Note: If you would like a copy of any of the circuit diagrams
or figures referred to in this column, simply send a SASE to:
73's Ham To Ham Column
c/o Dave Miller NZ9E
7462 Lawler Avenue
Niles, IL 60714-3108
and indicate the month and circuit or figure name on your request.
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Ham To Ham #32 - May 1998
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. So far in this series (which began with the January 1998
issue), Roger and Ron Block have given us some interesting lightning statistics, talked about antenna location, the importance of a single point ground system and how to install an effective underground radial system to dispurse the energy in a strike safely, what shape and size ground
conductors are best to use, soil doping, ground resistance measurement, how to handle dissimilar metals, how to minimize pickup of radiated energy from a lighting strike, how to protect your coax and rotor control cabling, and some tips on protecting utility lines entering and exiting your ham shack (and home).
This month they continue the series with some technical considerations on selecting I/O protectors, locating the ham shack itself with the consideration toward minimizing the effects of a lightning strike, and some more hardware tips that the pros use when designing lightning-
minimized tower installations. This series will continue through the remainder of the year in short, easily digested segments and our sincere thanks to Roger and Ron Block for sharing their expertise with 73's Ham To Ham column readers.
If you'd like to see the original, unabridged version of Roger's and Ron's work, 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.
Part 4 of the series was presented last month, part 5 now follows:
Lightning protection - what your mother never told you! - Part 5
No Sharp Bends
When dealing with grounding systems for lightning protection, be sure to route all ground straps and grounding conductors to form a gentle bending radius. Bends sharper than a one inch radius will add unwanted inductance to the desired ground path. Sharp bends should not be used even
for conductors that are buried underground.
Coaxial Protectors (some technical considerations)
Coax protectors should have dc blocking on the center pin, ie., they should show an "open" to dc current (such as when measured with a typical ohmmeter). This serves as a form of high pass filtering, which prevents the dc, and the low frequency energy of lightning, from continuing on to toward the equipment. The strike energy is diverted into the ground system instead, in a controlled, predetermined fashion. This dc blocking also ensures the operation of the protector regardless of the input circuitry of the equipment being protected. Since lightning is mostly of the same polarity, protectors (or even RF equipment with ferrite core material inductors to ground) will
carry enough surge current from a strike to saturate those cores. Over time, the ferrite material will therefore become "oriented" and will no longer be "random". This is the primary reason why isolators often have less "directivity" over time, and become lossy. Protectors using ferrite coils
prior to voltage crowbar gas tubes will also experience a VSWR degradation with repeated hits.
Protectors with dc continuity will not work on receivers and shunt-fed duplexers. The shunt-to-ground inside a receiver (the input coil to ground for static draining) prevents the low frequency lightning from being conducted safely to ground by a protector having dc continuity. Here's what
happens, the coil in the receiver shunts the energy to ground, but at the wrong place. If the coil can not handle the energy (half the coax surge energy is on the center pin), the coil will open and the current will translate to a large, open voltage source capable of arcing anywhere within
the radio. The best protectors dc block both the center pin energy, and the shield energy, from the equipment, thus preventing shield energy from continuing to the equipment chassis. If the "withstand" voltage (shield protector turn-on level) is exceeded during a strike event, and if a
proper single point grounding system is in place, the voltage on the shield to the equipment will not exceed I0kV.
Ham Shack Location and Protection
A basement is an ideal location for a ham shack. It's close to ground and generally has the lowest inductance run to the ex terior grounding system. Because it's below grade, magnetic shielding may also occur naturally. Most basements, however, have concrete floors, and since concrete is
considered a conductor, the equipment must not sit directly on the concrete floor. In the event of a strike, surge energy could enter the shack and seek out a ground path through the equipment and to the floor. Insulate the equipment with a material that does not absorb water (a material that
won't become hydroscopic from water or even mositure in the air. Polypropylene is a good choice for a full footprint sheet insulator.
