MO&O DE TR 061103 - First Memorandum "Your Antenna has only Two Ends" MO&O in my case means "Memorandum, Opinion, and Ought-to-be." "TR" is my sine, that's S-I-N-E and it is a telegraphers name, usually written without quotation marks. A sine can be someone's initials, but more often it is something that makes a pattern in International Morse Code. In my case _ ._. Where I hang my hat lots of hams use sines. One rule though, if someone else in your office already has your sine you must pick another. Feel free to quote me, but be sure you spell my name right,.. That's TR. Enough getting acquainted! Did you know your antenna has only two ends? I forgot about it until this week; it's amazing what you can forget in over 40 years. I put up a 40 meter dipole tuned near 7,000 KHz on low end and fed it in the center with a piece of coax. Up on 15 it is resonant near 21,600 KHz. I was surprised that on the third harmonic the resonant point was higher instead of lower than 7 X 3. If I could forget that, I thought I'd pass it along in this first memorandum, maybe someone else could forget too. 40 Meters /------------|------------/ 15 Meters /---------\----|----\---------/ One half wave on 40, three half waves on 15. Notice on 15 the half wave in the center has no ends on it, and no end effects to make it think it is longer. A good way to measure an antenna is to run a wire from Support A to Support B. Pick the tallest trees you can find, and don't worry if they're on a neighbor's property, that's what front doors are for. Go to the door and ask permission; if it's given great! If not, pick two more end supports. After you've got your wire up start to "figure" on the trees swaying in the wind. If they sway apart, no problem, that's what counterweights are for, but if they swing together, and the counter weight rope lead doesn't have enough length, the end insulator will hit the pulley and your antenna will sag big time. When the trees open up in the wind cycle it will give a jolt that may bring down the antenna. Be careful not to get too greedy. When you're hopeful it is the longest highest antenna you can get, lower it down, fold it in half and cut it right in the middle. Put up some home made open line on it and be very particular about the length of that feed line. It must be long enough to reach between your shack and the antenna. Too long, and too much sag, too short and it will jerk the antenna around just as if you had gotten greedy with the length between the trees. Bring it down to a nice swinging link tuner that will match ANYTHING and you're ready to start GETTING OUT! I've been doing that most of my life. Please notice I didn't say anything in the above discussion about resonance or half waves. Someday when you have time on your hands, go down to the city library and go into the reference area. Look up some books on Broadcast Engineering, it will be educational. Engineers measure antennas in electrical degrees, efficiencies and angles of effective radiation. They're also interested in Effective Radiated Power and directional properties. You won't find much about half wave resonances and tuned feed lines. There have been broadcasting stations on the air now since 1921 and really, the subject has been researched very thoroughly. In a future memorandum I'll pass on some quick, easy, and cheap ways to make your own open line. It sure is a lot cheaper than coax. That sure was a great SWR article in QST this month wasn't it? November 2006 page 37. I heard some of the guys talking about it this week. Pretty good eh? I was especially impressed by the words VWSR standing for Voltage Standing Wave Ratio and and about half a paragraph below this gem it says "The voltage travels down the feed line..." Obviously I received a poor education. You have to hand it to the league, that's why they kicked out Walter Maxwell in the antenna books, the guy is just a dummy. Oh say, when was the last time you saw a good engineering job advertised in QST? Where I come from, guys don't put their ham licenses on their resumes. I'm tempted to write I'm a dummy too, but I think it would be presumptuous and embarrassing to put myself too closely with Walter Maxwell; he is someone I really admire. I'm posting these memorandums on the web at http://www.radions.net/mo&o_de_tr.txt My ISP doesn't accept uppercase letters in it's web hosting, although you may be able to get away with that on your browser. Be sure to go into your IE browser and bring down the "View" menu. Under "Text Size" pick a value that displays on your screen without the words running off the end of the screen or being unduly small to read. You can e-mail me at http://www.radions.net/spamfltr.htm I promise to write another one of these memorandums next month and - oh - I guess till I get tired of doing it or you guys get tired of reading them. VY 73, & "God Bless" DE TR MO&O DE TR 070402 - Second Memorandum "How I make Ladder-Line" Air is such a wonderful dielectric! Consider that your signals are radiated from the antenna and travel through air (the either) to their destination with remarkably little attenuation; the only dielectric better than air is a vacuum. One