Ham To Ham #15 - December 1996

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

It's the December issue already, and probably the right time to turn most of our concentration toward warm indoor activities, at least here in the frozen northland!

Net Nite Adventures!

From William Thim, N1QVQ: "This idea may not be totally new, but bears repeating just in case some may not have heard of it...it concerns some operational suggestions for "Emergency Practice Nets".

When the net control station feels that his or her net members are ready, try not starting the net on time and see what happens! You should have a back-up net control station...how long will it take your back-up to jump in and assume control of the net? On a different occasion, pre-arrange with your back-up to also not take over...then see how long it takes for one of the participants to assume the reins. These "readiness" tests may seem a bit deceitful at first, but they are good hallmarks of the net's ability to "run itself", as it well might have to, during an actual emergency.

We all get used to having things happen in a comfortable, familar way, but that's not always to be expected in a true emergency situation...because emergency - by it's very definition -is itself unpredicatable.

Here's another test...try telling all of the check-ins that your emergency battery power is failing, to please recheck-in again five minutes from now...and then see how many actually do. During actual emergencies, you may not have time to fully explain a situation and the net members will have to comprehend something unusual quickly, and follow your suggestions without any further guidance.

Still another good test would be to tell everyone that they've just lost their normal antenna set-up and to check in as soon as they can on their back-up antenna...however simple that might be. Perhaps some stations will have to relay for others who can't be heard by net control...how well is this handled?

Finally, and this test applies to VHF/UHF repeater emergency nets, announce that the repeater will be turned off, simulating a loss of power at the repeater site. Again, stations will have to be ready to relay for each other and be able to copy weak and noisy signals from around the normal net area, proving that in actual emergencies, copy may not always be "arm chair clear" during times of distress. How well does this work?

There are probably many more "test-worthy" scenarios that could be explored by inventive emergency net control op's and members alike, that will add realism and "adventure" to what might otherwise be "routine" net nights...while also providing a truer yardstick of how well your emergency net "really is trained" in its own emergency preparedness."

Paddle your batteries

From Ken Guge K9KPM comes this handy idea: "Have you ever wanted to measure the current drain from a particular piece of ham gear, or perhaps your daughter's portable tape player that's driving you close to the poverty level with AA batteries? I often thought that battery manufacturers ought to give these things away just to keep you in the high-volume battery-purchasing market. Well here's an easy way to put a milliammeter in series with those cells, without having to cut into the circuitry itself.

Take a piece of scrap double sided printed circuit board material (about 1/2" wide by 1-1/2" tall, and solder a short length of stiff wire on each side of the double-foil-sided board. These will be the "quick" connection points for your VOM. Next, on the opposite end, file the 1/2" side down to a "chisel shape", so that it will slip easily between two of the series connected cells in the spring-loaded holder (see Figure 1). Now, when you insert this "Battery Paddle" into the pack, you'll interupt the current flow...but then hooking up your milliammeter will restore the flow and give you an accurate estimate of how much the little battery-eater is drawing.

You can use this as a trouble-shooting aid and know right away when you've cleared a high-current-drain problem...or use it simply to check the battery drain for the sake of curiosity.

If you make two of these paddles, you can insert one at each "end" of the series battery circuit, so that you can hook-up a charger to the "cell-side" of each paddle (being careful to observe the correct polarity), if you've decided to stop buying throw-away cells and use rechargables instead.

If you hook up a test power supply to the "equipment-side" of each paddle, (again, observing correct polarity) you can power the item from that external supply instead of the internal battery cells for those times when it might receive extended-use.

I hope that this idea proves as useful to others as it has for me."

Moderator's note: Good tip, Ken...by the way here are some typical Milliamp-Hour typical figures for alkaline-manganese dioxide cells, directly from Duracell (registered trade mark):

AAA - 1,120 mAH

AA - 2,450 mAH

C - 7,000 mAH

D - 14,250 mAH

9V - 565 mAH...below are some typical mAH capacity figures for 9 volt batteries at different current drains:

600 mAH @ 5 mA drain

560 mAH @ 14 mA drain

546 mAH @ 26 mA drain

You can see that the mAH figures will vary a bit depending upon the actual current drain, higher current drain giving less Amp-Hour life, but they're still a good guidepost for general usage. When you measure the current drawn by a particular piece of equipment, using Ken's battery paddle idea, divide that figure into the total capacity shown above for the size of cells you're using, to get an approximate idea of the number of hours of use to be expected from those cells.

No drip 9913

Chuck Steer WA3IAC offers this suggestion: "Belden 9913 (reg. trade mark) coax cable - and its clones - have been known to change from a nice dry transmission line into a water pipe, after repeated soaking rains compliments of Mother Nature. This can be the combined result of the cable itself having an internal "air" dielectric, coupled with a non-water-tight fit between the cable and its outdoor connector.

