Ham To Ham #9 - June 1996
73's Ham To Ham column
c/o Dave Miller, NZ9E
7462 Lawler Avenue
Niles, IL 60714-3108
In last month's column, Robert Blacka, N2WSO offered a good tip on a line of "camouflage" rope offered by The Lehigh Group of Allentown, PA; since then, I've received their well-laid-out catalog of cordage and accessories, and the rope that Bob mentioned seems to be Lehigh's item # CF450 (the number mentioned in the column last month may be the dealer's stock number along with a UPC code). It's described as twisted polypropylene rope and is said to hold knots well, resists oil, gasoline and most chemicals, is resistant to rot and mildew and it floats (hopefully not needed in ham radio applications!). The standard length is 1/4" by 50 feet and comes with an instruction booklet outlining its proper use and care as well as knotting and splicing methods. Lehigh's phone number is 1-610-398-1830...their catalog is worth having for general information on cordage and fittings.
Pin-point it with a laser
We've all hear the expression "a solution looking for a problem". That's what I had considered the abundance of those new "pocket laser pointers" to be...seems everyone is offering them...until I thought about it some more. The pen-sized pocket lasers points are advertised as being useful for large group presentations, and they no doubt are, but how many of us give large group presentations often enough to justify the purchase of one? No question, they'd be fun to "play" with (just don't look at it or it's mirrored-reflection directly), but I needed a bit more incentive than that to spend the money necessary to actually buy one. Well, for those of you who are in the same predicament, here's the justification you've been looking for, and it's an very useful one.
It's often fairly easy to locate the correct component for replacement on the component-side of a printed circuit board, since the part numbers are generally silk-screened on that side, but locating the proper pads to unsolder on the foil-side of the board is another matter altogether. That's where the little hand-held laser pointer comes in.
Simply hold the laser pointer over the correct component, on the component side of the board, and then looking at the foil side - perhaps with the room lights dimmed a bit - you'll be able to see the exact point to unsolder. It's particularly useful with phenolic PC boards, but it even works on the heavier fiberglass boards (though the light does scatter a bit more depending upon the density and "grain" of the board material).
If you'd like to drill a hole through a plastic case, but you'd also like to see where it will end up on the other side of the case before you drill, the little laser pointer's light will even penetrate some of the less-dense plastics. Too bad it doesn't penetrate aluminum...or even drill the hole for you...at least not yet!
Finally, our two younger cat loves to chase the "red dot", though be careful not to shine the pointer directly into your own or your cat's eyes; again, intense laser light can be dangerous if misused. Lasers derive their pin-point energy by forcing all of the photons to march in-step, at exactly the same color frequency and in exactly the same direction - much like a well-drilled military marching unit. By the way, our older cat shows some - though dignified - interest, but apparently he considers the laser pen just another variation on the old "dancing-flashlight-beam game"!
These are my contributions, what problems have you solved using this lastest "solution looking for a problem" device? Send me your ideas - at the address in the masthead - and I'll compile them for a future column on "sharp-laser-pointer-tips" - pun intended.
DE Dave, NZ9E
A strapping-good idea
This suggestion from James Brown, AE4EY of Florence, Kentucky is certainly worthy of
consideration. He writes: "My shack is located in the basement of my home, and the closest
nearby ground is the cold water pipe running through the rafters about 5 feet above my operating
position. In the past, I simply used wires from each piece of equipment, joined together at one
connection-point, then a single wire running up the wall and to the cold water pipe. The final
attachment being done with a worm-geared hose clamp. There were times when I was plagued
by RF feedback due to the many wires acting as resonant antennas at various operating
frequencies; I also had concerns about the needed low-resistance of a single wire grounding
system.
