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).

Ham To Ham #21 - June 1997

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

e-mail: dmiller14@juno.com

As the summer hamfest season begins in earnest, here's a tip to keep in mind: computer power supplies, the switching supplies used to provide 5 and 12 volts DC for the motherboard inside of the average desktop computer, seem to abound at hamfests and computer swapmeets these days. The supplies are usually rated at anywhere from 150 to 300 watts output and will supply 5 volts DC at about 15 to 20 amps and 12 volts DC at 6 to 15 amps. Don't overlook their possibilities as a compact, light-weight alternative voltage source for your 12 volt DC ham gear. They'll quite likely supply the necessary current to power a VHF or UHF ham transceiver, medium power "brick" amplifier or several components needed to complete a packet node or PBBS station...often at next to give-away prices!

I recently came upon a couple of these supplies that had been used in older, bulkier IBM AT PC cases, the other parts of which had been transferred to newer, smaller profile cases. Although one has to be careful in using switching power supplies around radio equipment (they can generate quite a bit of RFI and desensitize a transceiver's front end), most of the better supplies are pretty well shielded and RFI-proofed. It helps if you eliminate all of the unused output leads (of which there are often many) by cutting them off, taping up the ends and turning them back inside of the case. Only those supplying 12 volts DC and ground are needed. Now the supply can be checked out with a hand-held transceiver (preferably on the same band as the equipment to be powered will be operating) by using the hand-held's rubber duck antenna as a probe. If there is still some noticeable RFI from the power supply, it's often possible to further reduce it to acceptable levels by using a shielded primary AC power cord, and by installing ferrite beads on the output DC leads, just before they exit the supply's case (or by passing the leads through a torroid core a couple of times on their way out). Sometimes, just keeping a bit of distance between the supply and the radio itself is all that's needed. If the radio is being fed from an external antenna via well-shielded coax, then the chances of successfully using a "recycled" computer switching supply are even better. The main point here is not to overlook the possibility of using these supplies as compact, light-weight bench and RF equipment alternative power sources "just" because they were made for computer service.

de Dave NZ9E

A bright spot at last!

From Sam Ulbing N4UAU: "After reading Frank Brumbaugh's article entitled 'A Low Current Light' (73 Amateur Radio Today for November 1996, pg. 19) here's an expansion (and perhaps a little different twist) that I've uncovered. For over a year now I've also been using an LED as the main element in a 'non-night-blinding-flashlight' for my sailboat. The particular LED I use is somewhat unusual, and if anyone else might be planning to build a low current, easily portable flashlight, I'd recommend something like this one.

The LED I'm using is a Toshiba TLOA190P(WX) (available from Hosfelt Electronics, 2700 Sunset Boulevard, Steubenville, OH 43952-1158, order line: 1-800-524-6464...as item 25-276), but what makes it unusual is that it's rated at 18,000 to 36,000 mcd. That's a lot of mcd's when you consider that the average LED is somewhere in the range of 10 mcd, and the so called "Super Ultra Bright" jobs are about 3,000 mcd. This baby is bright!

The color of the TLOA190P(WX) is described as orange in the catalog, but I'd call it red. While

Frank brought up the point that red attracts insects, Iíve found it to be an ideal color out on the

water, because it doesn't cause night-blindness as other colors might. This is a very real concern

to a night-sailor, and perhaps to others who are involved in pursuits where maximum retention of night-vision is an important factor to consider (campers, drivers, pilots, security and police officers, etc.).

I'm using the TLOA190P(WX) LED as a low power light source in several ways, I've outlined some examples below:

Example 1 - I have 2 AA alkalines, a small slide switch and 20 ohm resistor all taped together (I'm not what you might term a 'case-building-expert'). The switch and LED fit nicely along the side of a 2-cell AA battery pack, and the package is simply wrapped in electrical tape. It's a small enough, 2.75" by 1.75" by .75", and it's the flashlight of choice that I carry with me on my sailboat. I can illuminate up to the tip of my mast head, some 55 feet up from the deck, and check on the wind tell-tails with this little beauty...that takes a bright light! With a 20 ohm current limiting resistor, current drain is only about 30 mA from the 2,000+ mAH available from good quality alkaline AA batteries; that equates out to better than 65 hours of continuous use!

