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SSTV PRIMER Edited by: Jim Sheldon W0EB I. INTRODUCTION Hello, and welcome to the most exciting mode in Amateur Radio today. Well, that is my opinion of course but I think, as you get involved in SSTV, you will find yourself in agreement with me. At the time of this writing, I have only been working SSTV about six months, so I think you will find things pretty easy to learn. The first thing I should point out is that this primer is not intended to be an all out definitive guide to SSTV. I will confine it's scope to Windows based soundcard systems and general station setup and operating procedures. There will only be a smattering of theory thrown in where necessary and you will hear opinions that belong solely to this author. If you would like to learn more about SSTV such as it's history or some of the older operating systems, I suggest searching the web. One other thing to mention is that it would be impossible for me to cover every hook up or software setup situation therefore; I will discuss these subjects in generalized fashion. I would like to encourage everyone to use the various E-mail reflectors, including SSTV-Novice@yahoogroups.com to address specific problems and issues. I am the moderator of the novice group and I have managed to persuade some of the experienced SSTV ops to join the group, so information should be readily available there. Now, it’s time to move on to the basics. II. THE BASICS Let's begin this part of the discussion with a mind-boggling fact about conventional fast scan TV. A standard television signal occupies over five Mhz. of bandwidth! I told you it was mind-boggling! Obviously, if we are going to send any type of video on the crowded HF bands, we need a different approach. That approach of course is Slow Scan Television. SSTV occupies the same amount of bandwidth as a typical SSB signal. There are compromises made for this reduction in bandwidth, the most significant one being that live motion video is not possible. However, if you consider that an SSTV signal can be received around the globe in exotic DX locations, that particular compromise is easy to live with. Another plus in my book is the creative graphics you can do with still pictures. Ok on with the show. An SSTV signal consists of a constant amplitude audio tone, varying only in frequency. A very basic explanation of how it works is that high tones are for bright areas and low tones are for dark areas. To explain any further is beyond the scope of this primer and also taxes the knowledge of the author. Remember, I am a beginner too! There are many different modes of SSTV transmission, but the main two the beginning operators should concern themselves with are Scottie-1 and Martin-1. Scottie-1 is the most popular mode of transmission in the United States while Martin-1 seems to be more favored by our European friends. Secondary consideration should be given to Scottie-2 and Martin-2; speeded up versions of S1 and M1, which are used mainly on VHF and UHF repeaters to shorten transmission times. Some resolution and picture clarity is sacrificed in favor of a shorter duty cycle, but this may well be necessary as most FM rigs were not designed for 100 percent duty cycle and some don’t have provisions for reducing power. Now that we have covered the preferred modes of operation, let’s move on to the necessary station equipment. III. EQUIPMENT This section of the primer will start out listing essential equipment and then move on to things that I consider optional. Please note that just because I consider something optional doesn't mean it is for everyone. This section will probably be heavier with my opinions than any other so you have been fairly warned! First of all, the most obvious piece of equipment is the radio itself. The rig used for SSTV should be stable. No one wants to chase you up and down the band trying to get good copy on your signal. I will leave it to the experts to comment on the suitability of tube gear but I suppose if the rig doesn't drift once it is properly warmed up that it should be ok. This is, however, less of an issue today, as most of the better Slow Scan programs have "Automatic Frequency Control" (AFC) built in and will track the signal over a limited range. The computer is next on our agenda. My main piece of advice here is to make sure your computer has the power to run the software you are using. In my book there is nothing more frustrating than trying to run a program on an underpowered machine. Look around at the software that is available and I think you will find some with varying degrees of CPU "appetite". If you are in love with a particular program but don't have the computer to run it, you can always upgrade. This is a great excuse to run by the XYL or OM as reason to buy a new computer! Your computer should be at least a Pentium class, with a speed of 133 MHz or better. I consider this to be the absolute minimum and unless it is a P133 MMX it still may not be fast enough for many of the available programs. Though you may get lucky, you should not even consider using an older 486 computer to run any of the sound card based ham radio programs. The 486 just doesn’t have the processing power to perform the necessary operations and you will only get discouraged trying to make it work. Speaking of software, be sure to look around and try every program you can get your hands on. Most of it is shareware and some is even free. There is no need to rush. Make an informed decision especially if you are going to pay to register the program. Everyone seems to have a favorite. I have one but in the interest of being impartial I won't divulge it here. Catch me on the air, if you really want to know! Next, we need an interface to connect the computer soundcard to the rig. Here you have