulation tester! The simulator is set up as a "Marx Generator", which means that the capacitors are charged in parallel and then connected in series for the discharge phase. This is the most straight forward way to get 100,000 volts delivery with 62kA and 100,000 Joules of energy.

Delivery to what, you may ask? An antenna, of course.

To start with, we thought that we needed to know more about the effects upon and the output from an antenna when it gets hit by the real thing, lightning. We'd already tested transmission lines and knew how they share strike current with the tower, but we had no idea what the different antenna designs would have on the current waveform. Some of the questions that we needed answered were: 1.) Would the antenna ring, and if so, for how long? 2.) What voltages would it reach? 3.) What effect does bandwidth have? 4.) How much energy is coupled to a side mounted antenna when the tower is hit? 5.) What are the effects and pick-up patterns from nearby strikes?

It's and on-going project, and we hope to have some results of tests from donated commercial antennas shortly. The aim is to provide commercial antenna manufacturers with real-life survivability data, with the goal in mind of permitting them to build better antennas from a lightning survivability standpoint (and not just an RF transmission standpoint). It would also be advantageous to the industry to have a standardized lightning survivability testing scheme, so that the end customer can factor an antenna's lightning resistance into the purchasing formula. Perhaps the realization of this goal may yet come out of our research.

If funds permit, we will also be working, together with the University of Nevada (and Big Bertha), on testing and learning more about the glassification of ground rods and on arcing in and out of the earth/rock interface. This knowledge will be helpful for developing even better grounding systems for use in poor soil conditions and for rock-encrusted mountain top sites ... and so the research continues.

We hope that you've enjoyed learning from this series of columns on lightning and its effects on nearby electronic equipment, and that you've gained some valuable information on how you can protect your own home ham station (or repeater station) from lightning-originated damage. From the information this month, and previous from columns, you can see that effective lightning protection isn't as simple as just a ground rod and a spark-gap arrestor. For state-of-the-art protection, a well planned and mechanically sound lightning diversion system is essential for maximum survivability of your equipment. It's recommended that you go back over the previous columns since the Janauary 1998 issue and refresh your memory from time to time. It can take a while to become adept at thinking in lightning protection terms in everything that you do with your antenna and station ground construction and maintenance, but once you do, it can pay very big dividends. Let us know if you enjoyed the series.

Moderators note: If you missed any installments of this series by Roger and Ron Block, you can contact PolyPhaser Corporation by telephone at (702) 782-2511, at: http://www.polyphaser.com/ on the web or at (702) 782-6728 for access to their telephone BBS. Ask for a re-print of their special bulletin "Protection to Keep You Communicating". This month's treatment concludes the series by Roger and Ron ... we sincerely thank them for their generousity in the sharing of this hard-won information with us via the pages of 73 Amateur Radio Today Magazine. This concludes the series "Lightning protection - what your mother never told you!"

Homebrewing at its best!

In this suggestion, Mike Hall KE4GBE, explores some of the possibilities for recovering otherwise discarded NiCd battery packs: "Each month, thousands of rechargeable batteries are bought for cordless phones, often unnecessarily. Consumers will many times replace the rechargeable batteries in their cordless phone, simply because it's the easiest thing do when a problem with the phone arises, or because they've received poor advice from someone, even though there may have been nothing wrong with the batteries to begin with.

Radio Shack (reg. trade name) and other NiCd battery dealers now offer a recycling service to their battery customers. Since disposing of NiCd cells in landfills is not environmentally responsible, recycling depleted NiCd batteries makes good sense, but often the cells that end up in the recycling bin are still very much usable. It can pay you to make friends with the store manager at one of these retail battery outlets, so that he or she will permit you to take some of the packs home for testing and possible further use. If you promise to return any unusable cells for proper recycling, and return the currently operational cells once they've been used up, then there's really very little reason why the manager won't go along with the idea. Personally, I've found that roughly one third of the battery packs that I've obtained by this method are still serviceable. Sometimes the entire pack is okay, other times just one cell is bad. In either case, I've been able save quite a bit of money on new NiCd batteries just by following a few simple procedures.

Most of the cordless phone packs consist of three (3), 280 milliampere cells wired in series. As shown in Chart 1, a potentially usable pack should read about 3.6VDC, perhaps a bit more when just freshly charged. When you've located several good 3.6 volt packs, cut off the connector, leaving about 1/2" to 3/4" of the original pack wire still attached. Try topping off the charge on the pack using a safe, one-tenth capacity charger (28 MA) for 12 to 14 hours. Now discharge the pack at a fixed current and see how long it lasts. If you can get close to the rated 280 MA capacity, you know that the pack is worth saving. Your exact end results can vary somewhat, so it's something of a judgment call. Mark the pack with your findings so that you'll know which pack delivered what amount of energy later on. A 280 MAH pack should deliver about 280 milliamperes for one hour, or 140 milliamperes for 2 hours, etc. Once you've salvaged several packs, then you're ready to build a larger, higher voltage, higher capacity super-pack!

