In This Issue: Portland Marathon Meeting Info Scouts use Packet Construction Article |
Door Prize Winner August Meeting BBC..end of an era Psycho Appliances |
PARC Frequencies Voice: 146.840 –600 MHz 146.940 –600 MHz Packet 147.180 +600 MHz (repeater) 144.910 (W7LT PARC Node) |
ARES MEETING: Thursday, Sept 27th at Fire Station
2 4800 NE 122nd at 7PM. All hams are invited to attend!
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By Lea AL7W Psssst!!!! Wanna know one of the best-kept secrets of ham radio? The digital modes don’t cost an arm and a leg to use, when you have the right stuff on hand, and most of us have Pentium 100 or better computers, and radios that are stable enough to use these modes.. I always associated the digital modes with boat-anchor Teletype machines or Robot interfaces and quite a bit of money. Getting on PSK31 or SSTV or RTTY only requires an inexpensive interface and easily downloaded sound card software written for it. This software is generally available as freeware or inexpensive shareware. You will, of course, need to hold at least a General-class license to go on the air with most of what is outlined here.
In theory, one could connect his sound card directly to his radio, either through the accessory jack on the back or through the mike and headphone jacks. The only thing that would need anything special would be the means of actuating the PTT line of the radio (see fig. 1). Even that can be finessed by using VOX, but it’s not the most reliable. Most simple interfaces for which I’ve seen diagrams also include a simple adjustable attenuator for each of the audio lines involved. Typically, this consists of a pot (at least 10K) and a 1:1 isolation transformer for the individual circuit. The particular wiring depends on which direction the signal’s going (see the diagram for the whole unit, in fig. 2). I built mine for a probable total expenditure of about $15, buying most of the parts at Radio Shack.
Figure 1: A simple PTT circuit (not recommended) The Circuit Figure 2 shows a very good way to hook up the PTT switching interface, using an optoisolator to completely separate the ground buses of the computer and the radio. I am deliberately not including instructions on how to hook it up to your radio, because different ones do things differently. A quick perusal of your radio’s user manual should give you the means to connect up. |
I prefer to connect to the accessory jack on the back of my IC-735, and those connections are model-specific. With the exception of the Optoisolator (which can be gotten at Norvac Electronics), all the parts can be gotten off the shelf from Radio Shack (their part numbers are included). There are 3 parts to the circuit, and the first 2 are virtually identical, except for how they’re wired up. We need to get audio from the Line-Out (or speaker) jack on your sound card to the input of your radio (either mike or accessory jack, your choice). We also need to move signals in the other direction, either from the accessory jack or the headphone jack of your radio to the Line-In or mike jacks of your sound card. If you’re using a laptop computer for this, you’ll be using the latter connection points in both cases, since there is no line-in or -out point on most laptops. The third part of the circuit is, of course, the Push-To-Talk switching done by the serial port on the computer. The 2 1N914 diodes, D1 and D2, are put in to capture both the RTS and DTR lines of the serial ports, without them feeding back to each other. This is to make less critical the assignment in software (they can default to either or both) of the switching line. R3, the 2.2K resistor, is there for current limitation.
Figure 2: The complete interface
Parts List
D1, D2 - 1N914 diodes (RS276-1122, pk. of 10)
D3 – 1N4001 diode (optional, used with Q1)
J1 - DB9F serial connector (with cable)
P1, P2 - 3-circuit 1/8-inch phone plugs with
cables (see text)
Q1 - 2N2222A transistor (optional) (RS 276-1617)
R1, R2 - 10K PC-mount pot (RS 271-282)
R3 – 2.2k resistor (RS 271-1325)
T1, T2 - 600-Ohm 1:1 isolation transformers (RS
273-1374)
U1 – NTE-3083 (available at Norvac Electronics;
a socket is advised).