Example 2 - I've also built a small LED flashlight onto floating key-chain, using a single cell 3 volt lithium battery (CR-2032, Hosfelt item 39-1194) and a combination of a slide switch and a mercury switch as the activation devices. When I'm on the dock at night I'll turn on the slide switch, and if I accidentally drop the keys into the water, they'll float upside down and turn on the LED so that I can find quickly them. I used a 100 ohm resistor in this application in order to keep the current draw low, so that the single lithium battery would last longer.

Example 3 - I also use one of the TLOA190P(WX) LED's as my sailboat's compass light. The red

light is more than sufficient and, again, doesn't affect my night-vision. Red is typically the color

that all sailboats use for compass illumination, but the LED will last virtually forever. In this

application, I'm also using a dimmer circuit (shown in Figure 1) so that I can adjust the brightness

according to my needs. The LED doesn't effect the compass' accuracy, since the low current

drain results in a very small extraneous magnetic field.

Example 4 - I tried using several TLOA190P(WX) LED's for the purpose of chart table illumination as Frank suggested. I tied several together in series, with a single current limiting resistor, and powered the series string from the ship's 12 volt battery. But these LED's are so spot-focused, that it really didn't work well enough for me in this application. All I really achieved were several bright red spots, fairly close together. Perhaps a less bright, less spot-focused LED would work better (as Frank recommended in his article), or perhaps a defocusing (diffusion) lens arrangement would help. I didn't feel that it was worth the effort in my own case to experiment any further at the time.

Example 5 - I use the LED as a general night light on the boat...actually I leave it on all the time. With a 2.2 k resistor in series with the Toshiba TLOA190P(WX) and powered by the 12 volt ship's battery, current draw is a minuscule 5 milliamps and it projects a nicely focused light on the companionway steps leading below decks.

Example 6 - I've found that it's even useful for holiday decorations. As just one example, I put two of these Toshiba LED's into a carved Halloween pumpkin, along with a little solid-state flasher circuit, to achieve a pair of 'winking goblin eyes', much to the delight of all of the neighborhood kids! Figure 2 shows the basic NE-555 flasher circuit that I used. There must some application hidden in here for Christmas as well!

No doubt there are many other uses for the Toshiba TLOA190P(WX) LED that I haven't touched

on, let's see some more suggestions here in the Ham To Ham column...we don't always have to talk simply radio! By the way, this LED is priced rather steeply at $3.50, but I feel that it has so many uses that it is worth every penny of it. LED's have such long life expectancies, that pro-rated over time, the cost is actually quite minimal. Like all solid-state lamps however, be sure that you limit the current to a safe value with an appropriate series limiting resistor. This particular LED can handle 60 milliamps, far more than most, but a 12 volt battery could destroy it instantly without the correct series limiting resistor. As mentioned before, this particular LED is bright enough, and focused enough, so that you can actually see it on a wall 10 to 15 feet away...even during the daytime. It might even be used as an inexpensive 'laser pointer' for low budget business presentations. And as with a laser, be very careful not to shine this LED into a person's (or pet's) eyes. It is quite intense and might very well result in unwanted damage. As with everything else, using common sense and obvious safety precautions, this LED has some interesting potential applications."

Moderators note: Sam is a noted author of technical articles who also enjoys the art of sailing in his free time. Our thanks go out to Sam for sharing these ideas with us and for a different look at the current possibilities with solid-state lighting. I've a feeling that it will be interesting to see what the future holds in this area of electronics.

Beaming with pride

From Tom Hart AD1B: "A number of years ago, I bought a 3-element 'Hilltopper' (reg. trade name) beam for 6-meters. In fact, it was back in about 1968 and I suppose you could say I've been somewhat remiss in getting it up and on the air! But after all, this is 'just a hobby' and there's no big rush!

