Ham To Ham #19 - April 1997

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

It's the April issue, but no foolin', just some more good, down-to-earth tips and ideas to make our hobby more enjoyable and perhaps a little smoother running. Speaking of running, I'm running a little low on ideas, so please don't put off sending your favorites. Just jot down some thing (or things) that have made ham radio problem solving easier for you or for one of your friends, and send it to me at the address above. Uncle Wayne's elves will send you a check for $10 so that you can afford to buy a couple of the books on his "must read" list. He's recommended some very interesting ones...and here's some other interesting tips:

Superman's AA cells

Looking for a super-capacity AA cell? If you use rechargeable AA cells in any of your portable gear as I do, it might be worthwhile checking out the relatively new line of NIMH (nickel metal hydride) rechargeable cells. The NIMH chemistry automatically increases the mAH (milliampere-hour) capacity of a rechargeable cell by roughly 25%, and the new AA size NIMH cells boast an 1,100 mAH capacity (250mAH increase over even their newer 850mAH NiCad counterparts). NIMH cells can be charged in the same manner as NiCad's, using a one-tenth-capacity constant-current charger (110mA constant-current for the 1,100mAH NIMH cells mentioned). The NIMH chemistry has less tendency toward "memory effect" than does the NiCad formula and the cells can withstand more heat...all-in-all, a worthy competitor to the venerable mainstay of our rechargeable repertoire of cell chemistries. One source of rechargeable NIMH "AA" cells is DC Ace Electronics (847-821-8122) who lists the 850mAH "AA" Nicad's at $2 each and the 1,100mAH "AA" NIMH's at $2.50. When you compare these prices against the name-brand "use-em-once-&-toss-em-away" alkaline cells, the choice is pretty clear...especially for battery operated equipment that's used a lot. Though the better alkaline "AA" cells are rated at 2,450mAH capacity, 2 or 3 uses from the NIMH cells will quickly will put you in the "money-ahead bracket". Figure 1 shows the basic constant-current NIMH 110mH "safe" charger that I've been using for the "AA" cells in my GPS receiver.

de Dave NZ9E

CBer's PL

Here's an interesting tale of ground loops from Gary Holoubek WB6GCT of Fullerton, CA 92635: "Ever heard of 'CBer's PL'? That's the name I've given to the alternator whine that can be heard on all too many of even the best of ham radio mobile installations, and nearly all CB mobile signals! I thought I knew all about such problems until I installed a bank of radios into a friend's 1990 Lumina. My friend and I both enjoy having 3-band capability (146, 220, 440 mHZ) in our mobiles, and it took me several days to design and build the hardware to stack the equipment between the vehicle's floor and dashboard in a neat vertical rack array. Today's small cars can often be a real challenge! Everything worked fine...that is, until I did some customization...that's when Murphy struck!

Knowing that microphones sometimes never make it back to their correct hangers, and with use, could become a confusing tangle of microphones and coil-cables, I decided to use only one microphone for all three radios and switch it to the desired transceiver with a rotary selector switch mounted in a mini-box. The three transceivers are all Yeasu and so they fortunately use the same type of microphone and pin-out connections. Sounds simple enough!

The microphones are of the 8-wire type with signals for microphone audio, up/down frequency control, speaker audio, +5 volts for powering the touch tone circuit in the microphone, and of course a common ground for everything. With a little bit of imagination, I thought of all the different things I could possibly do to make this a really whiz-bang installation. Realizing that the radios would be used at night and the position of the transmitter selector switch knob would not be easily visible, I decided to use the +5 volts in the mic cable to power three LEDís...which would indicate which transmitter the microphone was delegated to. I even used a different colored LED on the switch box for each of the three transmitters. This would allow the operator/driver to determine which transmitter was 'ready-to-go' at a glance. It worked great! Even the speaker outputs from each radio were run through the switching box and an output jack made available to drive either an external speaker or a headphone for 'silent running'...all automatically switched with the micophone. Hey, no telling what an engineer can do with a little time and imagination!