I spotted some steel plumbing strap in the hardware store one day, and pictured that as a much
better solution to my RF grounding woes...and it indeed worked out that way in my case. The
steel plumbing strap is inexpensive enough, between $1 to $2 for a 10 foot blister-packed roll. A
couple of rolls of the strapping, plus a dozen 6-32 machine screws, nuts and washers are all that
need be purchased to get you going. The particular strapping I'm using is 3/4" wide, by 10 feet
long and it contains alternating 1/4" and 9/64" holes throughout its entire length. It's made for
hanging plumbing pipes from wooden rafters, etc., and is easily cut with tin-shears or a hacksaw
to provide you with the exact length needed.
Figure 1 shows the strapping as it comes from its blister-pack. It's easily bent around a circular
fastening point or shaped any other way that might be needed to achieve the desired end.
Figure 2 shows the connection point to the cold water pipe in my own installation and Figure 3
illustrates how a solid splice is made to extend the strapping length. Figure 4 shows how I've
chosen to tap onto the main strap at piece each equipment, and Figure 5 depicts how that piece
of gear can be securely fastened to the tap-off using the existing grounding stud present on most
pieces of amateur gear now being sold.
Since installing the strap grounding system, I've experienced no further in-shack RF feedback
problems. What's more, the jumble of grounding wires has disappeared and I've no further
doubts about the adequacy of my shack ground system. Be sure that you ground every piece of
gear, including any coaxial switches, antenna tuner and the chassis of your shack computer.
The more thorough you are in this area, the fewer problems you'll experience with stray RF
and/or digital noise ending up where it shouldn't be".
James E. Brown, AE4EY
134 W. Dilcrest
Florence, KY 41042
Moderator's note: Jim's idea is a good one to keep in mind for your next shack re-building
project. Since it's relatively inexpensive steel strapping, there will be some inherent RF
resistance present in it, but it's shear bulk helps to minimize that factor. If you can find copper
hanger strapping, so much the better, but be careful not to mix dissimilar metals if you can
possibly avoid it (because of the possibility of electrolytic action taking place at the junction). Also
be sure to carefully sandpaper or wire brush all connecting points for the lowest resistance
connections. Both steel and copper quickly oxidize to form high resistance surfaces. If you're
using a cold water pipe as the final ground reference, make sure that that connection is also well
cleaned, and that there are no non-conductive pipes in the line all the way to where it enters the
earth ground. Any water meters or other in-line devices should be by-passed with a heavy wire
shunt, since their carry-thru conductivity may be questionable. In a basement installation, quite
often a hole drilled through the concrete floor, and a 6 or 8 foot ground rod passing through it, will
end up being the shortest and best path to earth ground. Be careful not to inadvertently hit any
under-floor pipes or tiles!
A LINE OF AFFORDABLE PROJECT BOXES
If you're anything like me, you can never have enough sources for small project boxes, perhaps for a microphone adapter, a couple of outboard switches or maybe a small-circuit idea consisting of just three or four parts.
One such source of small boxes that I recently came across is Sescom, Inc. of Henderson, Nevada. Their mainstream business is in serving the independent television production community with cables, adapters, amplifier modules, etc., but their newest catalog also boasts a number of what they call "Mini Project Boxes" that are also perfect for many ham radio construction needs. Their MPB-1 at $1.95, for instance, is only 1"x2"x1", and has proven to be very useful in my own ham shack for small projects. Their current full-line consists of a total of 24 varied sized project boxes, from the MPB-1 mentioned, the MPB-2 measuring 1"x4"x1", MPB-3 at 1"x6"x1" and on up to the MPB-24 at 4"x14"x3" at $6.10.
The boxes are an exclusive design and consist of four flat aluminum sides, two flat aluminum end pieces, four channeled-aluminum 90o "micro extruded" corner angles and eight self-tapping steel end-screws. The flat aluminum sections are .04" thick and are unpainted; they're easily drilled or punched medium-hardness aluminum stock, with plastic protective film on both sides for scratch protection during shipping and handling. They arrive unassembled, an interesting concept in mini-box shipping and storage, that also makes drilling or punching much easier since you're always working on a flat piece of stock.
