Technical Aspects of QRP - Keynote # 3, 1997
Well, it's time to sit down at the keyboard and pound out another column. Gee, I wish it was as easy as that. A lot of thought goes into these columns. Most of the thinking concerns just what to write about. Once I can come up with a topic, fleshing it out into a column isn't that hard. That's where you can help me out. If there is a specific topic you would like me to write about, please let me know. The ideas for my previous columns have come largely from you. Thanks.
This month, I am writing about the technical aspect of QRP, and that fits in nicely with an idea I received asking about antennas for the QRPer living in an apartment or otherwise restricted in what he can use for an antenna.
First of all, keep in mind that it is very important for the QRPer to have the best sounding signal possible on the air. If it is not going to be an overwhelmingly strong signal to attract attention, then it should attract attention by its cleanness and crispness. That statement was reinforced recently in one of the national magazines when a writer mentioned that a clean, well-keyed QRP signal will often beat out a stronger, but defective (chirpy, buzzy, etc.) or sloppily keyed signal in a pileup.
How do you get that good sounding signal? I don't want this to be an overly technical article telling you that you should use a .01 mfd capacitor in conjunction with a 47 k resistor to change the rise time of your keying waveform, or other things like that. I do want to say that you should check your signal on the air to find out if there is anything wrong with it. This is oftentimes not easy to do, especially if you use a transceiver like the QRP+. This (and I presume other transceivers - not having used any except the QRP+, I can't say for sure) transceiver uses a sidetone monitor for monitoring your keying. This sidetone has nothing to do with your transmitted signal. It may sound great, but you may be transmitting a very chirpy, buzzy, clicky, etc. signal. Don't interpret this as my saying anything bad about the QRP+. Every one of them that I have heard does put out a FB signal. I'm just making a point that it is important to check how your signal actually sounds on the air. Probably the best way to do this is to check with a very good ham friend of yours - one who is not afraid to tell you if something is wrong. Even better would be to swap stations with him so you can hear your own signal.
Now that you've checked your signal, what do you do if you find something wrong? If you are using a home designed and built rig, then you should know enough about it to figure out what is wrong. If not, the publications like the ARRL Handbook, etc. provide a wealth of information to help you figure it out. If you use a kit rig, I am sure that the kit manufacturer is the place to go to find out the cure. The same with a commercially manufactured rig. The company that made the rig wants it to sound good on the air because that is an advertisement for his company, and if you remind him of that when you contact him about the problem, I am sure he will be willing to help you solve the problem.
One quick fix that may be overlooked at times is simply to be sure your battery is fully charged if you use a battery powered rig. Once a battery drops to a certain level, all kind of strange things will happen to your signal, starting off with a slight chirp and progressing to a major frequency drift, then a complete shutdown of your rig.
The next thing to consider is how to get all of that 5 watts (or less) of RF into your antenna? It is important when running QRP that losses in your transmitter, tuner, and antenna itself be kept to a minimum. A station running a KW can afford to lose quite a bit of power in corroded connections or a mismatched antenna system and still be heard very easily on the bands. The QRPer (and really all amateurs) should strive to completely eliminate all losses.
First of all, periodically check all the connections in your antenna system. If you have bolt and nut connections, make sure they are as tight as possible. Remember unless you live somewhere where the temperature is constant the year round, metal parts will contract and expand with temperature changes and that can cause a loose or intermittent connection. The same with connections in your antenna tuner and transmitter. Check them periodically and tighten them if needed. Look at all your solder connections. If you have any doubt about them, resolder them. A solder connection that started out good may deteriorate over the years. Make sure that all connections to ground are good. One thing that puzzled me for a bit was a frequency shift in my VFO. My frequency would jump just enough to be noticeable and annoying. I tried just about everything I could think of to fix it, but nothing seemed to work. It turned out that the piston type trimmer capacitors I use depend on the screw threads making the connection to ground, and apparently they had corroded a bit and were intermittent. Spraying them with contact cleaner and working the piston in and out several times cured the problem. So don't overlook anything.
