Ham To Ham #38 - November 1998

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

Hi-Tech clean-up Here's a handy little gadget that I ran across recently at the hardware store. It's called a PrepPen (reg. trade mark) and is made by Pro Motor Car Products of Clearwater, Florida. The intention by the manufacturer is that the PrepPen be primarily used for fine detail standing, such as those hard-to-get-at contours in fancy millwork, or the small recesses in metal castings that are otherwise inaccessible to normal sand paper and other grit-based materials. In fact, Pro Motor Car Products bills its PrepPen as "The High-Tech Sanding Tool".

While cleaning wire ends prior to soldering is in fact mentioned on the package, I've found that the PrepPen can be used for all manner of electronic cleaning jobs around the shop. In addition to sprucing-up highly corroded wire ends, it's also handy for burnishing terminal connections, PC board solder pads, corroded portable-equipment battery contacts, soldering iron tips, and anything else that needs fine "touch-up" cleaning prior to use. While the PrepPen will remove some of the softer enamel-wire finishes, it won't work (by itself) on Formvar (reg. trade mark) and others that are extremely tough, they'll still need to scraped. It can, however, be used for the final, just-before-tinning cleanup however.

Physically, the PrepPen is about the diameter of a husky marking pen, which makes it easy to handle and control. It's plastic "pen" shaped body houses a bundle of 20,000 very fine strands of glass fibers (each finer than a human hair), attached to a screw-thread feeder cartridge. You can adjust the length of the fibers exposed from the working-end of the "pen" by simply turning the adjusting post at the far end. Figure 1A shows the overall concept of the PrepPen, and Figure 1B illustrates how the glass fiber replaceable cartridge (about an eighth of an inch in diameter) itself looks. Some of the other jobs that the manufacturer mentions (in addition to cleaning ends of electrical wires) are removing corrosion from plumbing parts, brushing rust from small paint-chipped-areas prior to touch-up (such as on an automobile), sanding hard-to-get-at recesses prior to painting, preparing parts for gluing (it dulls a shiny finish nicely) and cleaning battery contacts.

The PrepPen measures 4-3/4" long and is about 9/16" in diameter at its widest points. The glass fiber cartridge is 1-3/16" long, and of course wears-down as the tool is used, but it still should last a reasonable amount of time before the cartridge needs replacing. As mine was purchased, the manufacturer thoughtfully packaged one spare cartridge in the hollow of the rear-adjusting post (the unit easily comes apart for cartridge replacement). The PrepPen is available at most automotive, hardware, and home center stores nationwide. de NZ9E

Analyzing ... the problem! One of our regular contributors, Stephen Reynolds N0POU, wrote in with this caution ... "using an RF antenna analyzer to determnine the accuracy of the match for an HF antenna can sometimes be misleading ... especially if a strong local broadcast station is on the air in the area. Strong RF fields can throw the analyzer off because it can't distinguish between locally strong out-of-band signals, and the signal that the analyzer itself is developing." Interesting point. Stephen also mentioned that one must be very careful when connecting the coax connector onto the Autek RF Analyst (reg. trade mark). Any twisting of the connector's center pin, during installation or removal, can break connections on the insdie of the unit, necessitating time- comsuming (and perhaps costly) repairs. His answer to the problem was to permanently install a UHF right-angle adapter onto the Autek's UHF fitting, and only install the coax cable connector to that right-angle adapter, thus absolutely avoiding any twisting of the instrument's built-in coax fitiing during normal usage. Good tip Stephen.

Stay in control Jim Kocsis WA9PYH offers this tip on how to control just about anything that you'd like to turn on and off, from as many locations as you you can imagine: "If you need to control a circuit from several different locations, then this may be just the thing you've been looking for! Using two SPDT switches to control a circuit from two distinctive locations is no big secret ... so called 2- way circuit swithing has been used for years in the electrical trade and it's likely that you now have one or two lighting circuits in your home controlled by 2-way electrical switches.. Figure 2A shows how the circuit is wired, and of course it's used to turn the same lights on or off from two different places. But what if you want to have more than two different control locations?