When all was said and done, I ran into an interesting problem, something I'd not anticipated. At times, when switching the microphone via the switch-box, the transceivers would key into transmit briefly. I theorized that the problem stemmed from the fact that the touch tone (reg. trade mark) keying circuit in the mic - which was powered by the transceiver's +5 volts - would create a spike on the +5 volt line as the switch was rotated and the power to the mic's TT circuit was pulsed on and off (I was using a break-before-make rotary switch). After installing three diodes, so that the microphone could draw power from all three radios but without allowing the +5 volts from one radio get into another, the problem disappeared. One of those 'little things' that doesn't show up until you actually put an idea into practice!

Now everything was working fine until my friend actually drove the car! Yep, you guessed it. 'CBer's PL'...but I couldn't see how the alternator whine was getting into the transceiver's audio. I had brought the power for the transceivers directly from the battery and had even used a 30 amp relay to switch the rigs on and off with the ignition key...same as the regular car AM/FM radio. This allowed my friend to keep the audio volume controls in the same position and insured that all of the rigs were OFF when leaving the car, and ON whenever the ignition was ON. I even installed a switch on the radio console to select either the ignition switch or direct battery power to enable the relay. That way the radio stack could be powered up without the ignition key for those times when operating mobile at a fixed position (as might be done during extended public service duty).

In trying to figure out just what was causing the 'CBer's PL' problem, I did what every budding engineer (?) does when he has a problem. I talked it over with anyone who would listen! Following the suggestion of another technically-oriented ham-friend, I disconnected the two unused cables mic that run between the switch box and the transceivers, leaving only the active one in use. No help. Of course the alternator whine was gone with the microphone connected directly to the transceiver, by-passing the switch box entirely...but the switch box was such a neat idea!

So one weekend, armed with a portable scanner receiver set to the transmitting frequency in hand, I decided to get to the bottom of the problem. First, I found that removing the metal box from the radio stacking bracket (i.e., simply ungrounding it from the vehicle's frame), eliminated most of the noise. Interesting! Now disconnecting the unused radios removed all the rest of the annoying whine. Even more interesting! It turns out that what I had done, was connect all of the grounds together inside the switch box and then grounded them to the metal switch box itself, so that everything would be shielded from any source of noise. So much for that great idea! Instead, I now disconnected all the grounds from each other and from the box ground, and routed them through the rotary switch instead (fortunately, I had an extra set of contacts to do it). Now none of the microphone cable grounds were connected to the switch box or to each other any longer...and that turned out to be the final cure.

.

Here's what was happening? As we all learned in basic electricity, electrons will take any and all paths available to them to get to wherever they are going. Now since the alternator is mounted on the engine, and thus grounded to the engine, and the vehicle's negative battery terminal is also grounded to the engine via a nice thick cable, a classical ground loop was set to exhibit itself. And it waited there patiently just for me to come along!

The bulk of the alternator's ground current will travel via the heavy cable to the battery. But what I had done by grounding the switch box to the radio stack bracket, was to provide another path for the electrons to get to the battery via the car frame ground in the switch box, then to the transceivers via the microphone cables, and finally to the battery via the transceivers' power wiring. Admittedly, the actual current through the microphone cable was probably small, but not all that much is needed since the microphone is a low-level circuit, whose audio is greatly amplified...along with any noise in the form of alternator whine. End of mystery!

If you would like more exact details on how I connected everything up, or on where I found the parts to do it, etc. just send me a SASE (self-addressed, stamped envelope) I'll tell you all about it, perhaps more that you care to hear! I hope these tips and experiences prove helpful at some time to other 73 readers."

Moderator's note: Interesting story, Gary, thanks for sharing it with us. Gary's experiences are a good lesson for us all to keep in mind. It pays to watch for those sneaky multiple ground paths, especially where very low level audio circuits are concerned. It also illustrates how every problem has a solution with a regimen of logical thinking and practical troubleshooting approaches. Sleeping on it often helps too!

Cleaning pots...but not pans

Here's another solution from Richard Measures, AG6K, of Somis, California: "Noisy or intermittent front panel control potentiometers on today's ham transceivers can sometimes make operating frustrating instead of the joy it should be. The reason for the intermittent pots can often be traced to the grease originally used to lubricate them becoming sticky and gummy with age and the effects of oxidation. This in turn causes the contact between the rotating wiper-arm and the resistance-film to suffer, making poor, or even no contact at times.

