Ham To Ham #16 - January 1997

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

With the first issue of the new year comes a nice variety of Ham To Ham tips. Many thanks to those who've sent in their ideas over 1996, often several ideas, as well as the new names that we're seeing for the first time. I'm always looking for more tips, ideas, suggestions and short cuts to keep the column going and growing, so please don't hesitate. The address is at the top.

Adjustable antenna tip

From William Thim, Jr. N1QVQ of Broad Brook, CT comes another good tip...Bill has been very supportive, with a number of good tips in the past, and this one is no less timely: "I own a portable antenna that covers several VHF/UHF ham bands, but one that must be physically adjusted for each different band, when operation on that particular band is contemplated. After losing the adjustment instructions once, I decided not to let that happen again, so I obtained the tuning instructions from a friend, then transferred them to the antenna's base using a customizable rubber stamp kit like the ones sold in many office supply stores. A coat of clear lacquer spray over the stamping finished the job with permanency. To make sure that I always had a tape measure with the antenna for those critical adjustments, I made a trip to the XYL's favorite sewing supply store and purchased one of those 'cloth-tape yardsticks' , attached the 'yardstick' to the antenna using a 'twist-tie', and now I know I'll never forget to have everything needed for adjusting the antenna no matter where I might find myself at the time that it is needed. You can 'customize' this basic idea to fit your own antenna-element-needs, depending upon the particular model of adjustable antenna that you have."

Moderator's note: Good idea, Bill; also, don't forget to "twist-tie" that special allen wrench or an inexpensive small screwdriver to the package, if loosening and tightening set-screws is involved in the adjustment proceedure. A small, plastic "zip-lock" (reg trade mark) bag with a hole punched into one corner can hold these odds & ends. The bag itself can then be secured to the antenna package with a "twist-tie" or short length of cable-lacing twine.

Not written in stone

David Hyman KB0ONF of St. Paul, MN suggests a way that you might use to cut down on paper costs in your ham shack: "I've been able to drastically cut down on the amount of scratch paper that I use by assigning the note-taking-task to a scrap piece of 1/4" thick, 8 1/2" x 11" chunk of white plexiglas (reg trade mark) instead. Smooth white plexiglas is available from surplus outlets around the country at very reasonable prices...often sold by the pound (look in your yellow pages under 'surplus-retail'). The plexiglas can be easily cut with a bandsaw, or simply scored with a utility knife, then cracked over the sharp edge of a table...the ragged edge then either filed or lightly "fire polished" with a propane torch (go easy, it doesn't take much heat).

The white plexiglas is now the 'perfect' writing surface for either dry marker pens or the water soluable pens sold in art stores and office supply outlets. I prefer the 'dry markers' myself, one of which is the Expo Markaway 3 (reg trade mark) , No. 83000, by Sanford. Black is probably the best color and a chisel-shaped tip works nicely for me.

Cleaning the white plexiglas surface after use is easy too. A dry erase spray cleaner is sold specifically for this purpose, but I've found that lacquer thinner, poured into a defunct glass window cleaner spray bottle, works just as well and at a fraction of the cost. The lacquer thinner doesn't seem to attack or soften the white plexiglas that I'm using in any way."

Moderator's note: I've used a similar idea in my own ham shack using a "note jotter", consisting of a washable pen and plastic-coated tablet, made for wall hanging near a kitchen telephone. In this case, a damp cloth will "erase" everything so that I can start again with a "clean slate"! What were those little marker slates with a clear plastic on top, followed by a translucent sheet and ending with a black waxy surface below called? You simply lifted the two top sheets to erase the whole tablet...great fun to use as a kid I remember.

Considerable cable considerations

Here are a couple of good tips on coax cable from Phil Salas AD5X:

"I'd suggest that you consider using 9913 coax cable, instead of the more popular RG-213, for your VHF/UHF antenna feedlines. 9913 has about a third less loss than RG-213 at a given frequency, and is much easier to connectorize with the standard PL-259 UHF connectors. The inner insulation is easier to strip since it is mostly air! The shield is easier to solder to the PL-259 since the inner dielectric doesnít conduct the heat away as it does in the RG-213 type of cables. Cable X-perts (orders 1-800-828-3340, tech info 1-847-520-3003) sells 9913 for 42 cents per foot, which is only about six cents per foot more than RG-213. The disadvantages? You must take extra care to properly waterproof your outside connectors...since any internal water will flow easily through it's mostly air-filled innards...but you should carefully waterproof all outside connectors anyway...more on that next. Also, 9913 is not quite as flexible as RG-213, since the center conductor is a solid copper conductor. A stranded center conductor form of 9913 is available, but it's a bit more expensive...the choice is strictly up to you.