The first floor of a building is the next best location for your ham shack location. Just remember that magnetic shielding may be less, and the inductance to the ground system may be higher, (due to a longer ground strap run). If the tower is located very close to the building, the
recommended grounding strap (running from the exit point and down the building's outside) may itself inductively pick up some energy from the tower. This is also true for the coaxial cables, cabling for any tower lights and rotor lines. The longer the parallel run with respect to the tower,
the more energy will be coupled. Protect these lines at the tower base utilizing an EMT steel conduit. The conduit should be grounded to the equipment ground end only, and will act as a Faraday shield for the cables inside of it. If the tower is somewhat further from the building, it will
be necessary to provide protection at the tower, for all lines, as well as having protection inside the shack itself. In this case, ground the conduit to the tower end only. Do not run any unprotected lines in the EMT. Protectors must be grounded to each other and to the tower ground. Place the
protectors inside of a weatherized NEMA (National Electrical Manufacturers Association) approved box, such as a NEMA 3R or NEMA 4X. Make sure the weatherized box and inside mounting plate are properly grounded (removing the paint from the box's outside and inside surfaces at the ground point) and use the correct joint compounds to weatherize all connections. Stainless steel
hardware is also an option. All connection lugs must be crimped, soldered and weatherized. Remember, standard 60/40 solder will not hold up when exposed to sun light and ozone ... without protection. If possible, try to use 96% tin and 4% silver solder, it has more strength and will handle
high surge currents because it's specifically a high temperature formulation. Use a short section of strap or a husky pigtail to bond between the inside surface of the NEMA box and the inside protector mounting panel. Ground any conduits at the ground level. Again, use the proper joint compound prior to either a vertical run or an entry into the building. Good mechanical and
electrical connections don't just happen, they're based on experience within the trade and are well thought out and planned.
Roger and Ron Block's series will return again next month with more of what mom never told you on how you can best protect yourself, and your station, from the destructive effects of lightning. This ongoing series in the Ham To Ham column this year is "must" reading for everyone who spends any time stretching conductors in the sky (and in the ground) in pursuit of that elusive rare one.
A "T" for Top Band
Here's a modification that you might want to consider from Tom Hart AD1B: "One of the more popular wire antennas for the HF bands has been the venerable G5RV dipole, a classic antenna that operates well from 80 through 10 meters in its normal configuration. I've been using the G5RV myself for a number of years, all the way up to 6-meters, and have logged nearly 2,000
contacts with it on the RS-12 satellite to boot!
On 160-meters, however, the G5RV (being horizontal), generally produces rather poor results, since most of us can't get a dipole style of antenna up in the air nearly high enough to obtain a good horizontal launch angle at 160-meters ... most of the signal ends up going straight up! Even at 40 ft. up, a horizontal dipole at Top Band (160-meters) is only .08 wavelength above the ground, which would be functionally equivalent to putting your 10-meter dipole just 3 feet off the ground! Successful 160-meter operation, therefore, generally involves using a vertically polarized antenna, but unless it uses a large and lossy loading coil, it too will be extraordinary tall ... 150 feet or better!
Wanting to operate some 160-meter contests and other occassional get-togethers, I decided to try some simple (and easily removable) modifications to my own G5RV ... and a top-loaded "T" configuration is what I found the easiest to implement. Additionally, it does a reasonably
respectable job for a 'compromise' Top Band skyhook! What follows is what I've found to work nicely at my QTH and should be adaptable to others.