key to good ladder-line is to have the maximum amount of air and the minimum amount of intervening material that is not air. At commercial stations, the wires are drawn taught with high tension between supports and there are no "ladders." My favorite "ladders" are swizzle sticks used for mixed drinks. You can buy them very inexpensively at the grocery store in the liquor department. Get a big bundle and they will last a VERY long time! As a rule I cut them in half before using them, and you don't need very many. Take two pieces of wire, I'm partial to #18, but you can use any thickness. What I like about #18 is it is thin enough to be malleable and strong enough to last many years. Pick any two good supports in the back yard, I like doorknobs, fence posts, thick branches on trees etc. Stretch two wires between the supports as tightly as you reasonably can, just leaving a tiny bit of sag. If you get 'tinned" wire, soft drawn copper with a shiny silver like finish that is the best sort. The tinning will tarnish quickly giving your feed line near invisibility. Usually I make the antenna out of the same wire and for the same reason. Visibility is important at my house. Soft cotton handkerchiefs work best for me, but I suppose you could use paper towels, the important thing is to safe guard your fingers from friction and irregularities in the wire. Take each wire, one at a time and place it in your hand with the four fingers in the direction of your travel and then press down with your thumb far enough to bend the wire. You need to plan on not looking where you're going, and keeping a sharp eye over your shoulder as you walk backwards, or else cross your arm across your body to hold the wire close to your waist as you walk forward. In any event, progress from one end of the first wire to the other end of the first wire bending it under your thumb as you go, then returning with the same motion on the same piece of wire. Repeat now for the other feed wire. With every trip back and forth you will find the sharp bends in the wire releasing and the wires will sag farther and farther. It will be necessary to stop and refasten them when the sag becomes too great. After many trips back and forth you will decide the wire has no significant sharp bends and you will become concerned that the wire is "curling" from the repeated trips bending it back and forth. With just a slight amount of sag begin to insert your half swizzle stick ladders into the line. Cut up a goodly amount of #18 tinned wire into short pieces perhaps 3 inches apiece. My "rule of thumb" is to put a ladder in at every foot for every inch of separation. If the wire is spread 2 inches, I insert a ladder every two feet. Lay your first spreader at a mid-point between the end supports and take one of the 3" tie wraps and put the middle around the spreader and the feed line. On one side twist clockwise, and on the other counter clockwise. When you're done, the tie wire should form a spiral in the same direction as it goes along the feed wire with the ladder caught in a "Pocket" between the feed wire and the tie wire. If you have an extension cord or a butane soldering iron it is nice, but not necessary, to solder the feed wire to the tie wire at each end of the tie wire, but be sure to allow the opening to remain for the ladder along with some open space before the solder flow. Take a couple of needle nose pliers and squeeze the tie wire against the feed wire so that the swizzle stick is slightly crushed flat. It should have significant friction, but not enough to sever the plastic. Now do the other side. of the feed line. Do the rest of the feed line without soldering, then remove the ladders and go back and solder them all, reinsert the ladders and crush them with the pliers; it's a much faster assembly that way. As you approach the ends, the tension across the spreaders will press them together with ever greater force and you will need to release tension on the wires and increase sag. When you do that, the feed line will begin to curl. Go back and use the four finger-thumb adjustment between ladders and bend it in a direction opposite to the curl. Eventually the feed wires will be straight and you will have beautiful cheap ladder line. Get an insulator that is strong and about the same length as your ladders to use at the top of the line and another one to use at the bottom end. You may have a problem finding just the right insulator, but I've had success with the little egg ceramic or plastic insulators they sell down at HSC, they are close to the right length. for me. It doesn't have to be exact. Take one end of the feed line at about the same length you would insert the next ladder, if you were using a ladder, and cut the feed wires just beyond that point. Form a loop around the ends of the egg insulator that is big enough the loop can "wiggle" freely around the insulator. Twist the ends and solder them to form the loop so it can't fall off. Now, likewise the ends of the antenna, they also, are in a loop around the end with plenty of wiggle room. The objective is that when the antenna swings in the wind the wires don't bend and fall off from metal