At any rate, after purchasing the new MFJ 6-meter SSB rig, I decided it was now time to install my 3-element beam...still in it's original box! A necessary adjunct to any antenna package includes a system for supporting it, as well as a rotation method and all of the necessary cabling. Taking another look around at my yard and garage, I didn't see a good place to install everything in terms of 'quickly and easily'...two of my important priorities in this project. My thoughts then turned toward the possibility of a third-floor attic installation. I considered the less-than-optimum height factor and the inside-the-roof losses, but decided to give it try anyway. After all. 'it is just a hobby', HI.

Fortunately, my attic has ample room, so I set about designing the simple-to-build support structure (shown in Figure 3). It had to be small enough to make it through the trap-door access to the attic, yet large enough to support the beam and rotor as well as span the spacing between the attic rafters on which it sits. The bottom housing of the rotor, though not shown in the drawing, rests on the cross-2x4, maintaining the lowest possible profile and also adding to the stability of the installation. The beam, then, is mounted on another 1-1/4" dowel rod clamped to the top half of the rotor's housing, completing the mechanical installation. The two 2x4's that span the rafters can be glued, tied or perhaps screwed in place, to prevent any shifting of the mount during operation, if the sheer weight of the support system doesn't seem to be enough in terms of holding-power in your particular case...it's an individual judgment call.

I've been very happy with the results, it was easy to build and install, and it's served my purposes nicely. Wind and weather are obviously not considerations, and the beam should easily last another 30 years! Though not intended as a big 'DX grabber', my own primary interests on 6-meters are local contacts and checking into a few area nets. The indoor location has done that for me nobly. In fact, I'm now looking forward to building a 2-meter quad to go above the 6-meter beam!"

Moderator's note: Wow, Tom's attic must be a lot taller than mine, but his suggestions are well taken. Keep this easy support structure in mind if you think you can use an attic installation, perhaps to comply with no-outdoor-antenna covenants, or just to keep a lower profile in your overall 'antenna' farm needs. Tom's support could even be taken up to the attic in pieces, and the final assembly quickly completed via pre-drilled holes for long wood screws, or it might simply be glued together in-place (using either hot-melt or quick-setting liquid adhesives). Before installing any antenna in your attic, however, make a quick RF check at or near the frequency that you're interested in using. Some asphalt shingles have aluminum strips on their underside...used to keep the 'seal-tab' from sealing to the next shingle before installation. These 'unseen' metal strips can reek havoc on the passage of RF energy through a roof covered with this type of shingle...I know first hand...mine has them! After my new roof was installed a number of years ago, my off-the-air television reception was almost non-existent from my attic-installed TV antenna. The next time my home needs re-roofing, those shingles are going! A small battery operated TV set or ham hand-held transceiver operated from up in the attic should tell you immediately if your shingles are the of the "RF attenuating" variety or not. A pocket TV set tuned to Channel 2 to 6 will indicate how well 6-meters might work, Channels 7 to 13 give you a good idea about losses near our 2-meter and 220 Mhz bands. The UHF TV channels can be used to judge the results you might expect on 70cm and above.

Don't by-pass this!

From Ken Guge K9KPM: "You've probably seen them at hamfests, but perhaps you've simply

walked by...I'm referring to those B&W by-pass coax switches. Barker & Williamson makes a

coax switch that can be used for by-passing a linear amplifier, receiver preamp or other coax fed

accessory...just in case you might want to switch the device out of the circuit at times, with just a

flick of the wrist. Sure, you're linear amp already has a built-in by-pass relay, and maybe you're

transciever's RF preamp does too, but wait, that's not all that these handy by-pass switches can

do.

If you'd like to be able to route your transceiver's signal around everything, all at once, the by-

pass switch can do it for you easily. Most of us have the output of our transceivers feed into an

SWR metering circuit of some sort, maybe an external RF signal preamp, perhaps a linear

amplifier, a monitor scope, an antenna tuner (variable antenna matching network), a low-pass

filter, and often other necessary 'accessories'...all of which can cause problems of their own.