For waterproofing those outdoor connections and connectors, Iíve had very good luck with a product called 'Plast-Dip' (reg trade mark). It's a fast curing liquid plastic material that's intended primarily for coating tool handles. A can of the thick liquid costs about $7 at Home Depot (reg trade mark) and other hardware and home centers...but it should last you a good long while. I usually put two coats of it on all of my outdoor connections. For wire connections, such as separating a coax shield and center conductor for feeding a dipole antenna, I immobilize the point where the shield and center conductor separate using hot glue (hot glue guns are great for lots of things). Then I attach solder lugs to the ends of the shield and center conductor...where attachment to the antenna will take place. Finally I dip the entire end (including the solder lugs) into the Plast-Dip and let it cure. After curing, I'll use a sharp hobby knife to trim off the excess Plast-Dip insulation that covers the ends of the solder lugs. Neat, easy and very waterproof!"

Moderator's note: Good suggestions, Phil. Waterproofing outdoor coax fitting can't be over stressed...any moisture in even the solid insulation coax is disasterous. The shield of a coax must appear as a solid conductor to RF, that is, each overlapping strand of braid must touch as many of its neighboring strands as possible, seeming to be a solid outter pipe. Water of any sort inside the coax jacket spoils this shielding quality...and you can't tell it by DC resistance checks alone...it must be tested with true RF testing, looking for loss or leakage. Even a small knick in the out-of-door cable's jacket must be re-sealed. Phil's suggestions on the best (lowest loss) cable are also well taken...even if your entire cable run can't be of a low-loss variety, every foot that you can manage will be that much better.

Crystal DIP

J. Frank Brumbaugh, KB4ZGC/W4LJD, of Salinas, Puerto Rico has contributed another interesting idea this month: "When constructing crystal ladder IF filters, you can save PC board space, simplify the layout time and make the crystals much easier to check or replace by simply using a standard 16-pin DIP socket to hold the four crystals needed. Interestingly, the HC-18/U style of crystal with wire leads, will plug-in directly across 3 pins if a standard DIP IC socket, A quick look at Figure 1 will illustrate how a 4-crystal filter would be wired using this scheme. Just clip the HC-18/U's leads to about 1/4", and plug-in the crystals after all of the heat-producing soldering has been done. If you need more than 4 crystals, just add another DIP socket!"

Moderator's note: Clever idea, Frank. By the way, Frank's right, a wire-lead HC-18/U fits perfectly across 3 pins of a normal DIP socket. I'd recommend using the best DIP sockets you can afford for this application...the ones with round "machined" pins hold the crystal nice and tightly.

Viral protection

Each day, computers are becoming more and more an integral part of our ham radio stations. From Terry Huckleberry N5FYI come these tips on protecting your computer from a dreaded viral attack: "Most virus infections occur as a result of exchanging floppy disks. The best mainline protection against infection is therefore the pre-screening of ANY and ALL incoming floppies...even before reading the disk's directory! By merely typing 'dir' for an infected disk, you can spread the virus to your own hard drive!

Most viruses also lie dormant for a period of time, before self-activating and causing any critical damage to your system. During their 'dormant' stage, however, the virus can be 'reproducing', spreading itself into other areas of your system, virtually undetected. The sinister virus programmers aren't looking for 'instant destruction', but rather for the widespread latent destruction made possible by waiting patiently to attack. This is one of the features that makes the more sophisticated viruses so devastating. Early discovery and elimination ends the virus' life-cycle.

The solution? Virus scan EVERYTHING that you import into your computer before doing anything with that program. Scan all outside floppies before even reading their directories. A friend of mine recently downloaded a virus scanner and found that there was a virus in the zip file of the virus scanner itself! Scan each installation of every program or data file...in most cases, you can stop the viral spread beyond the initial file that contains the disease if you're consistent with this policy.

Any virus detected should be considered dangerous!

A further warning...even factory-sealed program disks can't be considered absolutely viral-free, and due to the way in which files are often packaged, a program loaded directly from a factory boxed disk can't usually be fully virus scanned until it's installed on your system. The best policy then is to re-scan for viruses after each installation (and before actually running the program) on any newly installed outside programs. This may seem extreme to some, but so is the damage that can occur from an infected outside disk...ultimately, of course, it's your choice."