fatigue. The loop and the insulator form a "bearing" of sorts that absorbs the movement without bending the wire. Now, take a longer piece of #18 tinned, perhaps a foot long and wind it around the antenna and feed line wires. Two pieces, one on each side of the insulator and the tie wire forms a loop that is "outward" from the insulator. At the point the tie wires touch the feed line and antenna wire they twist inward towards the insulator. They will make a big circle, but not so big they flop over each other. Solder them and be sure you are a reasonable distance away from the insulator. Hoist your antenna up in the air a little at a time allowing the feed line to follow laying on the ground. If your yard is like mine they will catch on the grass and the weeds, stones, and other irregularities, so you need to be watchful as it goes up a little at a time, stopping to "curl" any bends that appear in the vertical feed line as it goes up. With your antenna fully raised take the loose end of the feed line and bring it over to your house. Insert another strong insulator at a point that allows a graceful bend in the feed line. I like it to go away from the house horizontally at a point high enough that someone won't walk into it. Usually I attach it to the eaves while on a step ladder. Do the same procedure as at the top of the feed line, this time not cutting the feed wires, taking them and passing them through the eye of the insulator and then twisting a loop and soldering it so the wire is free to move about the lower insulator. Drop the feed lines down alongside the house and put more spreaders in them until you reach the point of entry into the house. At the top end, put two more one foot pieces of tie wires around the ends of the insulators and bring them up to two nails on the inside of the eaves slanting up. Solder everything and hook the loops over the ends of the two nails. Use galvanized nails so they don't rust even though they are on the inside of the facia where the rain won't reach. Don't be cheap, go to the store and buy a couple of small nails. Go through the wall of your dwelling. This is a subject of debate. One easy way is to go through a door jamb, bending the wires so they conform to the door. Another time honored favorite is to go through a double sash window at the top or bottom, preferably the top again conforming the wires. If you have no point of entry that is easy, you will have to drill holes. If you have a window with small panes, remove it if you can and take it to a glazer, removing one small pane and replacing it with a pane of plastic in place of the glass and drill two holes in the plastic. A glazer can drill holes in glass and give you entry that way. If you have no window, or if the window cannot be removed, then you have to go through the wall. Go down to the hardware store and buy a long bit of small diameter big enough to give room for your wire, and long enough to go through the wall. Try to find the studs in the wall and stay away from wires that might be carrying 117 volts. If you can't do this yourself, hire a handyman who can. You may have to pay him something and don't be cheap about it. Take a couple of insulated wires and push them through the holes. Bend the ends on each side into a small loop and attach your feed line inside and outside to the eyes and solder them. Don't forget to weather proof inside and outside with some liquid silicone that will set to a firm seal. Inside continue your ladder line down to what ever tuner you have. Put a short piece of coax on the tuner to an SWR bridge and another link to the rig and you're done. Your load will probably be very reactive on at least some bands, so you will either need a good tuner, or else use lumped constants. Those 3:1 tuners they put inside the transceivers will probably not be up to the job on all bands. This discussion is beyond the scope of this article and I will have to talk about it in a future article at a later date. The sun will rot the swizzle sticks in about two years. If your feed line has been made of soft drawn tinned #18, it will hang straight of it's own weight as time passes and as the ladders begin to rot and fall out, the feed line will remain in perfect spacing, without any ladders. When the wind blows, the feed wires will swing, and at some point when enough ladders are gone they will swing into each other. By that time you will have only a few ladders left instead of the many you started with. Carefully lower the antenna and insert only enough ladders to correct the problem. It shouldn't take more than 10 minutes for a feed line of 50 feet or less. May I assure you, you will have a VERY efficient antenna! You will get good signal reports on all bands. Remember my first article, make the antenna stretch from point A to point B etc, and don't worry about how long it is. Anything flat top over 3/8 wave will produce good results. If you want to go a lower band, tie the feeders together and drive them against ground. VY 73, & "God Bless" DE TR MO&O DE TR 070428 - Third Memorandum "Lumped Constants" When we last concluded memorandum two, I wrote that the existing antenna system, built