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.
No requests will be honored without a self-addressed and adaquately
stamped reply envelope (SASE).
========================================================================
Ham To Ham #31 - April 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
Despite the fact that this is the April issue, there's no foolin' in this month's Ham To Ham column ... just good, practical suggestions! By the way, if you have any that you'd like to see printed in a future issue, all you have to do is jot them down and mail (or e-mail) them to me at either of the
addresses shown above. I'm always looking for more practical tips and ideas to grace these pages, so don't be shy. There's a lot to cover this month, so let's get right to it.
First in line, 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 destructive effects of a lightning strike. Part 3 of that series was presented last month, part 4 now
follows:
Lightning protection - what your mother never told you! - Part 4
Coax Grounding
Since the tower is a conductor, and is well grounded, all tower coax lines should be grounded (using approved grounding kits) at the top of the tower, close to the antenna, and at the base of the tower, before they head toward the indoor equipment. During a strike event, the tower and the coax lines will mutually share the strike energy. If the coax lines are not grounded as they leave the tower, or worse yet, they are completely isolated from the tower, more energy could traverse the coax cabling toward the equipment, than is conducted to the ground system by the tower. This large inductive voltage drop may cause arcing between the coax lines and the tower, which could
cause coax deterioration (pin holes in the coax jacket for moisture to enter later) or even complete destruction of the coax lines.
Since all towers have some inductance, leaving the tower at a point above ground will allow some of the strike current to continue on the coax line (both the center conductor and shield), and on toward the indoor equipment. If this current is allowed to reach your ham shack, it will follow the chassis to the electrical safety ground, raising the voltage levels in the cabinets to deadly magnitudes. Remember that inductive drop!
Even though the inductive properties of the coax cable appear to be beneficial, and some extra inductance can be created by adding a few turns to the coax cable, it is not normally recommended. The added turns can act like an air wound transformer, which can actually couple more energy into the line (via radiated pick-up). This obviously, is opposite to the desired
effect. Additionally, the coax lines leaving the tower should remain at right angles to the magnetic field surrounding the tower for the least amount of magnetic coupling possible.
Rotor Control and Coax Line Protection
Rotor control lines should be protected using a suitable protector at both the top of the tower (where the lines enter the rotor motor), and again, inside the shack at the single point grounding panel. If it's not practical to protect the lines at the single point grounding panel, protect them at the base of the tower, then run them inside EMT (Electrical Mechanical Tubing or
conduit), grounding the conduit only at the tower base. The EMT conduit will act as a Faraday shield from the tower's magnetic fields, minimizing the amount of induced energy. Coaxial RF lines can also be protected from induced energy using EMT conduit, and again, grounded only at the tower base (see Figure 1 for some ideas on how to accomplish this).
The Single Point Grounding Panel
The next step in any good lightning protection scheme is to provide a single point grounding panel, a plate upon which equipment I/O protectors can be located. The panel is best located near the main system ground, again, in order to keep the inductance of the earth ground conductor low. However, if this would require that the panel to be too far from the protected
equipment (more than 10 feet), and if the magnetic fields of a nearby tower could easily couple into the interconnecting wires and cables (after the single point panel), then the panel should be located closer to the equipment. An alternative (although not as good) to the single point
grounding panel might be a dedicated equipment rack panel (if the station equipment is located in a standard equipment rack as is often found in an amateur repeater installation). This is recommended only if all I/O protectors are mounted on the panel and the earth ground connection is directly to the panel and not via any other piece of equipment. Grounding the panel is essential and only copper strap should be considered. Since the strap is flat, its susceptibility to induced magnetic fields is only with respect to its thinner edges. To prevent coupling, the strap should be
positioned with the flat side parallel to the tower (the most likely strike point and source of a strong magnetic field). The single point grounding panel should be positioned so that its flat side parallels the tower for the same reason as mentioned for the earth ground strap. Direct grounding (with a heavy conductor) of each individual piece of equipment in a rack is essential if the equipment rack rails are painted (as is usually the case). Painted rack rails afford little in the way of an adequate ground when only part of the screw threads are actually touching ground. Figure 2 illustrates one approach to a single point ground when rack mounted equipment is involved, Figure 3 shows how it might be accomplished for a desk-top installation. Each installation is different, so you'll have to adapt these examples to your own unique setup. But of greatest importance, is understanding the basics, and always keeping those basics in mind when you set about to protect your own ham shack and tower installation.