One cure is to stand the set up on its back, using thick padding or the original packing foam as a protective cushion, then carefully removing the knobs from the offending controls. Using a syringe with a small-guage needle, inject TCE degreaser down into the clearance spaces next to the concentric shafts of the pot or pots that you wish to clean. Once the degreaser has penetrated, rotate the shafts back and forth a number of times to work the cleaner in and to loosen the gummy grease. When the pot has been thoroughly "exercised", inject a bit of GC Electronics deoxidizing cleaner or one of the other newer products that are now on the market. The GC Electronics material can be thinned with about 50% TCE to help it penetrate down into the tiny clearance areas between the pot's shafts if necessary. Caution: TCE is considered to be carcinogenic and should be used only in a well ventilated area, with tools and hands thoroughly cleaned afterward; wearing disposable latex gloves will help to protect you even more effectively by preventing absorbtion into the pores of your hands.

Once you've completed the proceedure, turn the set back on and check for any further intermittent action in the cleaned pots, repeating the operation if needed. This is a good deal quicker and less costly than replacing the potentiometers, and should keep them working properly for a number of years to come."

Moderator's note: Pots on equipment used in a mobile environment may need this treatment even more frequently due to the rigors of heat, cold and dust that are often present in a mobile installation. In fact, even fairly new rigs will exhibit very "stiff" control action when the winter temperatures drop below zero in the northern areas of the country, often requiring this "de-gumming" sooner than home-based equipment. Radio shack now sells several cleaning chemicals that can also be tried, some are "plastic-safe" as well as EPA approved. Another brand worth looking at is made by Caig Laboratories of San Diego, CA (1-800-224-4123 or 619-451-1799) and goes under their brand name of DeoxIT (reg. trade mark). DeoxIT is a deoxidizing solution that cleans, preserves, lubricates and improves conductivity all in one treatment. Using the proceedure outlined by Rich, however, will pretty well assure you of getting the cleaner into the right spot, not everywhere else that you don't want it to be!

Good labels

Phil Salas AD5X of Richardson, TX offers these tips: "For labeling front panels on my home-brew projects, I create a full size front panel sheet on my computer with all the labeling neatly done, and then I print it out on a laser printer. I make the sheet slightly smaller than the front panel itself, then cover it with clear shelf paper lining...with enough overlap to hold it to the front panel. This clear shelf paper lining is very inexpensive. You can usually buy a large roll of it at most grocery stores, in the kitchen sundries section, for about $3 or so. The switches, indicators, connectors, and so forth on the front panel itself will contribute to holding the sheet firmly in place. You could also apply some type of glue to the back of the paper though Iíve not really found that to be necessary."

Moderator's note: 3M (reg trade mark) also make a Scotch (reg. trade mark) brand double-stick tape that may work in conjunction with Phil's suggestion. It's their No. 66 series tape and is available in most office supply stores. It's a clear film tape that's adhesive on both sides, and small strips of it can be placed on the back of the areas where a wide expanse might otherwise result in buckling. I've also used the clear, self-adhesive covering made by Contact (reg. trade mark) as a protective film for panel labels and other paper surfaces that you want to preserve from wear and tear. It can usually be found in most hardware and variety stores.

Color me DEKA

Here's a colorful tip from George Primavera WA2RCB for changing the hue of incandescent lamps used in radio LCD edge-lit displays, meters, dials any many other applications: "My Kenwood TM-241A 2-meter rig came with the standard edge-lit LCD display. The first thing I noticed was that the white incandescent edge-lit LCD was a bit distracting in the car at night, even with the dial dimmer turned down to the low back-light setting. What it needed was a coloration on the edge-lighting bulbs that was more night-vision-friendly! A trip to our local art supply store netted a variety of colored (but still transparent) glass paint bottles under the "DEKA" brand name (made by Decart USA Inc., Lamoille Industrial Park, Box 309, Morrisville, VT 05661). DEKA is a color base 'paint' used by artists to paint pictures on glass, but I found that the 'paint' could also be useful for adding a nice color-tint to the miniature incandescent lamps used in my 2-meter rig.