Again following the figures in Chart 1, if you need a pack to power a 12 volt DC QRP rig for instance, 4 of the 3.6 volt packs wired in series will give you 14.4 volts (about what an automobile battery delivers when the car is being driven and the alternator is replenishing the battery). To increase the current capacity (ampere-hour-capacity) of your super-pack, you can wire additional series-connected 14.4 volt 280 MAH packs and then put all of the packs thus wired in parallel. Each time you add another parallel group, you increase the overall ampere- hour-capacity by about 280 milliamperes. I have one super-pack that contains 32 of the original 3.6 volt packs, that is, 4 packs in series for 14.4 volts, then 8 of these 14.4 volt packs in parallel. This 32-pack battery will deliver roughly 2-1/4 ampere hours of energy, and it was virtually free! With it, I've been able to run my CW QRP rig for about 2 hours (at 1.5 amps average drain).

It's best to charge the series-connected packs individually, but that only requires 8 current limiting resistors, and eight silicon diodes, fed by one charger capable of delivering about 20 volts at 250 MA. Figure 1 shows the basic schematic diagram for such a simple charger using a readily available "wall wart" power cube. It's about as basic as a reasonably constant-current charger gets, and of course, feel free to improve upon the design to make the current delivery even more 'truly constant' if you wish.

So there you have it, you can help out the ecology and save money at the same time ... to me, that's homebrewing at its best!"

Moderator's note: When connecting several NiCd battery packs in parallel, it's a good idea to also place a silicon diode (such as a 1N4001) in series with each pack's positive output lead (see Figure 2). This added diode prevents the tendency of unequal packs to "charge" one another during use. More importantly, if one of the packs should catastrophically fail (ie., short), it will prevent the good packs from feeding the short and draining themselves at a high rate of current. A small potential will be dropped across the diode (about 0.7V), but it's worth it for the added reassurance. Remember that a separate "charging" wire is needed, however, to by-pass around the diode when recharging the pack. The pack will now have 3 wires coming from it ... one positive wire for charging, one positive wire (with the diode in series) for parallel operation and the remaining common (or negative) wire.

1 NiCd cell = 1.2 volts

2 NiCd cells = 2.4 volts

3 NiCd cells = 3.6 volts

4 NiCd cells = 4.8 volts

5 NiCd cells = 6 volts

6 NiCd cells = 7.2 volts

7 NiCd cells = 8.4 volts

8 NiCd cells = 9.6 volts

9 NiCd cells = 10.8 volts

10 NiCd cells = 12 volts

11 NiCd cells = 13.2 volts

12 NiCd cells = 14.4 volts

Chart 1

As shown in Chart 1, each good NiCd cell should read 1.2 volts DC when it has taken a proper charge, so it's relatively easy to determine if a pack has all good cells, or just if one of its cells is defective. By the way, a fully charged NiCd cell will actually read 1.4 volts DC when it just comes off the charger, but will then fairly quickly drop to the 1.2 volt figure shown in Chart 1 under load. A good cell should also hold closely to that 1.2 volt figure for the bulk of its usable charge-life (before it needs recharging). If a cell reads zero, then it's usually shorted internally. If it reads less than 1.2 volts, or drops significantly below that figure under load, then it has an exceptionally high internal resistance and shouldn't be used. And please remember to properly dispose of all of your dead NiCd cells at an apporved recycling center

The 5-Minute Bandspread!

If you're the proud owner of an older receiver or transceiver that you would still like to get more use out of, then maybe this suggestion from Bruce Cameron WA4UZM will appeal: "One of the biggest drawbacks to many older ham rigs is their tendency to tune too fast, even if they have some sort of mechanical vernier gearing built into them. Newer ham transceivers, with digital electronic tuning, offer a veeeery slow tuning option, but here's something that you can try on your older rig without spending a fortune or investing hours of modification time.

Just remove the present tuning knob from your radio and make a trip to your local medical supply store. There you'll likely find replacement rubber tips for use on crutches, canes, walkers and other mobility aids. These replacement tips will often fit nicely over the current tuning knob on older equipment (just bring the knob along), giving you the basis for implementing the rest of this idea.

Once you've located the right crutch or walker rubber replacement tip, insert a stiff piece of piano wire, that's been sharpened to a point on a grinder or with a file, into the rubber tip as shown in Figure 3. By the way, stiff piano wire can usually be obtained at any well-equipped hobby shop in town or you can simply use a small section of a wire coat hanger. You may also want to put a tiny dab of glue or epoxy around the wire to keep it firmly in place. The wire needs to protrude out of the crutch tip only 2 or 3 inches, short enough so that it clears the desk below when the knob is rotated. That's all there is to it! The new tuning knob cover with its protruding wire gives you the extra 'lever-arm' needed to make your old fast tuning action considerably more 'vernier' in feel and in action. Give it a try and you'll see what I mean."

Murphy's Corollary: In crisis situations, which force us to choose among alternative courses of action, most will lead us on the entirely wrong course!

As we begin the fourth consecutive year of the Ham To Ham column in 73 Magazine, we offer a very special thanks to this month's contributors, including:

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

Mike Hall KE4GBE 8131 Browning Circle Ackworth, GA 30101

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.