without any regard to length of antenna or feed line, other than the necessary dimension of being from point A to Point B using available supports and a feed line of a dimension running from antenna to shack would almost certainly be highly reactive on one or more bands, indeed probably on all bands. I made a passing comment that it was certainly beyond the limits of the usual 3:1 matching tuner built into the modern transceivers unless Lumped Constants were used, and further, that this was a subject beyond the scope of the Second Memorandum Article. Although it is slightly off topic here, let me begin by quoting one of my favorite antenna authorities, L.B. Cebik http://www.cebik.com/vhf/bbeam.html and just above Fig. 5 he says "For simple antennas, my favorite support material is PVC, which should be RF transparent well into the VHF range, if not higher." L.B. has graciously written to me in regard to this, "I do not mind disagreements on the general subject of PVC. Actually, the available material varies considerably around the country to meet local building and plumbing (but not radio) codes. So many places have additives that may be unique to a region. For example, in the NW, PVC (white) apparently does not have the level of UV protection that it has in the East and SE. Additives may also disturb the RF transparency. I rarely recommend PVC for other than boom and mast duty, although some folks like to place elements inside it. Those two different applications require very different levels of non-conductivity. However, I have never had any vertical beams detune when using a SE-variety of PVC for the mast--at least not through 2 meters. There are better materials for all but very non-critical applications from 70 cm upward." Having had the privilege of LB's allowing me to quote him, and also having received a reply quoted above, I would like to recommend it to you for careful consideration. L.B. is a respected authority and anything he might have to say merits our respect. My experience has been that very few FM and Television Stations construct their transmission lines using PVC. They use "hard-line" copper tubing, 4-inch outside diameter, sometimes greater diameters, with a smaller inside diameter copper tube supported by Teflon "fingers" in a rotating pattern, usually using very few "fingers" for a 20 foot length. In higher power installations such as on Mt. Sutro in San Francisco with runs of nearly 900 feet, the transmission lines are pressurized with dry nitrogen gas; some substances are more "transparent" than others. In my previous Second Memorandum I Wrote about the "wonderful" qualities of air as a dielectric and commented that only a vacuum exceeded it. Alas, this is not quite true and I know of an unfortunate example of a 4-inch Hard Line at KOIT in San Francisco where the technician went home one night without leaving the nitrogen set to maintain pressure. In the middle of the night, the line arced over melting the inside and outside copper tubing, thus throwing the station off the air. For his employment, this was major mistake. Anyway, with all these disclaimers, I would like to recommend against the use of PVC, Bakelite, or other plastics, unless it is of a known high dielectric quality in the construction of Lumped Constants. I prefer to mount my constants supported by bare alligator clips (bare metal only) and the constant be made self supporting by using adequately sized alligator clips and wires so that they hang in mid-air. My favorite place is somewhere convenient to the operator, bringing the ladder line out of the tuner over to a convenient position, having a bright clean bare copper surface available and the constant can just be clipped across the open line. I am fond of self supporting coils with no plastic ribs made of sufficiently large wire that they are rigid. I don't envision running 1500 watts into #18 tinned open wire lead, but 100 or even 300 Watts should be acceptable and I've done that for many years with a home brew amp that uses a pair of 811's. I've never had a problem, but that doesn't mean you won't. You just need to use caution. L.B. Cebik has an excellent web page on this subject at: http://www.cebik.com/load/loadtl4.html and I thought it made excellent reading. When using capacitors, I am fond of "doorknob" ceramic transmitting types such as found on the Butternut Antennas. One property I want to caution you about is RF Current ratings of capacitors. 