The procedure itself is very easy. First remove the bulb(s) that you want to color-tint, then grip them by their wire leads using an alligator clip. With the leads pointing up, dip the bulb directly into the bottle of glass 'paint', taking care to not get any paint on the wire leads themselves...the bulb should be dipped into the paint up to about 3/4 of it's length.

Now touch the tip of the bulb to a clean piece of metal once or twice to remove any excess paint from the bulb's tip-end, then wedge the alligator clip holding the bulb under some heavy object (miniature organizer drawers work well) to hold it in place. The bulb should be suspended in 'midair' and allowed to dry overnight (generally 8 hours is the minimum drying time depending upon temperature and humidity). Next, simply reinstall the bulb back into the radio from whence it came, reassemble everything and turn it on. My TM-241A now sports a nice pumpkin-orange tint on its LCD, thanks to the newly colored backlight. It's noticeably less distracting while driving at night now in a mostly darkened passenger compartment.

A few precautions on this procedure should be mentioned: DO NOT color-tint any lamp larger in size than 3 watts nor one that normally gets warmer than you would be able to touch safely while in operation. I've had no problems with the grain-of-wheat bulbs used in radios, or with #47 pilot lamps used as panel indicators, but automotive type lamps (such as 1157) get much too hot, The paint will flake off from the excess heat in just a short time. Also, NEVER apply this treatment to ANY kind of halogen lamp. Halogen bulbs must be meticulously free of any foreign substances on their glass or they can shatter violently! The colors that I've found to work best are #30-Light Blue, #27-Orange, #26-Lemon and #28-Light Red. Note that lamps treated with the #30 Light Blue color will have a reduction of about 60% in their visible light output.

I'd recommend using this procedure on 'glass' bulbs only unless you try it on a 'throw-away' first. Plastic encapsulated light devices, such as LED's, might be chemically attacked by the solvent-base of the glass paint."

Recycled tubing

No one enjoys a stay in the hospital, but hereís a tip from Bob Boehm N8EXF of Cincinnati, OH that will at least make it a bit more practical from a ham radio standpoint: ìThe plastic tubing used in hospitals and nursing homes can often have applicability to our hobby! The rippled hose (usually between î and æî in diameter), used for oxygen transfer to a patient, can often be salvaged for use as a plastic ëconduití for running cables in your ham shack or perhaps in a mobile installation. The hosing can be used ëas isí, or slit with a sharp knife along its length, so that wires and cables can be tucked into it and given additional protection in harsh environmental areasÖor maybe just to keep those wires and cables a little neater looking for appearance purposes.

Likewise, the smaller diameter plastic tubing used for intravenous feeding, etc., makes great insulated, protective tubing for a number of ham and electronic applications. I use a length of it over my HF mobile whip antenna to act as a cushion between the ëwhippingí antenna radiator and the painted body of my van. The thick plastic tubing keeps the bouncing whip from marring the paint job on the back of my van very nicely. Generally, these ëhospitalí throw-awaysí are made of good quality plastic material and should last for a number of years of exposure to the extremes of weather and friction. Give it a try.î

Moderatorís note: I like Bobís idea ÖI saved some of the small tubing from my own hospital stay a number of years ago and have used it in numerous applications since that time. The lengths are usually long enough to protect a vertically rising wire antenna wire from direct contact by the ìinquisitiveî fingers of neighborhood children (or paws of pets) and you surely canít beat the price!

Murphy's Corollary: Everyone has a fool-proof scheme. It's easy to spot...it's usually the one that isn't working!

A very special thanks to this month's contributors:

Gary Holoubek WB6GCT

1961 Evergreen Avenue

Fullerton, CA 92635

Richard L. Measures, AG6K

6455 La Cumbre Road

Somis, CA 93066

Phil Salas AD5X

1517 Creekside Drive

Richardson, TX 75081

George Primavera WA2RCB

830 Park Drive

Cherry Hill, NJ 08002

Packet address:

WA2RCB @ KE3CZ.#EPA.PA.USA.NOAM

Bob Boehm, N8EXF

6821 Le Conte Avenue

Cincinnati, OH 45230-2935

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.

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).