Ham To Ham #17 - February 1997

73's Ham To Ham column

c/o Dave Miller, NZ9E

7462 Lawler Avenue

Niles, IL 60714-3108

Just a reminder to keep the "Ham To Ham" column in mind whenever you run into an interesting solution to a problem in your pursuit of amateur radio. I need lots more input to keep the column lively and interesting. Any idea, suggestion, tip or solution is fair game...as long as it has applications to the hobbies of electronics and ham radio. We've all discovered unique approaches and resolutions to our common problems, and "Ham To Ham" is the ready forum for sharing them with other 73 readers. Just jot down your ideas and send them to the address above, I'll let you know if I can them and roughly when they'll appear. Include an informal sketch if you feel that would help explain your suggestion and a short text (handwritten or typed) and I'll take it from there. I'll put it into the tone of wording that I've been using for the column and redraw the illustration if needed, so don't let formality hold you back. Now to this month's ideas.

Cable ID's

Here's an easy-to-duplicate tip from Dave Hyman KB0ONF: "Time to start saving those little square plastic closures often found on plastic-wrap bread bags these days...they make nice cable identification tags. A drop of lacquer thinner will remove any printed matter on the tags, and a sharp, black permanent marker will allow you to write your own information in its place. They fit nicely on most sizes of cabling found around the average ham shack, but the hole can also be enlarged a bit with a hobby knife if needed. If the tag refuses to stay on a particular cable, try putting a small piece of good quality transparent tape across it's bottom 'split-edge'."

Moderators note: Nice idea, Dave...does anyone have any other favorite cable marker schemes? Here's something to compliment any cable marking idea: instead of trying to put all of the information needed on the tag itself, use a "cable schedule". A "cable schedule" is simply a form (make up one and photocoy a bunch of them) that shows a cable's number (such as #100), the type of cable (RG-8X coax), the source (FT-1000MP Antenna Jack), its destination (Linear Amp Input Jack) and its purpose (RF feed from transceiver to linear). A single 8 1/2" X 11" piece of paper will easily hold the information needed on 20 or so cables when oriented in the 11" (landscape) direction. A cable schedule allows you to simply put just a cable number on each end of a cable, rather than trying to describe what the cable's function is on a rather small tag...that's all done on the schedule form sheet instead. The cable schedule form gives much more informaton than would ever be possible otherwise, and also permits you to easily change the function of a cable when redesigning your station...only the entry in the cable schedule form itself need ever be changed. We used cable schedules extensively in broadcast installations, considering the cables more or less permanent, and only their functions as changing. Do it in pencil. It's very logical and flexible once you've become used to it, but you do have to conscientiously keep it up to date if it's to be of value.

Cleaning up "after" a hamfest

Here's a good, clean tip from Mark Marholin KE6JJR: "You can often make those not-so-attractive 'hamfest specials' come back to appearing close to new, by simply mixing some hydrogen peroxide and water as a cleaning agent. Hydrogen peroxide is very inexpensive, and can be obtained at any drug store, but it does a nice job of cleaning grit, grime and tobacco smoke stains from a piece of equipment. It also kills bacteria and breaks-up organic matter...that might have been an unexpected bonus...with its bubbling or cavitation action. The exact proportions can be arrived at experimentally, but a 50-50 blend is a good place to start, since the typical consumer-available hydrogen peroxide is usually only about 3% strength. Give it a try and see how it works for you. By the way, it's also used as a bleaching agent, so avoid getting any on your clothing."

Moderators note: I've kept a bottle of hydrogen peroxide on my workbench for years for applying to small cuts and scrapes to my hands, because of its anti-bacterial properties ... an M.D. friend told me about it long ago. Mark's tip is just another reason why hydrogen peroxide may deserve a reserved spot on your bench. I've also found Dow brand foaming bathroom cleaner (available at most supermarkets) to be very effective in cleaning particularly grimy equipment panels and cases. It too has a cavitation action that breaks away stubborn collected material, but test it first on an out-of-the-way spot to make sure that it's compatable with the paint and silk-screening used on your rig...you don't want to "clean away" important information!

