Ham To Ham #7 - April 1996
73's Ham To Ham column
c/o Dave Miller, NZ9E
7462 Lawler Avenue
Niles, IL 60714-3108
In the December 1995 Ham To Ham column I wrote about using an IR detector diode across the mic input of a high gain audio amplifier in order to test the remote's operation - at least to determine if it's outputting pulses. Klaus Wolter, N8NXF, of Ann Arbor, Michigan notes that another way to "view" IR LED's is via a CCD television camera. Apparently, some CCD cameras have enough response in the infrared region to "see" these remotes pulsing when aimed at the camera's lens. Vidicon cameras probably won't. On the other hand, F.A. Bartlett, W6OWP, and Erich Kern wrote in saying that all you really need to do is to hold the IR remote next to the tuning section of any AM broadcast receiver to "hear" the pulses. They're right, because these hand-held IR remotes put out a fair amount of digital pollution, they'll come over an AM receiver very nicely, proving that there is indeed room for too much engineering sometimes! For testing the operation of IR headphones and microphones, the IR detector/audio amp idea that I proposed is still perhaps the best way, but there are always other alternatives...which brings me to the purpose of this column...to provide a forum for your own ideas, even if they may be "different". A good initial response has been received, but I still need many more tips, ideas, suggestions and better ways of doing things from all 73 readers. Don't worry about your writing skills, just include as much detail as you can and I'll put it together in the style of the column. Let's hear from you!
This month we begin a series of tips offered by Richard Measures, AG6K, of Somis, California. Rich as done a tremendous amount of reseach into VHF parasitic oscillation suppression in amateur HF linear amplifiers, as well as fathering many practical servicing tips for some of the current amateur transceivers and accessories. With Rich's permission, I've condensed some of his best suggestions into the column's format, and over the coming months, I'll include one of his tips in each column...be sure to watch for them.
One inoperative meter cure
Richard Measures, AG6K, of Somis, California, explains how an inoperative meter may not necessarily be bad, just in need of a good overhauling. With time, humidity and the natural corrosive effects of the atmoshpere, the meter used in the Heath SB-220 linear amplifier can appear to be unusable. But as in other areas of life, appearances can often be deceptive. The meter Heath used in the SB-220 is not unlike the meters used in many other pieces of ham gear, so the techniques I'll explain here aren't just for SB-220 owners by any means. Here's the reason: many meters are assembled using different types of metals for the various meter parts. These parts, which are then expected to conduct current to the meter's armature, are fastened together using machine screws at the joining points that act as the electrical conductors within the meter. As previously mentioned, time and the effects of humidity and pollutants in the air, can result in electrolysis occurring at the junctions of these dissimilar metals - a perfectly natural phenomenon - but definitely not desirable within our meters! The increased resistance at these junctions can cause an intermittent or open connection at various points between its rear terminal and the meter's movement.
The problem can very often be solved by simply carefully prying off the plastic meter face cover, even more carefully removing the scale - usually held in place with two tiny screws - and then applying small dabs of conductive paint (such as GC Electronics Silver Print) to all of the dissimilar junctions that carry current to the meter's armature winding. The conductive paint can be applied with a straightened-out paper clip; it can also be thinned with ordinary acetone to facilitate penetration into any narrow areas between parts. Be careful not to get it onto any part that you don't want to conduct electricity however! It should also be allowed to thoroughly dry before any reassembly takes place, since the undried fumes could cause problems of their own.
Be very careful when working inside one these little meters, a wrong slip could spell the end for it, but at least give it a try...chances are better than even that you'll be successful, which are surely more than if you had done nothing at all.
Richard L. Measures, AG6K
6455 La Cumbre Road
Somis, CA 93066
Moderator's note: The silver conductive paint that Rich refers to can often be obtained from local electronic suppliers or by mail-order from the larger supply houses. MCM Electronics (1-800-543-4330) stocks their catalog #21-1555 Silver Conductive Pen.
An "automatic" antenna disconnect suggestion
If you take advantage of a "master" station-power on/off switch, as do I, to disconnect all power from your station equipment to prevent "unauthorized little fingers" from turning on your ham gear, then here's an extension of that protection for your antenna circuit as well.
Disconnecting your outdoor antenna from your transceiver, when the equipment is not in use, is always a worthwhile safety precaution, in the event of a nearby lightning strike or other static buildup that might occur. It can be made "automatic" very easily, by simply installing a coil-actuated antenna relay in the path between your antenna's transmission line, and the station transceiver. Coil-actuated antenna relays used to be quite common in the days of separate transmitter/receiver combinations, to switch the antenna between those two units, before the current trend of transcievers with built-in T/R (transmit/receive) switching. I've often seen them at hamfests, amid other "ancient gear", and at very resaonable prices. If the T/R relay has a 120 volt AC coil, you're all set, just put a cord and AC plug on it, and plug it into your "master" AC strip. If it has a 12 volt DC coil - as might have been used in a mobile set-up - then wire it to your station 12 volt DC power supply's output, as long as the 12 volt power supply is switched off with the "master" switch.