Electrician's use 4-way switches (DPDT switches that are cross-wired internally so that only 4 of the 6 terminals are brought outside) to accomplish just that task. Figure 2B shows how it's done. SW1 and SW3 are SPDT 2-way switches and SW2 is a DPDT internally cross-wired 4-way switch. No matter what position any of the switches ends up being left in, at any of the locations, the circuit can be turned on or off from any other location.

Now take a look at Figure 2C. Here we see two SPDT 2-way switches and two DPDT cross- wired 4-way switches. This combination allows us to control our circuit from any of four distinct locations, again, regardless of what position any of the switches are left in at any of the other locations. In fact, just by adding more DPDT cross-wired 4-way switches, you can control the circuit from as many positions as you wish (just remember that you need to end up with the SPDT 2-way switches at each end of the circuit as shown.

In addition to using this scheme to control a lighting circuit, you can use it to turn on or off anything you'd like, such as a whole-house speaker audio feed from your ham shack! Just use miniature SPDT and DPDT toggle switches, capable of handling the voltage and current of the circuit that you wish to control, and wired as shown in Figure 2C. Of course if you're controlling a 120 volt AC circuit, use only UL approved 2-way and 4-way electrical power switches and wiring specifically manufactured for that purpose."

Pot luck! Here's some helpful input from Herb Foster AD4UA: "The MFJ-418 Pocket Morse Code Tutor is a really handy little device and truly does fit easily in just about any pocket. The earphone option is particularly nice, sparing innocent bystanders from the pain and misery of the Morse code discipline! Since I use my '418 daily to keep my CW speed up to par, it eventually developed a scratchy volume control, apparently just from plain wear. The obvious fix was to replace the control entirely; it's a 10 K pot with a switch, and is available from MFJ (601-323-5869 for credit card orders) for $3.48, including shipping.

Here are a few tips to make replacing the '418s volume control a bit easier: be sure to use care when opening the case, since there's a flat ribbon cable that connects the board to the LCD display. Try to disturb this cable as little as possible. The old pot comes out easily by using a pair of miniature side-cutters to cut the five connecting straps that connect the pot to the board. Then a fast touch with a fine tip iron will remove the stubs of these straps. Save the knob, as the replacement pot/switch doesn't come with one. After you've soldered the connecting straps to the new pot, just drop it in, solder down the five connections to the board, and install the old knob (it takes a micro-tipped Phillips screwdriver).

When the 9 volt battery gets weak, you'll notice the LCD display blinking in time with the transmitted code. This is a good indication that it's time for a new battery.

I feel that MFJ may have slipped on one small point in the design of the '418. If you like to be able to observe the LCD display as you use the Morse Tutor in your CW practice, the natural tendency is to lay it down on a desktop with the LCD display facing upward. Unfortunately, this also puts the speaker facing downward toward the desktop, and the sound becomes muffled. The fix to this is to buy a package of rubber bumper feet, available widely from hardware stores and super markets, and cut out small pieces about 3/8" square. Put these at the four corners (on the underside), where the speaker grill is located. Two of them will end up on the corners of the battery cover. Now you should be able to put your '418 on a desktop with the display upward, and hear the code audio loud and clear!

By the way, using the MFJ-418 in the practice QSO mode and after a few exchanges, the calling station will say that he must QRT for a variety of reasons, the most imaginative one being to change the baby! These are the 90's, aren't they?"

As always, our thanks go out to those who've contributed their ideas to this month's column, Including:

Murphy's Corollary: A "fail-safe" circuit will usually destroy the circuit it's protecting!

Stephen Reynolds N0POU 510 S. 130th. Street Omaha, NE 68154

Jim Kocsis WA9PYH 53180 Flicker Lane South Bend, IN 46637

Herbert L. Foster AD4UA 3020 Pennsylvania St. Melbourne, FL 32904-9063

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.