In the operating or equipment room, each piece of equipment must be bonded to the single point grounding panel with a low inductance copper strap. This will maintain all chassis potentials at the same level during a strike event, as well as minimize chassis-to-chassis current flow. The power, telephone and coax line protectors on each of the I/Os (equipment input/outputs) must be
mounted on the single point panel as well. This will minimize I/O-to-l/O current flow.
Additional protectors should be used to safeguard the feed point or entrance locations for the power and telephone lines. These will provide added protection for jointly used equipment such as answering machines, appliances, etc. Ideally, they should also be grounded and connected by a buried, bare conductor to the ground system.
Surge energy can enter a shack in two ways: from a strike to the power or telephone lines, or from a strike to the tower. In either case, high quality protectors will divert the energy into the ground system. Because of varying propagation delays of your ground, if the protectors are electrically separated from each other by a considerable distance, they cannot work in unison to keep the voltage levels between the equipment I/Os within a tolerable range for predictable equipment survival.
Moderator's note: Some of the preceeding suggestions may seen like overkill, but please bear in mind that when we speak about lightning, we're talking about an extremely high voltage, high current event of nature. Even small resistive or inductive drops can cause huge voltages to be developed ... especially in view of the very low voltages that our modern solid-state equipment is designed to tolerate. But much more important that the equipment to be protected is the life and well being of the operator ... you! Roger and Ron Block's series will return again next month with more of what mom never told you about lightning and how you can best protect yourself, and
your station, from its destructive effects. This ongoing series in the Ham To Ham column this year is "must" reading for everyone who searches the ether in pursuit of that elusive rare one, whether you're a ham, SWL or general electronics enthusiast.
Tape tricks
Here are a couple of uses around the ham shack for plumber's Teflon (reg trade mark) thread-sealing tape that you may or may not have thought about.
I've found that at times, plumber's Teflon tape can be used to bail me out when I've accidentally goobered-up the threads in a plastic housing, and the screws just turn freely when I try to snug them up. Wrap several layers of Teflon tape around the screw threads (in the area shown in Figure 4), and reinsert the screw into the stripped hole. Tighten it down fairly snugly, but not too tight, and the screw may just recover enough "grab" to begin to do its job again.
A wrap or two of Teflon tape around the threads of a PL-259 / SO-239 coax connection that's going to be used outside, will help to keep moisture from getting into the connection (just as it prevents water from leaking out in its normal use on plumbing pipe threads). In fact, you might want to try wrapping the entire connection with the Teflon tape, then follow up with whatever sealing method you normally use for exterior coax connections (electrical tape, liquid plastic-dip, black coax sealing putty, amalgamating tape, etc.). Since the Teflon plumber's tape is very thin and stretchable, it can usually be prodded into covering-up even irregular forms and shapes that need to be protected from the ravages of the elements.
Teflon tape wrapped around the threads of screws and bolts that are going to be used out-of-doors, will sometimes help in preventing them from oxidizing and corroding-in-place as much as they otherwise would. If a thin, but reasonably complete, insulating and protective barrier can be
established, electrolytic and chemical degradation of ferrous metals used outside can be slowed down (though perhaps not prevented entirely). Even just wrapping the exposed threads of a bolt being used outside will help make that bolt a little easier to remove when the time comes for disassembly; again, enlisting the tape's uncanny ability to conform to irregular shapes that need this outdoor protection.
Give some of these suggestions a try ... you'll no doubt find many more that I haven't thought of. If you do, jot them down and send them in to me for a future Ham To Ham column follow-up piece.
Dave NZ9E
Bigger is better
Here's a neat idea from Stan Strasburg W5TPS: "Photo 1 shows the setup that I've been using to help me to read the 'smallish' print normally used in magazines and on many schematic diagrams, as well as to continue to work on my ham and electronic gear ... a pass time that I love. I have a degenerative eye condition that doesn't permit me to see clearly any longer (particularly small objects) in their unmagnified state, but as you can see from the photo, that doesn't have to stop a person from enjoying his/her hobby and its many facets.
