Circle On Header Service Card

from audio to meter. The meter should indicate an output level when the LED lights. If the meter that you used pegs out with every transistor tested, you may have to install a 50k potentiometer in series with the meter to adjust sensitivity, it would be a good idea to check both NPN- and PNP-type transistors before continuing. To check a diode, simply connect the emitter and collector test leads to the diode and switch S2 to position h A good diode will light only 1 LED, while a shorted one will light both, Neither LED will light if the diode is open.

Going further

Experimenting with different types of transistors will quickly get you familiar with the test set. You can rapidly sort transistors for types and discard defective ones found in your junk box. You will be able to identify leads on unmarked transistors because the transistor will only oscillate when properly connected. I noticed that some horizontal output power transistors caused both LEDs to light during testing, even though they would oscillate and provide a good output on the meter. After checking the specifications for these transistors, I found that they were manufactured with an internal damping diode which made the transistor appear to be shorted!

You might want to consider adding a milliammeter in series with the collector test lead to measure the current of the transistor under test. To maintain the correct current polarity to the meter will require installing a bridge rectifier circuit in series with the collector and inserting the milliammeter in the center of the bridge. The bridge diodes will route the current in the same direction through the meter regardless of whether an NPN or PNP transistor is being tested. The diode bridge will cause an additional voltage drop of approximately 1.4 volts and this will affect the gain of the test set. In order to compensate for this, you may want to Increase the power supply voltage to 12 volts. The 555 timers can safely handle the voltage increase. Do not use a 12-volt supply unless you intend to add resistance of some type in the collector-emitter test circuitry to compensate. The higher voltage can cause the transistor, under test, to break down with reversed voltage (avalanche current) and both LEDs will light providing a false indication that the transistor is shorted.

Another alternative, to measure current, is to add a 100-ohm resistor in series with the collector lead and use the measured voltage drop across this resistor to calculate the current. For example, if the measured voltage across the resistor is L5 volts, then use Ohm's law to determine the current: I = E/R or 1,5 volts/100 ohms = .015 amp or 15 milliamps. The base current can also be calculated by measuring the voltage drop across the 10k resistor R7. The Hfe, or gain, of the transistor can be calculated by the formula Hfe = Ic/Ib where Ic equals collector current and lb equals base current.

I hope that this transistor/diode test set proves to be a valuable part of your test gear. If you find a modification that enhances it, Fd like to hear from you!0 73 Amateur Radio Today • May 1997 71

Rttv loop

Amateur Radio Teletype

Marc t. Leavey, M D., WA3AJR P, Of Box 473 Stevenson MD 21153

Well, about all that comes lo mind is that wonderful old song which goes, ''Though April showers may come your way / ihey bring the flowers lhal bloom in May/' While we have had our share of precipitation here in the mid-Atlantic states, blooming here at WA3AJR arc your questions, and what questions they arc! This month brings a pack of real problems.

I'll start with one from Wayne Grove K9SLQ, who writes that he recently uncovered his Model 28 in the garage, picked up a tape recorder and TU, fired the sucker up and enjoyed the sounds again from, the oT 28, Well, his question is, "Where can I find some of the old PIX we used to send in file form? 1 combed your articles but could not find any mention of the P1X in the 'Good Or Days'."

Well, Wayne, several years ago I ran an entire feature on TTY pictures, some of them quite complicated. In fact, it seems to me thai for some years there was a competition on the air to see who could come up with the most creative picture. Some of them were very creative, indeed! Unfortunately, with Lhe onslaught of computer terminals, many of which sported a different line length than teleprinters, and few of which could back scroll to view transmitted pictures, it seems to have gone out of vogue. I have asked several times here in the column for submissions, and have received none, So, unless you happen to run across someone with a good collection of old paper tapes, 1 am afraid that this may well be one area where the computer is just not as much fun as an old mechanical printer

With the recent demise of AEA, as reported in this column a bit ago, we are beginning to see more unanswered questions about some of their products.

Such a question comes from Chris Cieslak AA9HDT who writes: "I've been using RTTY now since last summer, starting with lhe HamComm circuit and recently graduating to a used PK-232 bought at the iocal hamfest, (The first time I used it after replacing ^ few parts and cleaning ii up was the RTTY Roundup—talk about trial by fire!) I have one question: Do you know of any home-hrewable scope-style tuning circuits for the PK-232, which has outputs on the back for a scope ? The timing indicator on the front is nice, but 1 ve always liked the cross displayed on a scope. 1 know 1 could use an old hamfest scope, but my limited shack space and sense of aesthetics requires something a bit smaller.7'

Well, Chris, Vm afraid that the short answer is "no." I have seen a few circuits in the past for LED-type display boards, but these were years ago, and relatively clumsy by today's standards. I would not be surprised. though, if some reader of this column has not already put together such a device. If 1 hear about it, I'll print it for all to benefit.

