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 #22 - July 1997
73's Ham To Ham column
c/o Dave Miller, NZ9E
7462 Lawler Avenue
Niles, IL 60714-3108
USA
E-mail: dmiller14@juno.com
Please keep your ideas, tips, suggestions and short cuts coming my way, either by "actual mail" or cyber-mail. Ham To Ham is a reflection of your interests and input, and its content is only as good as the support that I receive from you, the reader. So send your tips to either of the addresses shown above and there's a very good chance that they'll appear in one of the future columns.
They're not just for PC's anymore!
With the current widespread use of multimedia PC's (personal computers), the availability of some pretty nice sounding multimedia speaker/amplifier units also exists. These speaker/amplifier units are often available at hamfests, computerfests or at discount outlets at very attractive prices, and we hams might well consider their use in other areas of our hobby... they're not just for use as multimedia PC sound drivers anymore!
PC speaker/amps can, for instance, be used in a noisy mobile environment to augment the sometimes difficult-to-hear audio from an amateur band hand-held portable transceiver or a portable scanner receiver. They can also be used within the home station to boost the audio from an amateur receiver, transceiver, DSP unit or other audio source that might need just a bit of extra uumph.
Many of these PC speaker/amplifiers will operate quite satisfactorily from their own internal battery power, but if you'd like to supply longer-term DC power from the 12 volt DC cigar-lighter outlet in you car, or a small 120 volt AC to low voltage DC adapter in your home shack, then
you may need to consider building a little circuit something like the one shown in Figure 1.
The schematic diagram of Figure 1 shows an adjustable low voltage regulator that can be easily constructed on a small piece of perf board, or even by directly wiring to the terminals of the regulator chip itself. It utilizes an easily obtained LM-317T regulator in a TO-220 style case (available from several of 73's advertisers), which will handle an amp and a half of output current (when properly heat-sinked), and up to 32 volts DC input voltage (the input must be DC, not AC)...then regulating that higher voltage DC down to 3V, 6V, 9V, 12V (or anything in between) for powering your PC speaker/amplifier.
Note (in Figure 1) that you may elect to make the regulator circuit either variable (by the use of a 5K pot for R1) or fixed (by choosing a suitable fixed resistor for R1 from the chart). If you don't intend to ever change the voltage, the fixed resistor option is the best choice because it will never change by itself (such as might happen were the pot to become "noisy"), and it's a bit less expensive to build it with a fixed resistor vs. a variable potentiometer.
Whatever source of power you end up using, it should be reasonably well-filtered (so that audible hum isn't a problem), and it should, of course, be able to supply the current needed by the speaker/amp with some overhead margin for safety. It must also be of positive polarity. Other than those precautions, you should find the circuit pretty much "universal" in its application. You might also find that you can run two or more speaker/amps off of one regulator "module", again, depending upon how much current is drawn by each...just be sure to stay safely under the 1.5 amp maximum limit of the LM-317T and assure that the chip is provided with enough heat dissipation mass so that it won't go into thermal shut-down (a condition wherein the chip shuts itself off due to too much heat buildup internally). The heat sink mentioned can be a piece of scrap aluminum or one of the black-colored, finned heat sinks sold specifically to fit TO-220 style chips. Silicon grease should be used between the chip's tab and the heat sink mass for the best possible heat transfer characteristics (and to prevent "hot-spots" on the chip's case). With the LM-317T, just be careful not to allow the heat sink tab (or anything connected to it) to come into electrical contact with common ground. The tab on the LM-317T is at output potential electrically so it must be isolated from the circuit common connection (negative DC lead).
The regulator chip has some built-in safety modes...too much heat buildup (as mentioned) and short-circuit protection (should the output circuit be accidentally shorted). One thing that these regulators won't tolerate is back-feeding a higher voltage into their output lead. This could happen if a battery pack of higher voltage is connected to the chip's output (without a blocking diode to prevent feeding the voltage back into the regulator) or accidentally connecting the regulated bus across another higher voltage circuit bus. I've seen regulator chips literally explode with a bang (and in many flying pieces) under these conditions!
Properly used however, it isn't difficult at all to implement an LM-317T into a universal regulator for powering almost any small accessory, including those bargain PC speaker/amps that often surface these days.
de Dave, NZ9E
Nearly FREE parts!