All the good connections in the world won't help if you have a mismatch between your antenna and transmitter. To be absolutely sure of having a near-perfect match use a setup as follows: Transmitter->SWR Meter->Antenna Tuner->Antenna. Many rigs have built in SWR indicators and antenna tuners. If you are sure you can trust them, fine. If your rig doesn't have them, use an external meter and tuner.
I'll talk about tuners in a moment, but first let's mention something about antennas. The ideal situation, of course, would be to have a huge parcel of land with room for a separate antenna for each band that you operate. Those antennas would be mounted as high as possible, using the lowest loss feedline possible. Enough about pipe dreams. Only a small percentage of amateurs have that situation. Most of us must figure out how to fit some chunk of wire into a tiny city lot or even our attic or apartment itself.
Every situation is different so it is not possible to give a specific answer to what antenna can be used in your apartment or house. For instance some amateurs use a balcony railing for an antenna. That doesn't help you at all if you don't have a balcony. The same with the folks who use their drainspout for an antenna. That's fine if it's metal, but supposing it's made of a non-metallic material. The answer is to take a good look at your situation and figure out what will work for you.
Don't worry!! Just about any piece of wire will work as an antenna. Just string it out as straight and as long as possible - as high as possible. If you can't get it straight, live with the bends and twists. They won't hurt you. The secret is to get the RF to radiate from that wire. That can be done by using an antenna tuner. My tuner is a CLC Tee type tuner as shown in the diagram.
I don't know how well we can reproduce graphics in the Keynote. Tuning the tuner consists of three adjustments - two tuning capacitors and an inductor. Start off by tuning your transmitter for 5 watts output into a dummy load (either 50 or 72 ohms). Once this is done, don't change any settings on the transmitter. Then set the antenna tuner capacitors to mid-range, and short out turns on the coil to get the reflected power as low as possible while the output stays at or very near to 5 watts. When you find a good tap on the coil, adjust the tuning capacitors to reduce the reflected power to zero. If you can't get it quite to zero, move the tap on the coil one turn in or out, and try again. Some combination of the two capacitors and the coil taps will give you 5 watts out and zero reflected power. Make a note of the settings so you can quickly return to them, and proceed to the next band.
If you want to try to duplicate my circuit, it is not necessary to have exact values for the caps and coils. Use whatever you have at hand. If you only work the higher bands, i.e. 40M-10M, the caps and coil can be smaller, for example. To change taps on the coil, you can use alligator clips if you seldom change bands or rig up a rotary switch for fast band changing in contests. Remember to use insulated knobs or couplers on the tuning caps since they are not grounded and could give you an RF burn if you touch the metal shaft directly. Also your body capacitance will detune the tuner without an insulated knob or shaft.
I didn't intend this to be a construction article, so my description of the tuner is somewhat generic. If you are seriously interested in building such a unit, and have specific questions, feel free to ask me via Email or regular mail.
I can get a 1:1 SWR (zero reflected power) on all 9 bands with my tuner using a piece of wire about 100 feet long having many twists and bends that runs out my shack window, up the side of the house, through the attic, and out in a short sloping section into the back yard. Hardly an ideal situation, yet it has provided me with over 13,000 QSO's in all 50 states, all continents, and 125 countries over the past 4 years using 5 watts or less output.
I think too many amateurs are intimidated by antennas, and believe that unless you have the perfect antenna system, you can't succeed. I fell into that category myself regarding 160 Meters. I thought QRP and my simple wire antenna could not possibly work on that band, and so I avoided the band for years. However, two years ago, I decided to try, and was I ever wrong! I have had great success there, working well over 1000 QSO's in 39 states, VE, and VP9. I do have problems working DX on 160 (and 80 as well), but other than that, I do very well. I can usually work 200-250 QSO's in the 160 meter contests each time.
Let me know what you have done with QRP and less than ideal antennas, and I'll pass it along in my column.
Summing up, if you don't have an ideal antenna situation, don't be afraid to try QRP. It will work! Be sure that your signal is as clean and well keyed as possible. That helps also.
Next month some ideas about on-the-air things to do with QRP. Visit my web site at http://home.windstream.net/johnshan/, Email me or write to 478 E. High St., Kittanning, PA 16201-1304. I am always glad to hear from you. Till then, 73.