The setup is easy to duplicate using today's electronics ... just use a 23" or 25" color TV set with a "Video Input" option (most will have a video input these days), and a light-weight, color, miniature, all-solid-state (CCD) TV camera. Mount the CCD TV camera on a spring-loaded light arm (the type of arm that's used for most auxiliary clamp-on bench lights), and you're pretty much done! It's usually not too difficult to rig up an 1/4-20 adapter stud arrangement for mounting the light-weight camera to the light arm, but if mechanical work isn't your cup of tea, or you can't see well enough to do it yourself, perhaps a friend who is handy with tools can help. Figure 5 shows
one such arrangement in a bit more detail, but the actual modification needed will most likely vary somewhat from one brand of bench light arm to another. You may have to be just a bit 'inventive' here.
The little solid state TV cameras today generally don't require any additional lighting to produce a very usable picture on a large-screen monitor, but if needed, a small high intensity desk lamp will probably provide enough extra boost in light level. Of course the end idea is to electronically magnify very small objects (or printing), to a format much more large and bold for those of us with sight deficiencies. The little camera on the adjustable arm is so versatile, that almost nothing is
'out-of-sight' for me any more!"
Moderator's note: Great suggestion Stan. This idea can open up a whole new world of enjoyment to those with a visual challenge ... if not yourself, perhaps a friend or neighbor might benefit from Stan's idea. But even if you don't have (or know of someone) with small-detail vision problems, the basic idea can be put to work for you when you need to "surgically intervene" on
some of today's ultra-miniature circuit boards! Operating room surgeons are using similar techniques to help them to see what they're working on when delicate surgery is being performed, and we can all duplicate the concept (for a whole lot less money), with just a little time and innovation. If you opt to use one of the very small (and light-weight) CCD 8mm camcorders
on the market today, you can also video tape a complex disassembly procedure, so that putting everything back together again later will be made considerably easier. There's lots of room for individualization here!
A well grounded idea!
Check out this idea from Herb Foster AD4UA: "Here's a simple, inexpensive and easy-to-add-to suggestion for how you might be able to implement an effective, single-point ground bus on the back of your amateur radio desk ... I've been using this method myself for some time now.
Simply purchase a length of 1/2" copper water pipe, as long as your operating desk is wide. Clean the length of pipe thoroughly, so that it looks nice and shiny. Kitchen cleansers, steel wool and fine sandpaper can all be enlisted to help with this part of the job! Now screw down the shiny pipe, with a husky screw and 1/2" spacer, thru each end of the pipe, to the back (top)
surface of your operating desk. The spacer can be made of any material, even a couple of small chunks of the 1/2" water pipe itself. The spacer's job is to hold the copper-water-pipe-ground-bus 1/2" above the operating desk, so that you can then feed any number of 1" stainless-steel hose clamps around the pipe as the 'tap points' on the bus. All of your equipment ground wires
will now go to the hose clamps and be rigidly clamped directly to the copper pipe, but yet easily removed or relocated should the need arise. Of course a main station ground strap will also go from the copper pipe bus directly to your earth grounding system; Figure 6 gives you an approximate idea of what the finished product will look like. You should be able to accommodate
dozens of these small clamps on the ground pipe, so that your new operating desk ground bus will never be out of tap-off points."
Moderator's note: Nicely done, Herb. This is probably one of the easiest-to-accomplish ideas that I've seen for fulfilling the requirement of a solid, separate-wire earth ground for each piece of gear on your desk. Also, take another look at Figure 3 as previously recommended by Roger
and Ron Block.
Murphy's Corollary: Any transistor, protected by a fast-acting fuse, will blow-out first, thereby protecting the fuse.
Many thanks as always to the contributors to this month's column, including:
Roger Block, President
PolyPhaser Corporation
2225 Park Place
P.O. Box 9000
Minden, NV 89423-9000
Stan Strasburg W5TPS
1516 W. Magnolia St.
Rogers, AR 72758
Herbert L. Foster, AD4AU
3020 Pennsylvania St.
Melbourne, FL 32904-9063
e-mail ad4ua@juno.com
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.
End of file