Make sure that the relay's contacts will handle your normal output power - most will - and clean the contacts with a thin strip of 3" x 5" index-file-card material, soaked in contact cleaner, via the relay's contact access port. The contact access port is usually covered with a removable cover-plug, or in some cases, the whole cover of the relay itself may have to be removed. It's not usually a very difficult job. Don't file the contacts unless you've had lots of experience with relay maintenance though, they're usually silver (plated or solid) and you can do more harm than good by filing them...use only a paper file card, not a file! A special diamond-dust relay burnishing tool is normally used, and instructions on its use, if filing is absolutely necessary.
Now cable the relay in series with your incoming antenna coax, so that your antenna system will be connected to your transceiver's output when the relay is "pulled-up". Install a "shorted" coax connector into the left-over fitting, so that the antenna's transmission line is shorted when relay is relaxed - when the station AC power is "off". Finally, ground the body of the relay to a reliable earth-ground to safely "bleed" any static build-up away to the earth.
With your transceiver's antenna lead automatically disconnected, and the antenna itself shorted, you can sleep a bit more comfortably when Spring thunderstorms approach. This won't completely protect your equipment from a direct hit - very little will - but it does help to protect your investment from nearby lightning hits and static build-up damage.
DE Dave, NZ9E.
Dig-out your mobile vertical!
Winter is hopefully coming to and end, but here's a tip from William Thim, N1QVQ, of Broad Brook, Connecticut, that may still have application this season for some. While you're in the process of cleaning that snow and ice off of your car windows, don't forget to dig-out your mobile antenna! A build-up of snow and ice around the base of your VHF or UHF mobile whip antenna can significantly raise your SWR, even to point of forcing your transmitter to cut back on its power output. Check it with a good SWR bridge and you'll see what I mean. 2" to 3" of snow built-up around the lower active portion of the antenna will often result in a very noticable SWR change.
William Thim, Jr., N1QVQ
50 Miller Road
Broad Brook, CT 06016-9676
Moderator's note - Bill brings up a good point, thought the bottom part of a 1/4-wave vertical is the high-current, low-impedance end of the antenna, depending upon the amount of snow and ice and the operating frequency involved, the tuning of the antenna - and its losses - can be altered quite a bit. It's something we may not always think of when we're not hitting the repeater quite as well as we used to!
An all-purpose probing-tool from the Far East!
Herb Foster, AD4UA of Melbourne, Florida offers this suggestion: Whenever I'm working on a piece of electronic equipment, I like to have an insulated tool in one hand to point, probe or gently tap a component or connection that might be suspect. This one is effective and, best of all, free!
Most Chinese restaurants give away wooden, bamboo chopsticks to their customers, to kind of get you into the "spirit" of eating-out oriental style. So the next time that you have the urge to take-in one of these restaurants, save the chopsticks for your work-bench tool inventory. When you get back home, wash them up and carve one end of each into a point, a flat-blade screwdriver or even a hex-type of core-adjusting tool, and keep them handy on your bench. You can use them to poke around a crowded circuit board without fear of shorting anything out, or even use one to prop something open, if your transceiver is built into "layers" as so many are these days. And if your neck starts to itch, you can even use it to reach behind and scratch!
All that you need do to obtain a supply of your own is to develop a liking for Chinese food, then take the wife and kids out for dinner. Even if you don't care to try manipulating the chopsticks with your meal, that's okay too, they'll loan you a fork and still let you keep the chopsticks...and you can't beat the fortune cookie at meal's end either!
Herb Foster, AD4UA
3020 Pennsylvania Avenue
Melbourne, FL 32904-9063
Moderator's note: Good idea Herb, bamboo keeps it's shape better that many other woods, so whatever type of tip you might put on the end, chances are it will last longer than in pine or other soft woods. By the way, if the fortune cookie at the end of the meal says something like: "Avoid anything electronic today", better listen to it, you never know!
Airing taped-telephone ham bulletins
Here are several suggestions from Mike Schroeder, N0ALJ, of Rogers, Arkansas for those of you who might be contemplating handing the airing of telephone-line originated amateur radio bulletin services for use on your local repeater's net-nite get-together. I've been assigned to air the bulletin services - such as RAIN and Newsline - on our Monday night repeater net on 146.76 Mhz., and as such, I felt that I needed the best quality telephone audio possible, plus an easy-to-install record/playback system. Instead of a simple telephone inductive pick-up coil, the Radio Shack #43-228 does a much better job, and having a built-in speaker, it allows me to monitor what's being laid down on tape. I also use a multi-memory phone to make dialing easier and so that I can program-in alternate numbers, just in case the ones I normally use are busy.