Assembly takes only a few minutes, and consists of slipping the flat aluminum side plates into the channeled corner angles (see Figure 6), then attaching the two flat end plates with the eight small self-tapping screws. The box can be primed and painted if desired - either assembled or unassembled - to match whatever piece of existing equipment that the user might want to complement, or it can simply be left natural, perhaps giving it a brushed finish with a piece of soft steel wool.
Another interesting side benefit of the assemble-the-box-yourself design is nearly unlimited customization of the final size. If you need a box that fits exactly into a given space, one of the Sescom "Mini-Project Boxes" may be just the answer. Simply choose the box closest in size - but slightly larger - than what you would ideally want, then cut the stock down to the exact size needed with a bandsaw, and you'll have the perfect box to fit your available space. This is something that's virtually impossible to do with pre-formed or molded project boxes.
Sescom's phone number is 1-800-634-3457 - or you can write to them at 2100 Ward Drive, Henderson, NV 89015-4249 - and request their latest catalog. Also unique is their free UPS ground shipping on all orders over $20 - plus a 10% discount on quantities of ten or more of the same size box. Not a bad deal.
By the way, any commercial products that I mention in this column are completely unsolicited; they're either items that I've actually tried, or ones that have been recommended by 73 readers. I've not been approached by any manufacturer and wouldn't respond if I were. The intent of this column is to inform 73 readers of ideas, tips, suggestions and, yes, sometimes unsolicited products if they apply. It's not a paid ad sheet...just wanted to make sure that was said.
DE Dave, NZ9E
A handy paddle reversing switch
An idea submitted by Gary Bartlett, VE1RBG of Nova Scotia fits well into the Sescom MPB-1 project box talked about above. "As an ardent CW Op, I frequently carry my own paddles with me when operating another's station - such as when I'm on Field Day. Not every rig, however, is polarized the same way, with regard to which input connection is "dit" and which is "dah". Trying to re-wire the paddles each time, on a cold and dark night - isn't really the answer. The real answer is a small, sturdy project box, containing an easily operated DPDT paddle-polarity reversing switch...one that will work from one set of paddles to another, as well as from one transceiver to another. The circuit shown in Figure 7 is that answer. Fitted into a small aluminum box, the reversing switch will also allow you to change "keying hands" quickly, such as when the need to log with your right hand forces you to send with your left. Few Op's can master that feat, but the reversing switch makes it possible."
Gary Bartlett, VE1RGB
24 Lawrence Place
Wellington
Nova Scotia B2T 1A3
Canada
"Quick testing" capacitors with an ohmmeter
Peter Albright, AA2AD of Lakewood, New York, has set down some good information for us on the theory and practice of testing capacitors with the absolute minimum of test equipment.
"Did you know that your analog (needle style) multimeter can be used in the "ohms" position to
test capacitors? Although the theory is straightforward, practice is a bit tricky because of
differences between real-life multimeters. Follow along an you'll see why.
THE THEORY: In a dc circuit, capacitors act like a reservoir, but holding electrons rather than
water. When a D.C. voltage is applied to a capacitor, it fills (charges) as electrons pile up on the
plates. While it's charging, there is measurable current flow in the leads. Current flow, or
amperage, is greatest when the capacitor just begins to charge; at the instant that voltage is first
applied, the capacitor looks pretty much like a short circuit, with a resistance value of near zero
ohms. Current flow approaches zero as the capacitor approaches a fully charged state. When
fully charged, the capacitor looks like an open circuit, with nearly infinitely high resistance. A
perfect capacitor would hold this charge forever, or until the electrons are drained off by some
external circuit connecting the capacitor's two plates. Even a real-life capacitor can hold its
charge for quite some time.
An ohmmeter works by applying voltage across the device to be measured. Although the meter
is calibrated in ohms, it is actually measuring current flow. Remember Ohm's Law: I=E/R. For a
given voltage, the lower the resistance, the higher the current. An interesting, counter-intuitive
corollary is that analog ohmmeters put a resistor network between the meter and the device to be
tested. When you switch the meter to a higher resistance measurement range, the resistance
value of that network is increased.