Speaking of bargains, here's a real bargain tip from George Primivera WA2RCB of Cherry Hill, NJ: "I recently encountered a failure of the external speaker jack on my Icom general coverage receiver. The jack was an 'Alps' (manufacturer's name) component, designed for mounting directly onto the PC board. The small square plastic shell which serves to hold the metal contacts of the jack assembly together, cracked across the top, rendering the little jack useless. Knowing that such a part was not the type normally available from convenience electronics outlets like Radio Shack (reg. trade name), I searched through the electronics mail-order catalogs, which had similar parts within their pages. Unfortunately, the problem with mail-order parts at times, is that, if you don't have the exact part number and/or the technical specifications of the part you need, you might not get a suitable replacement. Then I happened to look at a couple of old VCR's that I had salvaged from a nearby TV / VCR repair shop.
Most people now seem to throw away their old VCR's rather than fix them, and I had a few of these 'throw-aways' on hand for their spare parts value. A TV / VCR repair shop in my town was more than happy to 'clear their shelves' of a couple of these lifeless samples just for the taking. Guess what? The external audio jack attached to one of the scrap VCR boards was an exact replacement part for the one needed for my Icom! It was even made by the same manufacturer, Alps Electric Ltd.! Looking at the VCR board, it then became apparent that many of the same passive components (capacitors, resistors, jacks, pushbuttons, etc.) were identical to those used in my Icom. When you think about it, it makes sense; why use different production line components for ham radio equipment and those that are used in Japanese consumer goods like VCR's, TV's, cellular telephones and the like? While there are certainly some components - namely higher power RF parts - that won't show up in consumer electronics, many others do. Some just might be waiting for you to use, and for significantly less that the parts and labor costs you would have to pay if you didn't do the work yourself!
One final example...my Yaesu FT-23R developed an intermittent PTT switch recently. I happily
found an exact replacement for the Yaesu's switch behind the front panel of a scrapped Cannon
VCR I had picked up, free, at the local TV shop. The HT now works just fine, and the cost of
replacement parts was about as reasonable as it gets! So next time you need a part, you might consider looking at scrapped consumer electronics items. Of course it's always a good idea to pre-test the salvaged component before installing it in your ham equipment. Some of the newer VCR's also make use of many surface mount components, and these are a ready source for chip diodes, resistors and capacitors which are often needed for modifications to the newer, smaller ham gear. Look into these 'gold mines' and you might just save yourself a few hard-earned dollars (and not have to wait for the postman) the next time your ham rig develops a easily correctable fault."
Moderator's Note: A man after my own heart! Thanks for the suggestion, George. You'll often find scrap VCRs, etc. at hamfest these days as well. They're usually just a couple of dollars, or even free, if you just stick around til closing time. Many vendors would prefer not to lug the "no sale" items back home again.
Slippery characters!
Here's a tip you might like to try from Richmond B. Shreve Jr. W2EMU: "The shiny little plastic track ball pointing device used on many laptops, can develop a tendency to slip due to dust, skin oils and often from snacks we tend to keep close by while using our computers! I've found that adding some measure of texture to the surface of the trackball, however, can help to reduce this slippage problem quite a bit.
Here's one procedure: first, roundup a small (4" x 6") square of very fine sand paper. I used 220 grit, but a finer grit might be even better. Form the sandpaper into a tube slightly larger than the ball itself, with the gritty-side on the inside. Remove the ball from the computer's trackball housing and place it inside the tube with your fingers over the ends. Now shake...the tube, that is! As the ball travels back and forth inside the tube, all surfaces should become approximately uniformly roughened. It took about three minutes of shaking for a satisfactory result when I tried it.
This procedure leaves the ball rough and gritty, but we're not done quite yet. To change this to a smooth but textured surface, place a small amount of toothpaste in the palm of your hand and "massage" the track ball with it, taking care to rotate the ball so that all areas are equally burnished. Most toothpaste's have a slightly abrasive component that helps to clean the tooth surfaces and it will do the same for the plastic trackball.
Now, after thoroughly rinsing and drying the ball, set it aside for a few minutes while you clean the socket. I found that regular drug store eyeglass cleaner on a cotton handkerchief works well for this. Also clean the little rubber wheels that the ball rides on in the trackball housing itself...the little wheels that generate the vertical and horizontal movement of the cursor. Blow away any residual lint from inside the housing and re-install the ball and its retaining ring.
The ball action may have a somewhat gritty feel now, but will be far less easily affected by the oils and dirt that can lead to slippage, in the future."
OOPS!
This tip comes from Bill Turner W7TI: "Oops, there goes a cup of coffee right across the front of your new ham transceiver! It's a good thing that it wasn't turned on, though you still have the unpleasant job of cleaning it up...but what's the best method?