I've solved the problem at my QTH by always using a length of 3/4" diameter heat-shrink tubing over the finished connector's back end, then wrapping the entire connection with Teflon (reg. trade mark) self-adhering tape. If you don't have a heat shrink gun, you can always "borrow" the XYL's stove for a few minutes to acquire the heat needed to make the shrink tubing good and tight over the rear of the cable/connector interface junction. Don't depend upon overlapping tape alone to seal this critical point."

Moderator's note: Chuck has a couple of good suggestions here...for the heat-shrink-tubing part, I've also had excellent results with the type of heat guns generally sold in hardware stores or home improvement centers - intended for use in stripping paint or for thawing frozen pipes. There's the large "gun" style and also a smaller "point-source" style (my personal favorite) that will handle most jobs around the electronics workbench. They're usually quite a bit less expensive than heat-guns sold specifically for heat-shrink-tubing applications alone, so if it's dropped, the loss isn't as great. I use one of the small "point-source" heat guns for applying concentrated heat to a circuit part that I suspect of being overly heat-sensitive...in general troubleshooting as well.

Recycling is "in"!

73 reader Andrew Gretchenuk sent in this innovative idea, along with the samples shown in Photo 1: "Whenever I go to a garage sale, house sale or flea market, I keep an eye peeled for any enclosures that might have ham radio or electronics applications. One of the ones that I particularly watch for is normally used in the kitchen, and consists of three or four wooden canisters of the style that 'nest' inside of one another for storage. They often make great little speaker enclosures or general radio project housings (for receivers, meters, test gear, etc.). To adapt them to a project, I'll usually use the scheme shown in Figure 2...to give me a metal 'partial chassis' for parts mounting. The spacers shown in Figure 2 can often be picked up at hamfests, or you can obtain them from parts suppliers such as Fair Radio Sales of Lima, Ohio (Tel: 419-227-6573) or The Electronic Goldmine in Scottsdale, Arizona (Tel: 1-800-445-0697). They can be obtained in various lengths from 1/4" on up. Another item to watch for at second-hand sales are metal cookie or candy tins...when repainted with metallic automobile spray paint, they often end up looking very professional and make excellent shielded enclosures (also shown in Photo 1)...most are even directly solderable when buffed up a bit and soldering paste is applied."

Moderator's note: All good suggestions, Andrew, and thanks for sending the samples for photographing. Another source of handy very small "recycled" cases are those used to package "tic-tac" (reg. trade mark) brand breath mints...they'll hold a miniature remote toggle switch, a few small parts or will act as a cable splice junction box. Either leave them transparent or apply a quick spray of your favorite color of "ham gray". It's best to put the mints inside of something else that doesn't make so much noise in your pocket anyway!

Dave, NZ9E

Pinned to the mat!

Here's a very clever idea from Herb Foster, AD4UA:

"When the need arises to 'hide' radial wires or a small coax feed cable for an HF 1/4 wave vertical out in your lawn, here's a tip to keep in mind, one that I've used myself very successfully. Of course you can drag out the shovel and split open the ground wide enough to accomodate those radial wires or RG-8X coax, but why not let nature do some of the work for you instead?

Gather up a handfull of wire coat hangers, the ones that seem to accumulate in closets as if they're breeding there! I can't recall ever even paying for a wire hanger...my XYL always seems to be able to produce a nice bunch for me upon request. Once in hand, use a sturdy cutter to clip off the hanger's normal 'hook' and straighten out the remaining length. Next, cut this straightened piece into 9 or 10" lengths and form a 90 degree (or more) bend...about an inch or so from one end... in each of these smaller lengths. Make up a bunch of these 'cable pins', and push one down into the earth about every 15" or so along the radial or transmission line run...the one inch bend will 'pin' the wire closely to the ground and keep it there. If you've mowed the lawn somewhat on the 'short side' first, so much the better...the grass will grow up around the 'pinned-down' wire and your radials and transmission line will eventually almost disappear into the lushness of the turf. If done correctly, you'll be able to mow right over the radials and coax as if it weren't even there. This tip works equally as well at your home QTH as it does at a temporary 'ham-cation' spot!"

A better cube!

Here's a tip from Stephen Reynolds N0POU that you might want to try:

"Most of the inexpensive wall-mount plug-in DC power "cubes" that are available today have no internal regulation and will often sag to close to 50% of their labelled voltage when loaded to near their labelled current rating. Some items of equipment (if they have their own internal regulation) will work correctly when powered by these 'cubes', but other items won't. Applying too much or too little voltage to certain accessories can be risky at best...but here's a way around that potential (ouch!) problem!

DC to DC automobile cigarette lighter adapters can be found that will lower and regulate the normal 12 volt DC car battery potential down to some other (often selectable) value ... and these little gems can also be used on the 120 volt power 'cubes" mentioned above. Just be absolutely sure that you observe the correct input and output polarities, and that the current drain expected doesn't exceed the rating on either the power 'cube' or its DC to DC regulator add-on. Take a look at the Radio Shack (reg. trade mark) catalog if you've not seen the DC to DC adapters I'm referring to, they show several that are applicable."