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Going Digital on the Cheap (continued) Construction I built my interface on a piece of Radio Shack 276-148 perfboard. Since we’re working entirely at DC and audio frequencies, things are relatively uncritical as to layout, as long as there are no solder bridges between critical pieces. We want to not make common ground connections on the computer sides of the 2 isolation transformers, T1 and T2. I also used pc-mount pots on my interface. These would allow the unit to be housed in an Altoids box, using double-stick foam tape to mount the board. If you connect the cables directly to the board, you’ll want to employ some form of strain-relief where they exit the box. You’ll also want to label them for their appropriate functions. A circuit board is being prepared for members’ use.
Figure 3: Circuit board pattern
Figure 4: Parts Placement Software This is another area where personal choice runs rampant. There are several good packages of software for PSK31 that are available for download, free of charge. My initial choice, based on the recommendation of Steve Ford, WB8IMY (now the Editor in Chief of QST), was DigiPan, which allows panoramic display of the passband of the IF of your receiver (and usually encompasses the PSK31 activity on that particular band) |
You can also see when someone’s running a really lousy signal, because you’ll see more than 2 parallel lines for that guy’s signal, indicating splatter. Tuning in a signal using DigiPan is easy, because you use your mouse to drop your cursor in the space between the parallel lines in the waterfall display. Since the signal is only 31.5 Hz. wide, a large number of signals can be accommodated in the 2.4 kHz. passband of most people’s SSB receivers. The current release is 1.6d, and it will be posted on the club’s website for download. (as soon as we can).
Figure 4: A typical PSK31 Display (from WM2U’s website) I have also used my interface for RTTY and SSTV, and there are a couple of downloadable freeware packages. of Japanese origin, that I’m using for these modes. These are MMSSTV (reviewed in the August QST by WB8IMY) and MMRTTY. Both are available for download from www.geocities.com/mmhamsoft/mmsstv/index.htm, or from the club website. |
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Going Digital on the Cheap (continued) Adjustment Once you have your unit constructed, it is pretty easy to adjust it for proper use in PSK31 (which will also set it up properly for the other digital modes). The following procedure for setting it up assumes that you’re using DigiPan. For receiving, R1 should be tweaked up to the point where the background changes from blue to yellow, showing background noise for the bandwidth of your IF filter (in my case, about 2.4 kHz, out of a display width of 3 or 4 kHz, depending on the resolution of your screen). If it turns yellow all the way across, you’re overdriving your sound card, or there are a lot of strong signals about. For transmission, you are trying to get a clean sine wave from your sound card to the audio input of your transmitter. In stubborn cases, you may need to use an oscilloscope to set the output level from your computer (especially from a laptop). R2 is what you are using to adjust the audio level to the transmitter. You want to go into transmit mode (preferably into a dummy load), with the transmitters metering set to ALC. You want the highest setting that doesn’t deflect the meter when transmitting (have your software call CQ and monitor the ALC). Monitoring power output should show a little bit of deflection, but it’s nominal. You want to shoot for IMD readings on the other end of less than -20 dB. If you’re at all nervous about getting it right, get hold of me. I (or someone else on the air) can give you a fair assessment of the quality of your signal. Great gobs of output power are generally unnecessary with PSK31: people generally throttle their signals way back on that mode; claimed power levels of 20 or 30 watts are quite common. It does pull the weak ones out: people do get copy on signals that only put ghost traces in the waterfall display that aren’t audible at all. I did try using this lashup in the North American RTTY QSO Party, at the end of July, but it turns out that power does matter more on RTTY than in PSK31. I did get some contacts on 20 meters, but they were sporadic, and there was at least one local station (K7ZUM) that didn’t hear me (or maybe Ken was ignoring me, I don’t know).