Believe it or not, water (and a little mild detergent, if necessary) can often be the most effective method. Where I work, we wash PC boards each day, using a special detergent made for that purpose, as part of our routine cleaning procedures...and it works just fine. The key is to make sure that everything is thoroughly dried afterward, and as quickly and safely as possible. We dry the washed boards in a 170 degree (Fahrenheit) oven for 30 to 45 minutes.
Depending upon where you live and the amount of minerals in your local water, you can probably get away with using ordinary tap water for the bulk of the cleaning, but always use distilled or de-ionized water for the final rinse. Distilled water is readily available in most supermarkets these days...Perrier Water (reg. trade mark) isn't necessary, HI!"
Moderator's note: Bill's methods can be the simplest and most effective way to handle this "sticky" problem! I've used similar procedures on really grimy items of electronic gear, but you have to be careful. Complete removal of easily damaged parts may be the safest approach. but if you decide not to remove them, keep all water away from transformers, relays and delicate meter movements. I saw one of my power transformers go up in smoke, even after what I felt was a thorough drying, baking and appropriate idle time. It was a high voltage transformer for a monitor scope, and even the slightest dampness in the insulating layers of the transformer were enough to cause its demise. If you want to skip the oven-baking step, the drying process can be accelerated by using an ordinary hair dryer for a short period and/or a muffin fan left blowing on the chassis overnight. If you do use dry heat, watch for dark colored parts (black plastic panels for instance) becoming too hot, too quickly.
More Backlip
Phil Salas AD5K offers this "happy mobiling" suggestion for hatchback owners: "So far, I've not
been able to find anyone who makes a 'true' hatchback vehicle antenna mount. Though you can
use something like the Comet RS-21 hatchback/trunklip mount on the side of the hatchback, you
can't use it on the top lip of the hatchback door. The reason behind this limitation lies in the fact
that the lip of the hatchback drops down below the vehicle's roof level, causing these types of mounts to hit the vehicle's roof before the hatchback door is fully open...at least this is the case with the Chevrolet Geo, the Toyota Tercel, and Ford Explorer hatchbacks that I've had experience with. To solve the problem, the vertical portion of the mount must to be moved, at least 1-1/4 inches, back from the hatchback lip.
I've had success in modifying a Comet RS-9 trunklip mount (which sells for about $12) in this application, by simply making a new lip mounting bracket. I cut off the RS-9's original mounting lip, and bolted the 'modified' unit to a new custom-made extension bracket with a #8 screw. For this new lip-mount-extension-bracket, I used a straight piece of steel from a standard 90 degree wood corner repair bracket (these corner brackets should be available at any well-stocked hardware store). I then bent one end of the bracket into a 'U' shape, so that it would fit over the hatchback lip on my particular vehicle. Next, I drilled and tapped the steel bracket for #6 setscrews. I've painted the whole bracket assembly black, and the final result looks pretty professional if I do say so myself! You'll have to adapt this idea to your own hardware and vehicle clearances, but Figure 2 should give you a rough idea of the approach that I used."
Good DXing
With the HF bands beginning to make a modest comeback, here's a tip from Tom Hart AD1B for ferreting out some of those often hard-to-find DX QSL addresses: "We all no doubt remember the thrill of receiving those first rare DX QSL cards in our mailboxes, but locating the correct address for the DX station, or his or her QSL manager, can be sometimes problematical. There is a way, however, to ease the problem if you make enough DX contacts to warrant the outlay. The GOLIST, published by John Shelton WB4RRK (address: The Heritage Group, P.O. Box 3071, Paris, TN 38242), compiles a monthly listing of DX stations and QSL routings for $3 per single issue or $30 per year for US mailing. They also have a computer disk version, a telephone BBS and an Internet site for faster updates; they can be reached by phone at: 901-641-0109 and tell them that you saw it in 73."
Murphy's Corollary: The ready availability of any electronic component will be inversely
proportional to the absolute need for that particular part.
Many thanks to the contributors who make this column worthwhile each month, their input is directly proportional to the needs of all of us for interesting ideas. This month, they include:
George Primavera WA2RCB
830 Park Drive
Cherry Hill, NJ 08002
Packet address: WA2RCB @ KE3CZ.#EPA.PA.USA.NA
Richmond B. Shreve Jr. W2EMU
POB 149
Bound Brook, NJ 08805-0149
Bill Turner W7TI
21607 56th. Avenue West
Mountlake Terrance, WA 98043
Phil Salas AD5X
1517 Creekside Drive
Richardson, TX 75081
Tom Hart AD1B
54 Hermaine Avenue
Dedham, MA 02026
Also, be sure to check out the Ham To Ham column's home page on the world wide web at: http://www.rrsta.com/hth. You can also pick up any back columns that you may have missed or misplaced at this site.
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.