Loose PL-259 coax fittings, bad cables, intermittent internal connections can all interrupt our

QSO's even when the transceiver itself my be operating perfectly. A coaxial by-pass switch in

line is the answer and Figure 5 shows the idea in block diagram style. Just throw the switch into

its by-pass position and you can instantly 'work around' any and all of these potential QSO

spoilers! You can always troubleshoot the defective device later on, the main objective here is to

keep you on the air now.

A coaxial by-pass switch can also be used to effectively ground your antenna's transmission line,

and your transciever's input, when the station is shut down for the night. Figure 6 shows one

such arrangement. Of course youíll want to be sure to remember to place the switch in the ON-

AIR position whenever you're going to operate, but its QRT position will help to protect your

equipment from lighting or static induced damage when it's not in use.

On the test bench, a coaxial by-pass switch can come in very handy for checking the results of a

unit-under-test, by permitting you to quickly switch the unit in and out of the circuit (such as an

RF preamp), in order to make more accurate 'judgmental' decisions on whether the unit is really

doing what it's supposed to do.

I would guess that all of the previously mentioned uses are more or less what the switch

manufacturer had in mind when the decision was made to offer a product like this to the amateur

radio market...but there's one more! I doubt that B&W really intended for their 551A coax by-

pass switch to perform as a 2-position coaxial selector switch, but it can. If you look at how the

switch is internally constructed in Figures 4A and 4B, you can see that it's basically a SPDT switch ganged with a SPST 'secondary' switch. Ignoring the SPST 'secondary' section and connector #1, you can utilize the SPDT section as a standard 2-positon coax switch (an A-B switch). For instance, connecting a coax cable between connector #3 and your transceiver's output, you can switch between two separate antennas connected to connectors #2 and #4. You can also use the same idea in reverse to select between two transceivers and one antenna by connecting the antenna to #3 and the transceivers to connectors #2 and #4 respectively.

I'm using a variation on that idea in my own station as shown in Figure 7. In the cold weather, I prefer to do my HF and VHF operating from my upstairs office/den, rather than from the chillier basement ham shack. With a SPDT coax switch on each end of the line, I can use a single coax cable running up to the den by using the Figure 7 hookup. There are many other uses, limited only by your imagination and your own particular switching needs. I hope these suggestions have provided some food for thought for fellow Ham To Ham readers...and remember...don't pass-up this little gem at your next hamfest, itís not just for by-passing anymore!"

Moderator's note: Ken always seems to bring out innovative and surprising uses for devices that

many of us would never have thought of on my own...thanks for another Ken. By the way, the

manually activated by-pass switches that Ken referred to come in voltage-actuated coax relay

form as well. I've been using a 120 volt AC actuated coax by-pass relay in my own station to

switch my conglomeration of in-line accessories out of the circuit between my transceiver and my

antenna in an emergency...and it works nicely (I've had to use it a few times too!). Again, you

can often find these by-pass relays at hamfests with 6 volt, 12 volt, 24 volt and 120 volt coils

(both in AC & DC varieties). Just be careful that you know what voltage you're buying and that the coil reads continuity with an ohmmeter (you do carry a pocket-sized VOM with you to the

hamfests donít you?).

Murphy's Corollary: Any electronic component, selected at random, from a group of components having 99% reliability, will fall into that 1% remaining category!

Remember to keep your ideas coming this way, I'm always looking for worthwhile tips, ideas, suggestions, shortcuts and innovative ways of doing things in and around the ham shack...like those contained in this month's offerings. So again, as always, many thanks to the contributors to this month's column, including:

Sam Ulbing N4UAU

5200 NW 43rd Street

Suite 102-177

Gainesville, FL 32606

Tom Hart AD1B

54 Hermaine Avenue

Dedham, MA 02026

Ken Guge K9KPM

1107 E. Woodrow Avenue

Lombard, IL 60148

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.