Moderator's note: Terry brings up some important points. It's a shame that we even have to worry about things like this, but we've all heard the horror stories of the reality of intentional viruses. As programming techniques and packaging alternatives become more sophisticated, it may be less likely that viruses will be able to spread as readily as they do today, but until that time, it's best to stick with the safest approach. There are numerous virus scanning programs available today, and Terry mentioned that he's had good results with F-Prot and Thunderbyte virus scanners to name just two. Additionally, make sure that your anit-virus program is a recently updated version...as the anti-virus scanners become more adept at ferreting out the culprits, the virus programmers counter with sneakier viruses...reminiscent of the old nuclear "Cold War" days!

Dispelling the equalizing resistor myth

This month, Rich Measures, AG6K, of Somis, California, helps to straighten out some of the confusion surrounding the why's and why not's of using equaling resistors and capacitors across high voltage diodes . "In days of yore, when silicon diodes were first introduced to the consumer electronics market, the absolute 'need' for equalizing resistors and equalizing capacitors across the newly discovered critters was admitted by virtually everyone 'in the know'. Today, things are a lot different. Silicon rectifier manufacturing technology has come a long way, and inherent similarity from device to device is the norm, not the exception. So are equalizing resistors and equalizing capacitors across the current offering of silicon rectifiers really needed now?

No, in fact, they can actually cause problems of their own in the series high-voltage power supply circuits found in most amateur HF linear amplifiers. Here's why: the little 1/2 watt carbon composition resistors normally used in this service were never designed to handle more than about 350 volts maximum DC across their relatively small carbon elements; most high voltage diode stacks used in modern linears are expected to carry twice that voltage...or more...safely. So over time, internal stresses within these 350 volt resistors can eventually cause one or more to break down - usually by decreasing gradually in value - and then the domino effect takes over. In short, one or more resistors failing, putting that much more strain on the rest, and eventually causing catastrophic failure of otherwise perfectly good parts in a series circuit such as the one described.

Instead of using equalizing resistors and capacitors these days, just make sure that the total PIV of the entire silicon rectifier stack will handle the total peak voltage to be expected, with substantial safety margin to spare, and leave it at that.

One factor that should be recognized , however, is that all of the rectifiers in a series-connected

circuit should have similar junction capacitances - using the same type number rectifiers will normally assure this. If they're not equal, then the reverse-voltage across the lower capacitance rectifiers will tend to be excessive, because smaller capacitors charge faster than bigger capacitors. It's a good idea, therefore, if rectifier types must be mixed in a series circuit, to equalize with disc capacitors. If some 6 amp rectifiers are used as replacements in a circuit using 1 amp devices - assuming that's all that the repair-person has on hand - then a .01uF disc cap across each device may help...but only because of the wide variation between those 1 amp and 6 amp rectifier natural junction capacitances. Again, there's no need to add 'equalizing' caps and resistors in a series circuit having all the same part numbers...and it can even do harm.

Here's one thing of interest that I once ran into, though it's not by any means a common problem. I encountered a production run of silicon rectifiers that apparently had poor spot-welds inside the rectifier casing itself. Internal heating and cooling eventually caused these welds to break, completely opening the rectifier from current flow...not a healthy condition is a series HV circuit. If one of the capacitors in the circuit is not being charged by its respective rectifier, then reverse current can be forced though it, and the results are noisy and messy. If you ever run into just one open silicon rectifier in a series HV circuit, don't take chances. For the ten cent price of a rectifier today, replace all of them, just in case it was the product of a poor manufacturing run. The normal failure mode for these devices is a dead short, caused by too much foreward

or reverse current, not an open. Be forwarned...be suspecious."

Power supply tips

Here, Peter Albright, AA2AD, of Lakewood, New York, offers some tips and techniques on practical linear power supply troubleshooting. "Linear (not 'switching') power supplies, are sometimes the easiest of the many circuits to be found in ham transceivers to troubleshoot, and they're also often the most prone to failure due to the demands imposed upon them. Quite often, diagnosis of other circuit failures can be traced to incorrectly operating power supply circuitry, so this part of the chain should always be checked for proper operating parameters before going into the more complex circuitry...just in case.

Most power supplies can be thought of as containing five basic blocks: 1.) the input interface block (the input line cord, protection circuit, power transformer, etc.), 2.) the rectifier block (where AC is converted into pulsating DC), 3.) the filter block (where the pulsating DC is converted into smooth DC), 4.) the regulator block (where output voltage stability is determined) and 5.) the output interface block (where current limiting resistors and/or wires and PC board traces carry the supply voltage to other stages of the transceiver). By thinking of the power supply in terms of individual blocks, it's often easier to isolate problems in the power supply using the logical steps of elimination.