Another AHA user, Ron Modeste N3AHD, bought an AEA CP-1 at a local hamfest, and is looking for a way to copy RTTY or CW with an IBM-style computer with this device, designed for the C-64, Well, Ron, while I have printed a lot on the CP-l over the years, never has anyone written with a eonncc-lion scheme lor lhe PC, Somehow, ] feel this is possible, hut not having access to a CP-l nor full documentation, 1 am loath to suggest a way. If any of our readers have done it, I'm sure we will both hear about it, real soon!

Not satisfied with one question, Chris Cieslak AA9HD adds:

''Oh, OK. One more question. Have you heard anything about using the ICOM 728 for RTTY? I've been using it full power for a while and while it s gotten quite warm, it wasn't hot enough to burn or anything. The manual mentions nothing pro or con on keydown RTTY. QST says die radio was barely warm after several minutes of keydown full power, but what about repeated use ? I love RTTY and operate it more than anything else (except maybe S3TV) so Td hate to have to turn the power down/'

While I have not heard any specific information about the ICOM 728, in general, most modern rigs should not be run wide open, key down, for any length of time. I hear you about getting only barely warm, but that's on the outside. Who knows how warm it is at the component level? I'd play it a bit safer and back the power down a notch. After all, in the scheme of things it may only be □ decibel or so difference on the air, versus a decade or so life of the equipment. I'm open, of course, for comments on this one, as well!

Ford A. Peterson N0OQW writes that he is looking for software to run his HAL Communications ST-6000, He indicates that an old program, HAMRTTY, worked well, whereas the newer Hamcomra program does not compare, fie wonders which of the newer crop can use all of the features of the ST-6000.

Well, Ford, my experience with HAL devices ended with the ST-6, I'm afraid, [...Why are you afraid, Dave?] I do recall that the ST-6000 had some gizzies that took it head and shoulders above other demodulators of its time, but although I looked through some of the packages in the RTTY Loop Software Collection, 1 did not see any which specifically mentioned the ST-6000. 1 would be interested in any reader's experience with this TU in modern systems,

Of course, things can get too modern! A while back we were talking about using various sound cards on RTTY, and Tom Petruzzelli WA2ANG is "still looking for any programs that use the Soundblaster card lor sending or receiving RTTY and/ or CW, Do you know of any software either commercial, freeware or shareware?"

Well, Tom, while I was not able to find any RTTY program for the Soundblaster card, 1 have located a program called SSTVBL.ZIP. which allows slow scan television with a computer, Quick-Cam camera, and Soundblaster card. I've also found a program called SBPMORSE.ZIP which is a xMorse code reader using the microphone input of Lhe Soundblaster card, I don't know if these will run with"compatible" sound cards, as they both list the Soundblaster by name as the audio card of choice. 1 will be putting both of these programs onto a disk in the RTTY Loop Software Collection. See details below lor how you can obtain any or all of these programs lor yourself.

While some of the folks mentioned above have been trying to get C-64 hardware, like the CP-l, to run with PCs, Jerry Olson WB0AAC says that he is looking for software to interface his Commodore C-64 computer with Lhe Kantronics UTU demodulator, for running RTTY, AMTOR, or CW. Again, I can't see why ii shouldn't work, if the connections car be put together. Anybody?

I have mentioned the RTTY Loop Software Collection above. The listing of this collection, over fifteen disks of RTTY programs for DOS and Windows operating systems, is detailed on the RTTY Loop Home Page, on the Web at: ajr/rtty/ or you may obtain it by sending a self-addressed, stamped envelope to the above address, Next month, 1 have a new offering from overseas, which represents a unique merger of two ends of this cra/y hobby, intrigued? Don't miss next month's RTTY Loopl

Rduertisers' Indem

R.S.f page

351 Absolute Value Sysiems ... 43

66 Advanced Battery Systems .. 81

194 All Electronics

Corporation 16

57 Antennas West 1

336 Antennas West 15

116 Antennas West 23

132 Antennas West 25

332 Antennas West 31

340 Antennas West 4t

5 Antennas West , 43

135 Antennas West 45

• Avcom of Virginia 39

41 Barry Electronics Corp 43

163 Bisme Computers 55

168 Buckmasier Publishing 47

56 Suckmasler Publishing 49

222 Byers Chassis Kits 28

186 Coaxial Dynamics 15

99 Communication Concepts 39 10 Corrmjricaûûns Specialists. 33 276 ComputerA>dedTechnology. 3/

268 Computer Automation

Technology 61

166 Cubex 43

* Dayton Hamvention 29

13 Doppler Systems „ 24

114 Eh H. Yost 25

• Gap Antennas CV3

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