Conclusions I’ve been a ham for 40 years. In the past 10 or 15 years, I’ve not spent a whole lot of time on the air. It would be safe to say that in most of that time, I’ve signed W7KYC or W7LT more than I have my own callsign. Moving to the digital modes has started to tip the balance in the other direction. |
The thing of it is, had I realized this 2½ years ago, I’d have been one of the first people in town on PSK; instead of a Johnny-Come-Lately. For the first time in a long time, I’m enjoying ham radio again. -AL7W
Bibliography Ford, S., WB8IMY: "PSK31-Has RTTY’s Replacement Arrived?" QST, May, 1999, page 41. Ford, S., WB8IMY: "PSK31 2000" QST, May,2000, page 42. Ford, S., WB8IMY: "MMSSTV Version 1.01" QST, August 2001, Short Takes, page 61. Kruis, R., K8CAV, "Clean Up Your PSK31 Signal" QST February, 2001, Technical Correspondence, page 88. Kruis, R., K8CAV, "Revisiting ‘Clean Up Your PSK31 Signal’" QST, April, 2001, Technical Correspondence, page 83.
Editor’s Note: I did a board layout for this project, and am planning to etch several copies of them for the club. They will be available at the regular meeting on a limited basis. For the ease of board layout and etching, I omitted the holes for all but the necessary pins on the 9 pin RS-232 connector. It is intended that you cut the unused pins off before soldering the connector to the board. If you prefer, a cable may be substituted for the connector, soldering the cable connections directly to the board and supplying a strain relief for the cable. It is also believed (but not tested by the time this went to press) that this same interface will work with 1200 and 9600 sound card based packet applications on Pentium 166 and above PC’s. This could become a clean sweep on entering the digital communications on a whole bunch of fronts! It is my intent also to provide on a limited basis CD’s containing the software mentioned in this article, as well as a few others that are free, or provided on a shareware basis by the authors. If you have an idea that would make a good construction, or technical project, please drop me a line: kc7gfx@arrl.net Wanted: Articles for the sPARC gap. Any size will do, pictures (digital or analog) are a nice touch. Send them along to me, Ed Burress, kc7gfx@arrl.net |
Bert Younglove, WA7AXO was the winner of the door prize at the August club meeting. Bert took home our first (well, our first in quite awhile) prize of a Compaq laptop computer. Bert plans to use the laptop for packet radio and teaching at the ARES meetings. Door prizes are planned for each of the meetings. Prizes may be hardware, gift certificates, kits, accessories, or the ever favorite gag gift. Each person signing the roster at the meeting is eligible for the door prize. Bring a friend, you each get a chance!
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Scott Etlinger, KC7ZUH - American Red Cross
Scott Etlinger (above, left) from the American Red Cross spoke at the September meeting about the role of the Red Cross during normal, and emergency situations. He discussed preparedness for Earthquakes, wind and ice storms, and other natural and man made disasters. I think that all of us associate the Red Cross with blood drives, handing out blankets and establishing shelters during floods, mudslides, tornadoes, and hurricanes, but the Red Cross does much more than that on a daily basis. Did you know that they respond to single dwelling house fires? How many of us knew that they provide vouchers for motel rooms, hand out bedding and clothing for families who have lost everything in a fire? They also maintain a fleet of food service vehicles to provide food and liquids for fire fighters that are called out on three alarm fires. They were present during the Portland flood, providing hot coffee and food for the folks filling and placing sand bags down at the waterfront district. The Red Cross is always looking for more volunteers to help establish a network of ham operators for their emergency operations. Volunteers get free (or greatly reduced cost) training on first aid and CPR, and provide a valuable service to the community in times of need. If you’re interested in becoming a volunteer, give Scott a call at (503) 280-0205. Our many thanks to Scott. for a great presentation, and for the donation of coffee for the coffee stops. |
On June 30th, 2001, the BBC discontinued its World Radio Service broadcasts to North America and most of the Pacific. As an early short-wave listener, this used to be one of my favorite stations, listening to it on a surplus BC-348 receiver out of a W.W.II bomber. A reflection of the changing times, the BBC is modernizing its business model and now relying on it’s Internet broadcast feature to reach our portion of the globe. The reasons are simple, the cost of internet broadcast is much lower than continuing to maintain and operate it’s high powered transmitter, provides much better audio quality, free from fading and static, and more people in our region have internet connected computers than short-wave receivers. Another service, Worldspace utilizes the digital satellite radio broadcast method. I’ve listened to the BBC over a DSL line, and I have to admit the quality of the audio is good, but somehow lacking the magic that kept it alive since my childhood. Modern technology is a wonderful thing……….right up until the phone lines go down.