The first analysis of any suspected power supply problem can begin with the unit's cover in place. Is the line cord in good condition, is the fuse intact (if accessable from the outside), what (if anything) unusual was noticed at the moment of failure, was anything spilled on the unit or did a voltage surge or lightning strike occur when the device failed? Was there any smoke or perhaps unusual noise associated with the failure? All of these 'external' clues can help lead us to the eventual solution to the problem. Always look first for the obvious, it can save countless hours of needless troubleshooting time (an intermittent AC line cord or fuse holder, for instance).

Once the cover is actually removed, leave the equipment unplugged and begin your visual inspection. Do any parts appear to be overheated? The transformer should be carefully inspected for signs of excessive heat (and odor associated with hot varnish), resistors should not appear darkened or discolored, electrolytic capacitors should not be leaking or bulging and all wiring or printed circuit board traces should be free of signs of excessive heat or thermal stress. Do the solder connections look clean and bright and are component leads clipped off so that they won't short to adjacent solder pads? Checking the power supply circuitry visually can save a great deal of time and effort if done systematically and with care. Anything at all that 'appears' suspect, should be removed and checked (or substituted) before going on.

Now we're ready for the power-on test, but be very careful; most power supply circuits can have lethal voltages present when operating, at least in the area of the primary fuse and the AC line circuitry. Always know where these points are before putting your hand inside of the chassis and proceeding with any voltage tests.

Having a schematic diagram can be a big help at this point. Check the diagram and locate the output regulator or regulators, then measure their input and output voltages with respect to ground. If you don't find the expected voltages (which are generally indicated on the diagram), then the problem could be in either direction, ie., either the correct voltage isn't being applied to the regulator's input, or the regulator is bad or the output voltage is being dragged-down by a higher-than-usual current demand somewhere in the circuitry that's being fed by that regulator. If you can open a link to that subsequent circuitry (by removing one end of a resistor, a steering diode or simply removing a wire), then you can eliminate the circuitry being supplied power as the source of the problem.

If you don't have a schematic diagram or other technical information, all isn't lost; often you can assume that the normal voltage reading obtained with a voltmeter across each of the large electrolytic filter capacitors will be about 80% of the voltage marked on the capacitors. It's not exact, but often enough to determine proper operation at least. Many times, voltage regulator IC's will have their regulated output voltage coded into the part number, such as a 7805 is a 5 volt regulator and a 7812 is a 12 volt device. Again, by working back through the various blocks, you can often tell if a reading 'seems' normal or if it's 'out of the ballpark' altogether. Experience helps, but experience is only gained through actual troubleshooting practice. Chances are, you'll do better than you think you're able to do, just by using these logical steps and thinking of the circuits in terms of the five basic blocks mentioned earlier. Why not give it a try?"

Moderator's note: Pete does a good job, as in the past, of outlining some time-honored proceedures for power supply troubleshooting. Knowing the normal failure modes of components is also helpful when attacking power supply problems, here are a few:

Fuses always open (badly blackened fuses usually mean a high-current short).

Power diodes normally short (smaller signal diodes, LED's and small zeners usually open). Resistors normally open or change value with overheating.

Transformers can open or overlapping turns can short internally (some transformers have internal thermal protectors that can open). Dry capacitors (such as disk capacitors) normally short or become very low-value resistors. Electrolytic capacitors can leak, dry out and loose their capacity to store energy. They can also short, often with dramatic results. Voltage regulator IC's can open, short or change their output parameters (they can also oscillate at times).

Note that these are the normally "expected" failure modes of components in power supply service, others are also possible. I've seen power transformers go up in smoke, high voltage electrolytics explode, regulator IC's blow apart in tiny pieces, resistors sputter and smolder, plastic insulation on wires completely melt away and fuses weld themselves inside of their holders. Power supplies or their feed lines are generally where these sort of things happen, so any suspect power supply component should be replaced as a precaution.

Murphy's Corollary: When working out a problem on a specific piece of equipment, try

sleeping on it...it's sure to make an impression!

Many thanks to this month's contributors...without your continued input, I'd soon run out of ideas...please keep them coming.

William Thim, Jr. N1QVQ

50 Miller Road

Broad Brook, CT 06016-9676

David L. Hyman KB0ONF

1455 Edgcumbe Road

St. Paul, MN 55116

Phil Salas AD5X

1517 Creekside Drive

Richardson, TX 75081

J. Frank Brumbaugh, KB4ZGC/ W4LJD

c/o Defendini

P.O. Box 30

Salinas, PR 00751

Terry Huckleberry, N5FYI

2409 Osage Road

Gatesville, TX 76528-1846

Richard L. Measures, AG6K

6455 La Cumbre Road

Somis, CA 93066

Peter Albright, AA2AD

28 E. Summit Street

Lakewood, NY 14750

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 judgement 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.

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 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 envelope (SASE).