Another interesting method I've found to make quality recordings is to dial up the service you want to record on a cordless phone, then use a scanner to pick-up the radio frequency of your phone, and make a recording from the external speaker jack of that scanner.
As far as playback of the tapes over-the-air on net-night, if you want something simple, you might try an inductive pick-up coil backwards - such as the RS #44-533 - if you have a dynamic or magnetic type of mic on your 2-meter transceiver. In other words, feed the tape machine's earphone/speaker audio output into the inductive pick-up, and place the coil over your mic. This won't work on the new electret-condenser type microphones, but in that case, the easy to build interface box shown in Figure 1 can be used.
Using an inexpensive digital timer (such as the Radio Shack #63-884) that's started when the tape is started will give you an elapsed time indicator, so that station ID's can be inserted at the proper times. The tape can be paused for the ID by simply having an SPST toggle switch on a cord, plugged into the tape machine's remote stop/start jack. If fact, all of these functions can be integrated into the one central control box - recorder interface with its mic/tape switch, remote tape stop/start switch, transmitter PTT switch and a small digital timer - all equipped with the correct plugs to mate with your specific equipment. On net night then, it's almost an automatic few-second-set-up to get things going correctly, instead of a Murphy-prone chore!
Mike Schroeder, N0ALJ
402 N. 38th. Place
Rogers, AR 72756
Moderator's notes: Good tips, Mike. Building everything inside of a metal box and using shielded cabling will help to reduce the possibility of RFI problems during the on-the-air phase of the operation. If you still have problems, try putting small ferrite beads on all of the input/output leads, and/or .001uF disc capacitors from the offending lead to ground. At 2-meters, sometimes a lead will inadvertantly end up being either 19" or 38" long, acting as a resonant pick-up antenna for your own signal! Check for that too.
For your files
Here are some good suggestions from Joel Masur, AA5YA, of DeLand, Florida, for working aluminum sheet stock. What follows is an idea that you might want to try if you've ever had difficulty "squaring up" aluminum sheet stock for panels, etc. Try to locate an old time lead body file, mine is a New Britain #285; an auto parts store or older auto body shop might be a good place to start. Mount it on a husky wooden handle, so that it resembles a flattened wooden block plane. The half-moon shaped teeth in a file like this will eat-away at the soft aluminum very nicely, without the normal tooth-clog problem we're all familiar with in finer-tooth files.
Additionally, you might try Forstner wooden bit and power auger files for getting into the corners of the square or rectangular cut-outs needed for snap-in switches, etc. The ones I have are 7" long, 1/8" thick and 7/16" at the widest part. They're shaped something like a diamond that's been stretched-out to the 7" length but with a 1/4" wide by 1-1/2" long connection strip. One end of it has teeth on the flat side and none on the edges, the other end is exactly opposite...no teeth on the flat side but teeth on the edges.
Now that you have the tools, what about the stock? Free is always nice, and here's an approach you might want to try. Make friends with the public works department foreman in your town and see if he has any salvaged road signs that he'd just as soon get rid of. They can make great electronics panels if they're not too badly damaged. Leave any decals on until you've cut and finished the material for the project you're working on for protection of the under-finish.
Octagonal "stop" signs make nice 2 meter ground planes for a mag-mount antenna, providing they're made of steel. Other steel traffic control signs can also be used for the same purpose if they're sized about right (roughly 40" by 40").
If the public works foreman has any outdated aluminum trafic control counter boxes taking up space, latch onto them; They're the boxes you'll sometimes see placed at the side of the road, chained to a tree, with a long rubber tube comming out of them and onto the roadway. They count the number of cars using a particular road over a period of a few days, but the discarded ones also make great boxes for outdoor tuning units, power supplies, or even an entire mountain-topping QRP station! The air hose hole can serve as an input/output access. Just be sure to go through the right channels when helping them to get rid of their obsolete signs and boxes, you don't want to be operating portable from the police department's holding cell!
Joel F. Masur, AA5YA
1465 Chris Avenue
DeLand, FL 32724-6187
Moderator's note: If the auto body shops you check with don't have the files that Joel is referring to, ask them where they purchase their supplies and try directly. You might also check with the W.W. Grainger outlet nearest you, as well as any other contractor's supply houses in your area.