There's one final piece to the puzzle. When a capacitor is charged through a resistor, an
elementary timing circuit is created. Increasing either the value of the resistance in ohms
(limiting current flow) or the value of the capacitor in farads (the size of the "reservoir"), will
increase the amount of time that it takes for the capacitor to fully charge, and for that charging
current, measured in amps, to drop to zero.
THE PRACTICE: As always, begin with a careful visual inspection. Defective capacitors often
are physically deformed by bulging, leaking or showing heat damage. They may be
"microphonic", showing functional instability when tapped gently with a plastic stick while the
circuit is active. A microphonic capacitor is bad, and no further testing is indicated. After you
have decided that there might be a defective capacitor in the circuit, follow these steps:
1.) Turn the rig off and unplug it, or remove the battery if that's the source of power.
2.) Make sure that the capacitor is fully discharged by placing a direct short between its two
leads or terminals with a clip lead. Remember to be careful: if the capacitor is a large
value power supply electrolytic cap, it can deliver enough current to put a nice nick in
your screwdriver blade, even at 12 volts! It's always a good idea to discharge large
capacitors (or capacitors in high-voltage circuits), through a 100 ohm, 2 watt resistor,
for a full minute or more before putting a dead short across its leads.
This last step was important - it protects you, your equipment, your tools and even the
component to be tested.
3.) The capacitor to be tested must normally be removed from the circuit. It's sufficient to
disconnect only one lead, leaving the other lead soldered in place since it's only a two-
terminal device. After you disconnect the capacitor, discharge it again to be sure its
"reservoir" is completely "empty". Even with a dead short across it, a capacitor may
take several seconds to completely discharge, because of its inherent internal resist-
ance. Good tehcnicians always practice accepted safety techniques!
4.) Now set your analog multimeter to measure resistance. The range setting that you'll
choose, will depend somewhat upon both the value of the capacitor to be tested, and
upon the characteristics of your particular meter. On my favorite meter, I generally
use the R times 1 range for electrolytic capacitors larger than 50 mfd, and the higher
scales for those smaller capacitors - up to the maximum of the meter's range for very
small ones of .001 mfd or less.
Remember the theory above? By changing the meter's range setting, you're putting
different resistances in series with the capacitor, thus making the time constant of this
series charging circuit long enough, so that you'll be able to see the meter move as the
capacitor takes on a charge.
5.) Next connect one ohmmeter lead to one of the capacitor's leads. For electrolytic
capacitors, but be sure to observe polarity of the capacitor as marked on the case.
You can't assume that the negative lead of your ohmmeter applies negative voltage to
the outside-world, so check your ohmmeter's polarity with a second voltmeter.
6.) Watch your meter's needle and touch the free meter probe to the other capacitor lead.
The needle should quickly swing toward zero ohms, and then reverse direction and
then more slowly work its way back toward infinity. The speed at which this happens
depends on the value of the capacitor and the characteristics and range setting of the
multimeter. If all of this happens too fast to see, return to Step 3 (discharge the
capacitor), and try a higher range setting on your multimeter. If, on the other hand, the
meter's needle moves excruciatingly slow, you can simply switch the meter to a lower
range setting without harming anything.
7.) If the meter never swings toward zero ohms, the capacitor is open, and defective. If the
meter never returns to infinite resistance, the capacitor is "leaky".
8.) When the meter reaches infinite resistance, remove one lead. Wait about twenty
seconds, then reconnect the lead. The meter may twitch a bit, but if it noticeably swings
back toward a low resistance reading, the capacitor is leaky. A good capacitor holds a
reasonable charge for longer than twenty seconds.