the option to buy or build. I always build my stuff whenever possible and if this is the route you choose, you can find plenty of good circuit diagrams on the web. If you would prefer to buy, there are several high quality units out there that will do a fine job. Of course, if you already have an interface for PSK or other soundcard modes, you are in business. On the subject of computer soundcards, I should point out that some operators have reported problems with onboard sound systems. This is not to say they don't work. Experiment, but be prepared for the possibility of purchasing a plug in card. Price does not always indicate performance in this case. Many bargain type cards will do the job just fine. For the most part as long as you have the "big three"; your rig, computer and interface, you can operate SSTV. You can obtain your initial images from the web to start out with. Pick a subject you are interested in and use one of the search engines to locate pictures related to that subject. That is how I started. The first item I would put on the list of optional equipment is a computer image scanner. An added benefit of buying an inexpensive scanner; most come bundled with a reasonable photo and graphic editing package Most photo developers put pictures on a CD ROM or other computer type media, which will allow you to import the images into your SSTV or graphics program. A digital camera is also nice to have but is not absolutely necessary. A web cam will allow transmission of "on the spot" pictures of your shack. A frame grabber will enable the capture of images of TV or video. There is also some very sophisticated graphics software available but some programs have a fair amount of that capability built in. This list could go on forever but I will close by telling the prospective operator not to be overwhelmed by it. You may very well have some of the items mentioned already and as you get deeper into SSTV you will know what you want. Time to move on to setup and operation. IV. SET UP AND OPERATION One of the first points I should touch on in this section is rig duty cycle. Remember that it was stated earlier that an SSTV signal is a continuous audio tone, which varies only in frequency. Sending an SSTV signal is much like keying down your transmitter for an extended period of time. Not wonderful treatment for the finals! For this reason most rigs should be operated at a fifty percent duty cycle or about half of their normal output. This can be accomplished by the use of the mic gain control in concert with the windows mixer volume control. I usually set my mic gain as I would for a normal SSB QSO and then adjust the windows volume for about fifty watts of output from my one hundred watt radio. This usually gives a clean signal. NEVER USE THE SPEECH PROCESSOR on SSTV. Another thing that I should mention is that it's ok to have an ALC reading on SSTV as long as it's not excessive. Those of you who operate PSK know these are entirely different circumstances from that mode. Setting the input volume to your soundcard can be accomplished with the line in or recording control on your windows mixer. Most programs have an indicator for input volume along with guidelines for setting it. (Editor’s note on using FM rigs on VHF and UHF: don’t use high power. The duty cycle of the SSTV signal will make short work of your final stages. Cut back to medium or even low power if the rig has this capability and you can still hit the repeater. If you must use high power, give the rig a good rest between picture transmissions. This is a good rule to follow even with HF rigs.) Now that we have our TX and RX ready, let's try to receive a picture. The best place to find activity is probably twenty meters at 14.230 or 14.233. Many programs have tuning indicators but if you stay on these frequencies or tune in the operators voice, you should be able to copy a picture fine. In a perfect world your first received picture will be straight with no slant but most of the time receive slant will have to be adjusted. This is because the clock frequency on soundcards can vary widely. The various programs have different procedures for slant adjustment, and this is one place you will have to read your program documentation. Next adjustment is the transmit offset. In some cases once receive slant is set, the transmit slant will be right on the money also. If you are like me though, you are going to have to make an adjustment. This can be done with the help of another operator who can guide you in which direction to move the offset in order to get your transmitted picture straight. Again, you should be able to find help on 14.230. SSTV operators are some of the friendliest people you will ever meet. Once you have help, QSY to a clear frequency to make the adjustment, as it can be time consuming and this particular frequency is usually very busy. Well now, if things have gone as planned you have been able to interface your soundcard and radio with no major problems. Your receive and transmit should be slant free and you should be able to start exchanging pictures with other amateurs. If you are having problems with RF in the computer or have hook-up questions I suggest you post an inquiry with specific details on one of the E-mail reflectors. Chances are good that someone has run into your particular problem before and will be able to assist you in solving it. SSTV is like any other mode in that it has it's own unique operating practices and etiquette so now that we have a functioning station set up we will look into these next. V.OPERATING PRACTICES AND ETIQUETTE There are a couple of different ways to establish contact when working this mode. One which is obvious, calling CQ, has some quirks of it's own on SSTV. Sometimes a simple voice call of "CQ SSTV, this is...." will net you a