A "quick tip" for testing transistors
Peter Albright, AA2AD, of Lakewood, New York, offers this suggestion for quickly testing out-of-
circuit transistors. Here's an easy method of using a multimeter's "ohms" scale to reliably test
transistors. The very few minor limitations are as follows:
1. It works best with an analog (needle style), rather than a digital meter.
2. It should really only be relied upon when the transistor has been removed from circuit.
3. The test works on bipolar transistors only, not on FETs, SCRs, etc.
4. It doesn't yield any information on a transistor's gain or "beta".
The limitations, in my opinion, are more than offset by these advantages:
1. The test is very fast and requires no specialized equipment.
2. You will get no false "defective" results.
3. The only false "good" result might be from a thermally-sensitive transistor, ie., if the
transistor only shows a defect under the stress of heat during actual operation.
4. It can often be used as a first step in identifying lead configuration.
Here's the theory: There are two types of semiconductor material, "P" type and "N" type. A
junction diode, such as a silicon power diode, consists of one layer of "P" material mated-against
one layer of "N" material, and this junction conducts current in one direction only.
Bipolar transistors, on the other hand, always consist of three alternating layers of these three
materials - either "PNP" or "NPN" - with a wire connected to each of those three layers. To an
ohmmeter, which has only two test leads, the transistor looks like two diodes, either back-to-
back, or face-to-face. This concept alone takes a lot of the mystery out of transistors.
Regardless of which type of transistor is being tested, the wire to the center layer is the base,
while the two outside layers are the emitter and the collector. So the configurations, when drawn
as simply diodes, are:
PNP NPN
either ----->|-----|<----- or -----|<----->|-----
| | | | | |
E B C E B C
In practice, it's really easy to test a diode with an ohmmeter. Set the meter to the R times 1K
range. Measure the resistance, first in one direction and then in the other, by reversing the
ohmmeter's test probes. Silicon diodes will measure virtually infinite resistance when the positive probe is connected to the diode's cathode (usually marked by a band). Conversely, they'll measure some continuity when the positive probe is connected to the anode. Note that not all multimeters apply a positive voltage to the red meter lead, you'll have to test your own meter with a known good diode first, then mark the meter as to which test lead is actually outputting a positive voltage. It need only be done once. Germanium and selenium diodes on the other hand, which are point-contact diodes, rather than junction diodes, may show some continuity in both directions, but the resistance in one direction, will always be much higher than the other, if the device is good.
If you're still with me, you've probably already figured out how to test a transistor with an
ohmmeter, thinking of it in terms of two diodes. Here's the procedure, in step-by-step format:
1. ALWAYS turn the equipment off, unplug it or remove the battery, and discharge any filter
capacitors - usually identified as the physically larger capacitors.
2. Completely remove the suspected bad transistor by carefully unsoldering it from the circuit.
3. Set your ohmmeter to the R times 1K scale or higher. This limits the testing current,
protecting
the transistor from damage. Don't use the very low ranges on your meter for these tests.
4. Connect either lead of your ohmmeter to what you believe to be the base of the transistor.
5. Measure the resistance to each of the other two leads. The reading should be the same for
both leads: either nearly infinite (open) or finite (some continuity).
6. Now switch probes, that is, connect the other probe tip to the base.
7. With the probes now reversed, measure the resistance to each of the leads once again.
The reading should again be the same for both leads.
a.) If your result the first time around was "infinite", then you should now see some
continuity between base and emitter as well as between base and collector.
b.) If your first round results showed "continuity", then your measurement now should
now be nearly "infinite" resistance (open) to both emitter and collector.
8. If you get some result other than these, then assume that the transistor is defective (or
perhaps you've misidentified the emitter, base and collector leads).
Notes:
a.) As with germanium diodes, germanium transistors may show some continuity in both
directions, but there will be a distinct difference in the resistance when you reverse the
probes. You probably won't find many germanium transistors in equipment less than twenty
years old, but you will find germanium diodes in more recent gear.
b.) If the transistor is bolted to a metal heat sink and has only two leads coming out of it, then
the bolt tab or threaded stud will be the third connection. Bolt tabs and studs are always the
collector.
c.) If you don't know the lead configuration of a device, you can use this technique, along with
trial and error, to at least identify the base lead, provided the device isn't defective.
If you REALLY understand this technique, it can save a lot of time and trouble, as well as taking
some of the mystery out of transistors and solid-state electronic troubleshooting in general.
Peter Albright, AA2AD
28 E. Summit Street
Lakewood, NY 14750
Moderators Note: Peter's suggestion is a good one to remember, it's a good "quick test". It might
pay to clip this out and post it near your workbench, so that it's handy the next time you need it.
It would also pay to practice on a few good transistors, now, just to get a "feel" for what he's
saying and to overcome any reluctance that you might have to solid-state troubleshooting.
Hands-on learning is always worthwhile, after all, you can't do much harm...and it's good hand-
to-eye coordination practice!
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.