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The following article is from the September 2001 issue of "Highways", a publication of the Good Sam Club. The original article was in their Tech Topics column and titled "Psycho Appliances". I enjoyed the article in the April issue on the Good Sam chapter in Arkansas that is made up of ham radio operators. I’ve been a licensed ham since the mid-1950’s and am a member of the Good Sam amateur radio chapter here in Texas. I have a recurring problem that has me really puzzled, and with which I have had no real help from the manufacturer. I own a 1998 Chateau travel trailer that I purchased new and that has a Duo-Therm air conditioner and thermostat. The thermostat and the control panel are "solid state." When operating my amateur radio transmitter from the trailer, the air-conditioner compressor will engage, regardless of the temperature setting of the thermostat. I have talked with other RVers with similar problems. One even told me that the automatic steps on his motor home would extend or retrace during his radio sessions. Most, however, seem to have the same or similar problem with their refrigerator controls. Early on, I placed several calls to the manufacturer of the air conditioner, and was told what could be done to solve the problem, and that there were no alternative control devices available. One person I spoke with sent me a relay with no instructions on its installation or purpose. I have done extensive troubleshooting myself with very poor results. The most frustrating part of the matter is the apparent lack of interest in helping from those who presumably are in the best position to do so. I would appreciate your help. Fred Zimring, Richardson, Texas.
Consider yourself lucky, Fred. There have been cases where the windshield wipers activate on their own or the engine stalls because the radio-frequency emissions make the engine computer suddenly change the air/fuel mixture. You only had to put up with a cold interior and melted ice cream. The first step in diagnosing this problem is to double check the ham radio antenna system radiating element, as well as the necessary metal ground plane below it, The antenna must be isolated as far as possible from the control electronics inside the trailer. If it’s within 12 inches of a control unit, or even a wire to the control, you’ll experience operational problems. It’s best to locate the mobile antenna on the roof ladder, if your rig is so equipped. The ladder will act like a form of ground plane. In your case, I suspect you have a rubber roof that will allow radio-frequency emissions to radiate inside the trailer and mess with the appliance controls. This situation is unhealthy for the occupants, to boot. If you don’t have a metal roof and/or rear-mounted ladder, you can try a couple of fixes. You can shield the electronic controls inside the rig with lightweight copper screen (hard to find, but available at some hardware stores). This can be difficult without easy access to the controls – especially inside the refrigerator -= and you must be careful not to make contact with any part of the control components. You can also place small .01 uF capacitors on those leads that may be picking up the induced radio waves from each lead wire to the chassis ground. |
If you still can’t make the system work, contact electronics guru Gordon West (WB6NOA) at (714) 549-5000. West has written a number of electronics-related articles. If he doesn’t have the answer, you’ll have to quit transmitting – Just kidding. As a ham operator I know words are golden.
Editors note: I’ve heard stories of anti-lock brakes going on, air bags deploying, and surge problems during transmitting with poor mobile installations. I don’t know of any occurrences personally, but this article serves a purpose in illustrating that problems like this can in fact occur. Bert Younglove (WA7AXO) reminded me of a story about one of our common friends, Ed Burke (KI7KW) trying out a new mobile for the first time. He took the microphone and held it outside the door of his vehicle and keyed down several times at the limit of his transmitter. He was trying to see if the air bag would trigger before he got behind the wheel. Many of us have been bit by "RF in the Shack". I guess that having the airbag go off when in the middle of a QSO is just the car’s way of saying "ouch"! Thanks to Max, KB7TMH who gave me a copy of the article to include in the sPARC gap. President and sPARC gap Editor: Vice President and Web Master: Membership Secretary/Treasurer
and 1 yr. Director: Recording Secretary: Not Filled, Available Station Trustee: VE Testing: W7LT Packet BBS SYSOP: |
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