contact right away. In other cases you might want to send a CQ picture along with calls on voice. Do not, under any circumstances, fire up and start sending one picture after the other without any reasonable pause. You are not a broadcast station and this is a very annoying practice. The object is to establish contact not put on a slide show. I have also heard stations call "QRZed SSTV and while I can't tell you this is wrong, it does not seem logical to me. No one is calling you, you are seeking a contact, so I would stick with CQ. The time-honored tradition of first asking if a frequency is in use is also especially important in SSTV. Many times I have tuned to one of the popular frequencies and heard silence only to hear video transmission seconds later. The reason for this is pretty simple. Sometimes an operator will pause for a few seconds after a voice transmission while they are loading their next picture. You can't always find the one you want and computers are notorious for glitches at the most inopportune times. Calling CQ or blasting video into the middle of an established QSO or roundtable is no way to make friends. Propagation on the HF bands is another factor. Someone you can’t hear may be sending a picture to a station that may be S9 to you. If you start sending a picture, you will wipe out, or severely damage the picture he was receiving. It’s an absolute necessity to listen for at least 5 minutes on HF to insure an unused frequency prior to making any calls. A roundtable is the other way to net SSTV contacts. It is also the most enjoyable way of working the mode if you ask me. Wait for a break in the conversation and drop in your call. There is usually one person keeping a list of callsigns and they will acknowledge you and notify you when it's your turn to send a picture. Think of them as the control operator of an informal net. In fact, many people refer to these roundtables as nets so I suppose the terms are pretty much interchangeable. When working in one of these "nets" you will sometimes hear a station describe another one's transmission as "closed circuit". This is an obvious indication that the picture came in clearly with very little interference or noise. This is a fine way to describe reception in most cases but SSTV does have it's own signal report system. It is almost exactly the same as the RST system used in CW except for one important difference. In SSTV we report Readability, Signal strength, and Video or RSV. Video is reported on a scale of 1 to 5 so a perfect signal would be RSV 595. This system is used mostly in DX contacts and is usually added as text to a picture before transmission. Video QSL cards are also sometimes sent although it still takes the old fashioned postcard for confirmation when seeking awards. Speaking of DX, I must caution newcomers against a practice that I have observed on some occasions. Do not send partial pictures or picture headers with your call on them with the intent of snagging a DX contact. This causes the receive system in the software to constantly reset to the top of the screen with every short transmission. This is extremely annoying and clutters up the band. The SSTV DX community takes a dim view of such operation. One last point of operation that I should cover here is announcing the mode of transmission before sending the picture. Generally, after a short introduction of the picture you intend to send, it is customary to announce your mode of transmission. Such as, "this is W4HIJ, Scottie-1 video". Even though most software can automatically determine the mode a particular picture is being sent in, this short announcement keeps anyone from being caught off guard and gives them a chance to set the proper mode in the off-chance their software didn’t catch the start signal. Etiquette or manners is something that has been sorely missed in amateur radio over the past few years. Fortunately with the recent emphasis on enforcement issues by the FCC and through the efforts of Riley Hollingsworth this situation is changing for the better. Now I hate to jump up on a soapbox here, but there are certain facets of this subject that need to be discussed as they pertain to SSTV. Once again, this is an area where the authors opinions will find there way into the discussion. It is impossible for this not to happen and not everyone is going to agree with me. I hope that for the most part though, that you will find the following passages to be composed of good common sense. I'm going to come out swinging here and tackle what I perceive to be a very real problem on the twenty meter band. I am talking about stations which run excessive power. The FCC rules clearly state that one should use the minimum power neccessary to maintain reliable communications. This rule should be observed on SSTV as well as any other mode. Unfortunately, some of our SSB bretheren up and down the band from 14.230 don't observe this rule very well. This frequency is one of the most popular for SSTV and it is ashamed the amount of splatter and interference we have to battle to use it. As you can probably surmise this infuriates me. However, I don't think we should start a power war. Remember, "Never argue with a fool , people may not know the difference." No one wins these battles anyway. If you have an amplifier then by all means use it when it is neccessary. The key phrase being "when it is neccessary." Otherwise follow good operating practice and abide by the rule stated above. I will have a short discussion of tune up and use of amplifiers later in the primer. One problematic issue for SSTV operators in today's politically correct world is picture content. By this I mean what should and should not be sent over the airwaves.What follows is generally the standard rule. NEVER SEND PORNOGRAPHIC OR OTHERWISE OBSCENE IMAGES ON