Reducing heat build-up in tube amplifiers

Here's a good winter-time project from Richard Measures, AG6K, of Somis, California:

"Excessive heat build-up, within any piece of ham radio gear, can greatly affect the trouble-free equipment life-expectancy period of that equipment. In case you're in doubt, it's generally accepted that electrolytic capacitors can be expected to decrease in life-expectancy by one-half, for each 10 degree Celsius rise in temperature (18 degrees Fahrenheit rise) above normal room temperatures. This alone should be enough to convince most of us of the importance of keeping the tube compartments in older HF transceivers, and in amateur linear amplifiers, as free from heat build-up as possible.

Another reason is the often self-destructive effects that too much heat can have on higher-power amplifier tubes themselves - such as the popular 3-500Z's - used in many ham linears. These tubes will normally run with a orange glow on the anode material, with the expectation from the tube's designer that much of the internal heat will be dissipated by means of radiation and absorbed by the cooler surrounding metal chassis structure. Just as often, however, those surrounding metal parts are shinny, reflective, aluminum or steel, sending a large amount of that radiant energy right back into the tube instead of dissipating it as the designer hoped would be the case.

By painting the inside of these tube compartments a flat-black, considerably more of the radiant energy will be absorbed and safely carried away, than if the metalic surfaces are reflective and force the energy to bounce back and forth between the tube(s) and the enclosure. This is a simple point of physics that some product design engineers overlook...bright or shinny surfaces always reflect, and dark, dull surfaces always absorb radiant energy...and heat is radiant energy. Kenwood's TL-922 linear amplifier, as an example, does indeed have flat-black tube comparment walls as it should.

If your particular amplifer doesn't, black liquid shoe polish is one simple answer. Evenly applied to all of the reflective compartment surfaces, especially those that would relfect radiant energy right back into the tubes themselves, is time well spent. This simple step alone will help the equipment's cooling fan to do its job, and help to keep your gear functioning longer, cooler and more trouble-free."

Moderator's note: I've applied Rich's idea to my own Heath SB-1000 and can vouch for it's effectiveness. I painted the internal walls of the tube compartment with flat black paint and immediately noticed a substantial increase in the amount of heat absorbed by the comparment walls...heat, by the way, that very little of which will find it's way back into the 3-500Z itself. What modification could be simpler? Just make sure that the power is unplugged and the power supply's capacitors are completely discharged when you're working inside of any compartment that carries high voltage. I always clip a jumper from the anode of the tube to ground whenever my hands are in or near the final RF compartment. I learned the value of that years ago when working inside of broadcast transmitters. "Inside" is the right word, you could actually walk inside of our VHF TV transmitter!

Workbench pin-up

Figure 1 shows a handy nomogram from John Nix of Foley, MN, to keep near your workbench. The dictionary definition of a Nomogram is "a graph that enables one, with the aid of a straightedge, to read off the value of a dependent value when the values of two or more independent variables are given." John's allows you to quickly approximate the equivalent value of two or more parallel resistors or two or more series capacitors. Simply lay a straight edge between the values that you want to combine on the top and bottom angled lines (Scales A and B), then read the equivalent combined value on the straight line in the middle (Scale C). It's much faster and easier than struggling with the all of the division needed for the "standard" parallel resistor or series capacitor equivalency formulas (also shown in Figure 1).

For instance, a 270 ohm resistor in parallel with an 820 ohm resistor is 203 ohms. A .022ufd. capacitor in series with a .047ufd. capacitor is .015ufd. Remember that the value will always be lower than the lowest of the two individual component values for resistors in parallel and capacitors in series.

To solve for multiple resistors in parallel or capacitors in series, simply use the first two values and find the equalivant on the nomograph, then use that answer plus the third value for the next equalivant and so on until all of the values have been accounted for. The final value is the overall equivalent circuit value of all of the components in that parallel (resistor) or series (capacitor) circuit.

Note: The Nomograph in Figure 1 is only useful for values within the same power of ten, ie., when all of the resistors in a parallel circuit are in ohms, hundreds of ohms, thousands of ohms (K), etc. To find the equalvant of a 470 ohm resistor in parallel with a 10K ohm resistor, best use the longer formula (by the way, the answer is 448.9 ohms!). Thanks for another nice chart John.