Moderators note: You might also consider building up a small external regulator using one of the many fixed voltage regulator chips on the market today. They're available in several size and current ratings and are extremely easy to put to use. The 78xx family of 1 Amp positive voltage regulators in a TO-220 case (as shown in the drawing of Figure 3) can be commonly found in these standard fixed output values:

7805T - 5 volts

7806T - 6 volts

7808T - 8 volts

7812T- 12 volts

7815T - 15 volts

7818T - 18 volts

7824T - 24 volts

You can also incorporate an adjustable regulator, such as the LM-317T, shown in last month's coulmn.

Fabulous ferrite

From Jim Kocsis WA9PYH comes this interesting tip:

"Have you ever noticed how generally poor the AM sensitivity is on most of today's small portable transistor broadcast band radios? The sensitivity on the FM band is usually much better, because the FM band uses either a telescoping whip antenna or perhaps the fairly long headphone cord, allowing the capture of a reasonable amount of usable signal...but the AM band is a whole other story.

The sensitivity on AM is limited by the effectiveness of the built-in ferrite rod antenna used for AM band pick-up, and as the size of the radios have been shrinking, so has the ferrite rod's length...often ending up to be only a couple of inches long. I have a "super" AM radio that contains an 8" long ferrite rod antenna, and it runs rings around the smaller radios...primarily because of the longer rod.

Not wanting to have to carry the larger radio around, I decided to experiment a bit. I tried positioning just a ferrite rod, about 8" long, at various points around my little radio's case and found that reception could be markedly improved. You can find these larger ferrite rods at hamfests, garage sales or fleamarkets...the salvaged parts of older AM radios or perhaps the entire defunct radio itself. Simply strip off the coils of wire, then find the best spot on the outside of your small AM portable...where the signal is enhanced significantly...and using a rubber band to hold the 'auxiliary signal booster' in place, get ready for greatly improved performance. The flat ferrite form will give you the lowest profile, of course, but the round rods work well too. Be careful handling the ferrite material, it's very brittle and will easily snap if dropped or mishandled. Give the idea a try, it might just make you the 'hero of the day' to your wife or children (grandchildren?)."

New pin-up beauty

John Nix sent in this update to the "pin-up beauty" resistor chart...thanks John:

"Standard resistor value spacings are somewhat more complex than would be indicated by chart shown in the Ham To Ham column for August 1996 (Page 51). The actual

relationship for standard resistive values is outlined mathematically below and illustrated below and in Chart 1:

20% resistors are spaced in steps of the 6th. root of 10

10% resistors are spaced in steps of the 12th. root of 10

5% resistors are spaced in steps of the 24th. root of 10

1% resistors are spaced in steps of the 120th. root of 10

Here are some equally handy relationships to remember for standard (B&S) wire gauges:

When you drop down three gauges, you end up with half the cross-sectional area and twice the resistance. Going down six gauges, results in half the diameter, one-quarter the cross-sectional area and four times the resistance...and so on. These decreases (or increases) follow the same steps-of-three as do decibels of power, ie., 3 down = 1/2, 6 down = 1/4, etc. Makes it easier to remember.

These mathematical relationships aren't unique to electronics, of course. In musical terms, the 12 notes of an octave are separated by steps of the 12th. root of 2. Each octave

doubles the frequency in the upward direction or halves it in the downward direction.

Remembering a few of the basics allows you to compute many values when you need them ... anytime or anywhere ... just don't forget your calculator if you "just squeaked-through" your math classes in school!"

This ends another month of Ham To Ham. From KA9UCK (Sue) and I, all the best of the Holiday Season's joys and happiness. I hope that Santa brings you some interesting ham radio toys...remember gals, men like toys as gifts, not clothes! We're actually just little boys in bigger jeans!

And now that winter has set in to stay for a while, why not sit down and write a brief description of some of the things that you've found useful in the pursuit of your own ham radio interests? I'll share them with the other 73 readers through this column in the coming months. Items of interest for spring and summer projects would also be appropriate to send in now...magazine lead-times are fairly long. Please send all tips, suggestions, ideas and shortcuts to the address in the masthead. See you next year!

73, de Dave, NZ9E

Many thanks to our faithful contributors, including:

William Thim, Jr., N1QVQ

50 Miller Road

Broadbrook, CT 06016-9676

Ken Guge, K9KPM

1107 E. Woodrow Avenue

Lombard, IL 60148

Chuck Steer, WA3IAC

3446 Shelmire Avenue

Philadelphia, PA 19136-3525

Andrew Gretchenuk,

12233 Rosaro Avenue #1

Warm Mineral Springs, FL 34287

Herbert L. Foster, AD4AU

3020 Pennsylvania St.

Melbourne, FL 32904-9063

Stephen Reynolds, N0POU

510 S. 130 Street

Omaha, NE 68154

Jim Kocsis, WA9PYH

2217 Hidden Oaks

South Bend, IN 46628

John Nix

9123 Highway 23 E

Foley, MN 56329-9501

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).