200 Volts and 200 pF is most definitely NOT a way to pick out capacitor constants for your line, probably even if you run QRP. Coils you can wind yourself cheaply, making sure they are about twice the length as their diameter, and making sure the windings are separated by at least their conductor thickness by plain air, and by being sure there is no insulation on the wires. Yes, I will admit if you find some Teflon insulated wire, particularly if it is silver plated, that would probably be a better choice, but really I don't think it's likely you will come across that by accident. Capacitors are an entirely different matter, it may be possible to find an old air variable cap and place it across the line at VERY low power to find an advantageous setting, then using a Grid Dip Meter or one of the newer DMM's that has a capacitance bridge measure built in to find your value; then try to obtain some ceramic doorknob capacitors with values close to that. By going up and down the line at various points you will find the inductance or capacitance needed will vary, even requiring exchanging the constants, a capacitor or inductor to achieve a match. On no account, should you expect this exercise to solve all of your woes, you can indeed, feel fortunate if it does. One shining failure is where the equal but opposite sign of lumped constant cancels all the reactance, but the resistive component is outside the matching ability of the tuner. I don't mean to discourage you at too great an extent, even with a 3:1 transceiver tuner you can still match quite a good variety of impedances, and it surely isn't needful that you present your rig with a purely resistive load. If it matches, that's almost good enough. You should use an SWR bridge between the rig and the line going to the tuner, or if the tuner is internal to the rig, put the SWR bridge before a 4:1 balun with the line attached. Try to give your rig some reasonable SWR value here. Which now brings us to our next subject: The "Dreaded Stub." If you're still with me this far, don't despair, there is an excellent write up in the "West Coast Handbook," Bill Orr, W6SAI, Radio Handbook, nineteenth edition, Page 25.22 Reading from "Matching Stubs" to "Linear R-F Transformers." I must at this point share with you my inability to perform the kind of math that L.B. Cebik and many engineers are so adept at. I have not graduated from college and I am just a lowly technician. I'm sure many of you will forgive my inability, suffering the same fate as myself. Therefore, I refer you to Bill Orr's book, the only tome which I have ever been able to understand, and it has served me well on many, many occasions. You may believe me, when the chips are down, a stub will save the situation. We proceed now into the "cut and try" territory of "no math." Cut a piece of TV-TwinLead about 6 inches long and short one end. Put a piece of electrical tape over the short just to be sure you don't touch it to anything. The open end may be placed across a small flashlight bulb. Couple a small amount of power into your feed line, picking a time of day when the band you're working on will have little or no propagation. 40-meters being the exception where you can put two or three watts into the feed line nicely zero beat with the BBC or some other strong broadcast carrier. The objective is to cause minimum QRM when you do this exercise. Take your "sled" consisting of light bulb and TV-TwinLead and holding it closely to the open line run it up and down the line and observe that the lamp becomes brighter and dimmer as you traverse the standing waves. At the points where the lamp is brightest it is a current maxima and where the lamp is dim a voltage maxima. You will observe that the SWR on the line is like a sine wave and it is really impossible to determine where the lamp is brightest or most dim. That is why it is necessary to take our reading at a mid-point half way between the bright & dim points, and at this midway point the intensity of the lamp is rapidly changing. Get a piece of paper and put a spot of grease on it. If it is night, you will have no problem, but if it is day you will need a shade to block the sun. Hold the sled at a constant distance from the feed line, and hold the paper at a constant distance from the sled. Be careful not to burn out your lamp! View the lamp through the edge of the grease spot on the paper. Any sort of grease will do, my personal favorite is cooking oil that my wife keeps in her kitchen. Anyway, at some point as the light becomes brighter, the grease spot will conduct more light than the paper that is not greased, and at some other point the grease spot will conduct less light than the paper. You are looking for the place on the line that the grease spot is the same brightness as the paper next to it and you are unable to tell where the grease spot begins and ends. Mark this spot on the line with a small piece of tape or a colored marker. Then go to the other side of the voltage maxima (where the lamp is most dim) and find where the grease and paper have equal brightness, mark this point also on the open line. Take a tape measure and find the number of inches or feet between the two marks and divide by two. Yes, you are looking for the exact midpoint between the two marks. This point will be the zenith of the voltage curve of the SWR sine on the line. Keep in mind that although you may have been very careful in this exercise, your end result will not be exact, only "close." In my work as a transmitter technician, I had access to a sled built expressly for this purpose at KPH, and it was equipped with a sensitive RF meter that gave me truly wonderful accuracy. Should you be so fortunate, disregard the above discussion about grease spots and paper, use your meter across the open end of your sled. It will be easier and much more accurate. In any event you now have