SSTV! Now, as we all know different people have different standards in this world and right here I am going to express a personal opinion. I for one, see nothing wrong with sending an occasional picture of a bikini clad young lady. I only mention this because you will see such pictures. There are some people who vehemently disagree with those that send them. The best advice I can give anyone here is to use common sense. There is a time and place for everything. You certainly would not want to send such a picture when in contact with a YL or to a father demonstrating SSTV to his daughters third grade class. Believe it or not I have seen behaviour almost as bad as this. Now that you have heard my opinion on this I would suggest that you follow your own personal principles but don't chastise someone if they happen to differ with you. Enough said. Sooner or later you will see a political cartoon cross your screen. In my opinion discussion of politics has no place in Amateur radio but here again, some people will disagree. If you see a cartoon or hear a comment that goes against your political views I would just let it go. No one wins these type of battles anymore than power battles and usually the whole of the group listening suffers. In case your'e wondering, I am not even going to address religion here. That subject is ones own personal business. One last reminder or disclaimer if you will. In the preceding passage, part of what you have read are one man's personal opinions. You or anyone else are free to differ with them in part or in whole. Just please don't villify this author for expressing them. Remember that SSTV is supposed to be fun! That's why we do it. VI. ODDS AND ENDS Well, for want of a better title that's really what this section is. SSTV is such a multi-faceted mode that there is no way to cover everything in a primer such as this. In wrapping this baby up I will, as promised, touch on the subject of amplifiers and their tune up as well as explore a small portion of the remaining possibilities available to the aspiring SSTV afficianado. Amplifiers that are put in use for SSTV service have to be handled with kid gloves in a manner of speaking. Let's look back at when we discussed the duty cycle of your radio. The same rules are going to apply to an amplifier but there are other precautions that should be taken also. First of all, let's get the amplifier tuned up in a normal fashion. Follow your unit's recomended tuning procedure and tune for full output. Now, put the amp in standby and tune your rig for about half of it's normal power output as outlined earlier. Switch the amp to operate and apply drive power. What we are after here is 300 to 400 watts of output from a one kilowatt amplifier. You may have to tweak the amps plate and load controls to get optimum output with the reduced amount of drive. By the way, make sure that the transmitter's carrier control has been set to minimum! On some amplifiers like my Kenwood TL-922A there is a mode switch to select CW or SSB. This switch does not change the class the amp runs in but rather the amount of plate voltage. In the case of the TL-922A it switches between 2000 volts for CW and 3000 for SSB. If your amp has such a switch, it is advisable to select the lowest plate voltage. Ok, now that we are tuned up it is time to send a picture. Go ahead and start something in Scottie-1. Hopefully, you can see your power tubes through some ventilation holes in the amp. If everything looks nice and cool let the entire picture go out. If at any time you see much more than a slight glow from the tube plates or smell heat cease transmission immediately! Power tubes cost to much money to put at risk. You can try retuning the amplifier or reducing output some more but if you can't get satisfactory results stop and submit a post to our old friend, the E-mail reflector. There should be someone running the same model of amplifier as you are or another person that can assist you in some fashion. Remember, it is not worth risking your tubes over. Now let's explore some of the other exciting aspects of SSTV operation. This will be just a brief description of some specialized interest. I encourage you to research anything here that appeals to you. HF SSTV repeaters can be a fun diversion from day to day QSO's. Most of them require a tone to activate after which they will respond by sending the letter K in CW meaning that it is time to transmit your picture. The tone is usually a frequency of 1750 Hz although this can vary. Your program should have provisions for sending several different frequency tones. Operating frequencies and tone information for various repeaters can be found on the web. VHF/UHF SSTV operation is popular in some areas of the country. This can be done using a common FM transceiver. Some operation is simplex but in many cases repeater owners set aside a special day and time where the repeater is made available for exclusive SSTV operation. Check with your local club to see if there is any activity in your area. Last but not least is satellite operation. This takes more equipment and is not that easy to do but from what I understand it can be quite exciting. I have not been fortunate enough to experience it so I can only give it a brief mention here. Well, I think that is going to about wrap it up. I hope this primer will be of use to a great many beginning SSTV operators out there. Jim and I have had a lot of fun writing and putting it together. We have also had a lot of E-mail traffic! If you need more help or have a specific question, don't be afraid to ask. You can ask on the reflectors or on the air. As I said before SSTV op's are some very nice people and most will be glad to help a newcomer. The more the merrier! We hope to "see" some of you new guys on the air soon! 73 and good luck, |