You can practice this technique on a variety of capacitor values, to get a feel for what should
happen with the different sizes and to determine which range on your own mulitmeter gives you
the most satisfactory reading times. You should get no false negatives: if the capacitor is leaky
or open, it's bad. A good reading is not absolutely conclusive, however, because the capacitor
may break down under the higher voltage of the actual circuit it's being used in, or it may have
changed in value. This "quick test" tells you nothing about the capacitors voltage break-down
point, nor does it give more than a rough idea of the actual value - other than by the time it takes
to charge through a certain series resistance.
Also, keep in mind that when replacing a capacitor in any tuned circuit, it is important to use an
exact replacement, both in terms of value and type (the material that the capacitor is made of can
be critical). The higher the frequency at which the circuit operates, the more critical that
replacement exactness becomes. The replacement capacitor's lead-lengths should also match
the original and its physical placement should replicate the original as closely as possible.
In the case of power supplies, you have some more leeway; except for the voltage rating, which
should be the same or slightly higher, the capacitor's value can generally be up to 150% higher
than the original.
Finally, never use a capacitor with a lower voltage rating than the original, and always strictly
observe the polarity markings on electrolytics and tantalums. If you ignore this caution, you'll
eventually have a capacitor explode inside your rig like a small firecracker, leaving you with an
unpleasant cleanup job."
Peter Albright, AA2AD
23 E. Summit Street
Lakewood, NY 14750
Hot tips!
Here's a tip on how to spot broken solder connections in ham radio equipment from Michael Fratus, of Richmond, Texas. "Solder breaks make up a higher percentage of direct and indirect causes of failure in electronic equipment than many people might off-hand think. When working on any ailing printed circuit board, if you notice a semi-circular ring around a solder joint - or any sign whatsoever of crystalization or fatigue - touch up the connection with an appropriately hot soldering iron and a bit of fresh 60-40 solder. Look especially at the connections on heavier components, any PC board connectors and all board-mounted controls for signs of "flex" stressing. This can be a particular problem in a mobile environment where lots of vibration is present, and also where extremes in temperature are most likely to occur.
Any 'stress fractured' solder joint can become thermally unstable - resulting in an intermittent connection with hot and cold - and is often responsible for what might seem bizarre symptoms. Unless you solve the "real" cause, you'll be working on that piece again! Taking the time to quality-check the unit while you have the board exposed, will give you more time operating and less servicing it in the futrure!"
Michael Fratus
Dept. of Criminal Justice
Inmate #650394
Jester - 3
Richmond, TX 77469
And finally, Bill Thim, N1QVQ took up my challenge and wrote in with this hinge-and-lock arrangement suggestion for KB0SJX, Paul Veal's easy-up, easy-down vertical antenna suggestion in the February 1996 Ham To Ham column. Bill wrote: "I liked KB0SJX's quick set-up for his HF vertical antenna in the February 96 column. Here's an extension of that idea that includes two husky pivot plates, and two secure locking pins, that might make the "raising party" even quicker - and easier on the back!
Two appropriately sized heavy-wall plates can be securely (and permanently) attached on either side of the ground masting and then a pivot point created using a 1/2" bolt (with double nuts on the threaded ends) and passing through both plates and the ground masting itself (see Figure 8). The installation is completed by inserting two heavy "quick-release" locking pins through two clearance holes, one in the two plates alone, the other in the two plates and passing through the base of the antenna masting (also illustrated in Figure 8).
Make sure that you use hardware that's appropriate for the loads to be expected, since it will be taking the brunt of any stresses casued by wind and weather while the antenna is in the upright position. Non-rusting hardware, if available, is always the best choice. The small notches at the top of the fixed plates is for a third "temporary" locking pin; this one is simply dropped into place to temporarily hold the antenna upright while the other two locking pins are inserted. The back-brace keeps the antenna from falling in a backward direction during this process. Once the pins are all in place, they will become the major "locks". Remember that all holes drilled into any tubing will weaken the tubing to some degree at the point of drilling, so keep them far enough apart and never more than one set at any point along the tubing's length.