found the voltage maxima on your line and you are ready to begin measuring. From the formula 234/Mhz calculate the length of a quarter wave on the band for which you need. If this is too difficult, continue your paper and grease exercise to the next point of equal brightness and mark it on the open line. Measure the distance between the two points and find the middle. This will be your current maxima of the SWR sine, and if you measure the distance between the two maximas you will find one half wave. Divide this in half and you will have the distance of a quarter wave. Again, we have "no-math." Build a length of open line as outlined in memorandum two and make it a quarter wave in length. Put a couple of alligator clips on one end of the line that face up so your stub may be clipped across the feed line. Take two more alligator clips and arrange a short length of wire so that it may be clipped across your stub at the lower end of the quarter wave as a short. Keep the shorting wire between the two alligator clips short. Take your newly made stub and fold it in "thirds", then mark the points of 33% and 66% on the stub and straighten it out. Leave the bottom end of the stub open and attach your shorting alligator clips at the point that is 33% from the bottom. Using a tape measure, find how many inches/feet the short is from the bottom of the stub. On the feed line measure back from the voltage maxima toward a current maxims (either side is fine), this same distance and attach the top of your stub. Place a small amount of power into the feed line and see if you have a match. Can you match it? What is the SWR between the 4:1 balun and the antenna tuner? Can you read it? Make a note of your settings and then turn off the power and then move the shorting alligator clips at the bottom of the stub 10% of the distance of the stub either up or down. Now turn on the power again. What is the effect on your match? If things are looking good, continue to adjust the shorting clips up and down and the attachment to the line by equal distances, until you find the most advantageous position, then move the point at which the stub is attached to the feed line back and forth in small increments. Continue this exercise until you get a perfect 1:1 SWR on the bridge between the balun and the tuner, or you are satisfied that the line is an easy match for the tuner and it is "good enough" for you. Remember power lost in the stub will almost certainly be less than power lost in the tuner, if there is a high SWR at the tuner, but when the SWR at the tuner becomes low, perhaps let us speculate 5:1 the power lost in the tuner will become so little it is not worth us worrying about, and we may stop working on a "perfect" match. Let us assume now that the above exercise has given us no relief. Go to the point of 66% from the end of the stub and continue as before. This is what is known as "cut and try." Keep experimenting until you find a match. Again we are using "no-math." There are ways to calculate the point of line attachment and stub length, and if you are able, L.B. Cebik's web page will save you considerable time. Using the "West Coast Handbook" I was smart enough to calculate the stub points, and you may also save yourself some time doing this. In any event, you will end up doing some "cut and try" work before you are finished. Now you have a stub on that band, and you can proceed to make stubs for other bands you need; AND you know how to do it with "no-math!" Believe me, it sounds much harder than it is, and once you have done it the first time you will develop a "feel" for it very rapidly, and it will go smoothly and easily. It's the same as making open ladder line, you will wonder why others avoid it, it is so E-A-S-Y-!-!-! All right, now then, what we have been doing is called closed stubs. If you have less than a quarter wave of a closed stub, you have an inductance. If you like having ladders hanging down, then fine, but if you don't, then you may place a coil across the feed line and accomplish the same thing. Coils you can wind yourself and they are less cumbersome than stubs and less prone to mechanical failure. Also, they cost nothing, you can wind them yourself with just a bit of wire and the pair of alligator clips you're already using at the top of your stub. Hang the coil right where you have hung the stub and it will do the same thing. Measure the stub with a DMM that has an inductance reading feature, and make a coil that is of matching inductance. Stick the thing in your pocket the next time you need that band go out and clip it on the line. I have one last comment, repeating from an earlier memorandum, with the use of a good swinging link coupler, I have never had the slightest difficulty matching any impedance from any antenna of any length or any length feed line. My tuner gave me a perfect 50 ohm resistive load without lumped constants or stubs at all times! Of course you will have to do some scrounging, perhaps even spend a little money, but for me, it was the most convenient answer. In my next memorandum I will discuss some reasons you might want to go through this process. VY 73, & "God Bless" DE TR