Big dipper

Here's an interesting idea that you might want to try from Phil Salas AD5X of Richardson, TX: "For waterproofing outdoor connections and connectors, Iíve had very good luck with a product called 'Plasti-Dip' (reg trade mark). It's a fast curing liquid plastic material that's intended primarily for coating tool handles. A can of it costs about $7 at Home Depot (reg trade name) 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 out-of-doors 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 with hot glue (hot glue guns are great for a lot of things like this). Then I attach solder lugs to the ends of the shield and center conductor as the connection point to the antenna's balun. Finally I dip the entire end of the coax (including the solder lugs) into the Plasti-Dip and let it cure. After curing, I'll use a hobby knife to trim off the excess Plasti-Dip insulation that covers the ends of the solder lugs. Neat, easy and if done correctly, effectively waterproof!"

TTT (TRANSFORMER TEST TIP)

Here's a tip for easily and accurately testing the insertion loss of transformers, whether they might be AF transformers or RF transformers. Testing the actual dB loss in step-up or step-down transformers is tricky because of the different impedances presented by the primary and secondary windings...dB loss formulas assume like impedances on the input and output of any device where dB gain or loss is to be calculated. But with transformers, this criteria is easy to meet, simply by using two identical tranformers (same type number) and hooking them up back-to-back (see Figure 2). Now the input and output impedances are identical, so the loss can be measured by simply comparing the differential in voltage between the input of the two and their cascaded output, then dividing that result by two. If your measurements indicate a 6dB loss using two identical transformers back-to-back, it's safe to assume that each is responsible for 3dB of that loss...certainly closely enough for all but the most exacting applications.

de Dave, NZ9E

Hidden QRP wattmeter

Here's a clever idea from Ken Guge K9KPM of Lombard, IL for finding a "hidden" QRP wattmeter on your operating desk: "Wanting to accurately measure the 2 watt RF output from my Kenwood HT, my eyes immediately came upon the Daiwa CN-550 cross-needle VHF SWR/POWER meter sitting on my operating bench. The Diawa CN-550 measures forward and reflected power directly in watts, with two separate meter needles, and then it "computes" (on the meter's scale) the SWR by where those two separate needles cross. I'm sure everyone's seen this type of meter even if you don't currently own one. The forward power scale has a range of zero to 20 watts on its most sensitive range, but even at that, the 2 watt point for my HT's RF output is only about the lower one-fifth of the full 20 watt scale markings...okay, but not great for accurate QRP measurements.

In thinking it over, it occurred to me that the reflected scale, zero to 4 watts, would be the perfect one to use, with the zero to 2 watt portion on the scale covering about three-quarters of the meter's range...several magnitudes better than the forward scale. It's amazingly simple to use that reflected scale for measuring low power outputs, simply hook the unit up backwards!

Instead of HT's output cable going to the "TX" connector on the CN-550, connect it to the "ANT" connector instead. Then put your dummy load (a low power one is fine) on the "TX" connector of the meter. You won't be able to see your SWR correctly, but you no doubt already know that your dummy load is very close to 1:1, so it's no loss. What you will see though, is your forward power...now on the "reflected" scale...in far greater detail! Small adjustments can be made to your low power HT and the results will be easily visable on the zero to 4 watt right-hand reflected scale. You've just uncovered your "hidden" QRP meter and you didn't even have to lift your soldering iron to do it!"

Moderator's note: I've had a Diawa meter like the one that Ken mentioned above for years, and never really saw it in that light! Ken's idea clearly illustrates what "ham ingenuity" means, looking at an item from another point of view and "inventing" a new use for it. Of course you can apply the idea to any of Diawa's (or others) dual-needle meters, in any frequency range. Another nice tip, Ken.

That wraps up this month's Ham To Ham column; does anyone have any ideas on "different" uses for common items such as K9PKM gave us? Send them, or any other ham-related tips, ideas, suggestions or short-cuts to me at the address in the masthead, and I'll share them with the rest of 73's readers. That's our purpose, sharing practical ideas Ham To Ham.

Murphy's Corollary: Explaining something so clearly , and in such detail, that no one could possibly misunderstand it, will inevitably guarantee that someone will.

Many thanks to this month's conributors, including:

David L. Hyman KB0ONF

1455 Edgcumbe Road

St. Paul, MN 55116

Mark Marholin KE6JJR

1588 Four Oak Circle

San Jose, CA 95131

Richard L. Measures AG6K

6455 La Cumbre Road

Somis, CA 93066

John Nix

9123 Highway 23 NE

Foley, MN 56329-9501

Phil Salas AD5X

1517 Creekside Drive

Richardson, TX 75081

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 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).