Additionally, if you would like to run the coax underground back to your shack, as Paul did, consider using PVC piping as a raceway. It helps to protect the coax and also makes running any other cables in the future, an easy job. You can buy PVC pipe with holes already drilled into one plane of it, in 4" and greater diameters. 4 inches may sound like a lot, but it can fill up fast if your station antenna farm begins to grow...who's doesn't? The bigger you can manage, the better. Of course you can also drill holes along a length of smaller PVC pipe if your future plans are more modest. The proper way to lay the pipe underground is shown in Figures 9 and 10. A moderately sized trench will be needed, preferably below the frost line. When the pipe is laid, the holes should be straight down, the pipe should rest on blocks or loose gravel for drainage - cinder blocks with the hollow channels pointing up & down are an excellent choice. The entire length of pipe should then be "draped" with plastic sheeting over the top, to act as a water-diverting shield when the soil is placed back over the top of the trench. Sounds like a good bit of work - and I suppose it is - but doing it correctly will save you countless problems in the future.
On the far end of the pipe, exiting of the cables can be done with a PVC mating-cover with holes drilled into it and then grommeted, to pass the cables needed, as shown in Figure 11. Final sealing might be done with flexible silicon sealant, so that the cover can be removed later on for a new run. Another way to handle the out-of-doors end of the run is to construct a "weather elbow" out of PVC fittings as in Figure 12. This type of scheme will not allow water to enter the pipe's end, yet provides easy access for new cable runs in the future - though more 90o turns are involved. A wad of fiberglass insulation pushed into the end of the pipe will discourage its habitation by insects and other "unwelcomed" visitors!
The shack end of the pipe ideally should go through the wall of the building itself, for maximum convenience and weather-resistance. You might even put a small "hamfest-gem" 3 or 4 inch whisper fan at the building end, pulling air from the pipe into your shack, for free cooling in the summer and warming in the winter! The fan will also help to replace the air inside the pipe and keep it dryer.
Finally, an electrician's "fish tape" should be used for the initial cable pull...don't forget to put in some sort of "come-along" rope that can be used for future pulls. It can be simply a loose rope running along side of the cables, or a "trolley" arrangement can be configured with a "loop" of rope - separately hung - that runs the entire length of the piping. Sometimes, a loose "come- along" rope, though simple to install, will wind around the cabling, making it more frustrating to pull in future runs. Consider using the "trolley" idea if you can; Figure 13 shows one way that this can be accomplished on a fairly straight run. Its practicality depends to some degree on the length of the run and on the size (diameter) of the pipe laid as well. Choose whichever method you feel is most practical for your own installation."
William Thim, Jr., N1QVQ
50 Miller Road
Broadbrook, CT 06016
Moderator's note: It's obvious that Bill has thought out the problem well, and his suggestions might apply to all of us, no matter what antenna system we might have in mind. As Bill pointed out, it's vitally important to keep an underground conduit raceway dry. Coax cable was never meant to "tread-water". Make sure that the cable you choose for an underground setting is free of any (even slight) defects in the outer jacketing. Any moisture whatsoever inside the shielding of the cable will literally destroy the RF shielding quality and conductivity of the cable's shield conductor. The braided shield must make good electrical contact with its neighboring wires to represent a continuous "pipe". We can get away with the flexibility of a braided shield in our cables - as opposed to a solid outer piping - only because each strand of the shield overlays every other strand, simulating a continuously-walled pipe; but that simulation must be maintained throughout the length of the run. Be sure to tune in next month for more worthwhile tips, ideas and suggestions.
DE Dave, NZ9E
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 all correspondence relating to this column to 73 Magazine's Ham To Ham column,
c/o Dave Miller, NZ9E, 7462 Lawler Avenue, Niles, IL 60714-3108, USA. All contributions used in
this column will be reimbursed by a contributor's fee of $10, which includes its exclusive use by 73
Magazine. We will attempt to respond to all legitimate contributor's ideas in a timely manner, but
be sure to send all specific questions on any particular tip to the originator of the idea, not to this
column's moderator nor to 73 Magazine.