By the way, an earlier version of this idea was described in CQ Magazine some years back, but this latest configuration seems to give better results (at least subjectively) at a very small additional cost in terms of set-up time and materials ... remember, this is a temporary, stow-it-away-when-you're-
not-using-it modification. The main addition is the Adapter Shorting Box shown in Figure 1. It's nothing more than a way of connecting the shield and center conductors of the coaxial downlead from the G5RV dipole together ... shorting them together if you like. This turns the center-fed G5RV dipole into a top-loaded or "T" type of vertical radiator. Next, two counterpoise
wires (or radial wires), each 165 feet long, are added to the base (adapter box) connector that eventually connects to my transmatch (antenna matching unit) back in the shack. The two 165 foot counterpoise/radial wires are wound up onto a section of cardboard tubing, and unwound and laid-out on the ground when I want to configure my G5RV for Top Band. Most of us can't unwind 165 feet of wire in a straight run, and neither can I, so the counterpoise/radial wires end up making something like a large "S" shape on the ground ... but the wire is still out there. To help keep the
counterpoise/radial wires in place, I've made up several 6" lengths of wooden 2 x 4 section 'anchors', each with spring-action wooden clothes-pins glued and nailed to the 2 x 4's. I place one of these 'anchors' at each bend in the counterpoise/radial run to keep the wire from being blown or kicked around while it's out and in-place. The 2 x 4 and clothes-pin anchor scheme is shown graphically in Figure 2.
That's basically it ... I've found that the G5RV, configured as I've described, and operated via a transmatch in my shack, will give me a usable bandwidth comparable to what I'm able to achieve with the 'stock' G5RV antenna on 80-meters ... not bad! The estimated vertical radiation pattern is reasonable as well, and Figure 3 gives you an idea of what you might expect if you decide to duplicate the idea. Again, my original goal was to be able to operate on 160-meters, with a usable signal, primarily for contests and other short duration work, without the need to erect a dedicated
Top Band radiator. By using this technique, and the information shown in the ARRL Antenna Handbook and published by ON4UN, I ended up with a satisfying compromise antenna with very little effort and cash outlay. Give it a try at your own station.
Fuse Tale
Here's a QuikTip from Bob Boehm N8EXF: "After struggling trying to remove the tiny GMA style fuse, mounted on the printed circuit board of my Kenwood TS-50 after it opened, I decided to make my life a little bit easier the next time that fuse might give out. I cinched a small nylon cable tie around the new fuse's body, leaving enough "tail" on the cable tie for me to easily grab it, before replacing the fuse in it's clips. The cable tie's "tail" will make the chore much easier, if and when the tiny fuse needs replacement in the future. Of course you can adapt the idea to any small cartridge style of fuse in any hard-to-reach location ... a short tale, but true!"
Not quite what the doctor ordered
Here's a way to get more for your prescription dollar from Harold Proppe Jr. K6QVD: "Now that I'm a senior citizen, I've discovered the 'advantage' (?) of having lots of empty plastic prescription pill bottles to dispose of! In addition to storing small parts, they have other uses in and around the
ham shack. If you need a quick coil form (Figure 5) or a light-weight dipole antenna insulator (Figure 6), a pill bottle will often be just the ticket. They're also useful as small containers for holding tiny circuits (for interfacing one gadget to another) or perhaps enclosing a switch or jack for
this and that purpose ... and because they come in many varied sizes, keeping a stock of them on hand will usually produce the one that's just right for the project in mind."
Moderator's note: It's easy to test a pill bottle's RF insulating qualities if there's any question of it's propriety for use as a coil form or insulator as Harold suggested. Just place it in a microwave oven for 60 seconds or so, along with a small glass of water to act as a known load, and see if the pill bottle gets hot to the touch. If it doesn't, you know that it's RF transparent. Ultraviolet light can also disintegrate many plastics, so before using an unknown plastic as a permanent outdoor antenna insulator, set one outside, exposed to the sun for a while, and see how much it's
adversely effected. For indoor or attic antennas, UV susceptibility isn't a concern.
Murphy's Corollary: The furthest distance between two points is usually the short-cut.
And many thanks, as always, to this month's very much appreciated supporters, including:
Roger Block, President
PolyPhaser Corporation
2225 Park Place
P.O. Box 9000
Minden, NV 89423-9000
Thomas Hart AD1B
54 Hermaine Avenue
Dedham, MA 02026
Bob Boehm N8EXF
6821 Le Conte Avenue
Cincinnati, OH 45230-2935
Harold L. Proppe Jr. K6QVD
1385 Skyline Drive
Laguna Beach, CA 92651
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.
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