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SSB Antenna theory
I guess I'll pick up the latest Antenna Handbook and start reading.
Doug, k3qt s/v Callista "Gary Schafer" wrote in message ... I am not sure just what you are missing here. Or maybe I am not understanding your question. Again I am posting the reference pages below in the antenna handbook. Not once could I find in there that they stated that a loading coil on an antenna made it into a quarter wave antenna as did earlier versions of the antenna handbook and the regular handbook. That is why I say they finally got it right. Maybe you are questioning which one is right. In the earlier handbooks the subject was more or less glossed over with poor explanation of what happens in the antenna matching. The newer antenna handbook goes into more detail. I even tell you the pages! Also if you look at my earlier post "Notes on short SSB antennas" there is a link to W8JI's web site where he discusses the same stuff that I have. He tells you why a loaded antenna is still the same length electrically as an unloaded antenna. In that post there is a copy of part of his article that deals with this topic as I credited him with. For more details look at his web site. REFERENCE 1 If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. REFERENCE 2 Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. Regards Gary On Fri, 30 Apr 2004 17:51:34 -0400, "Doug Dotson" wrote: Gary, I'm not trying to be contrary at all. So much of what floats around on this and other forums is totally anecdotal. When it comes to electrical engineering I expect a more formal and verifiable approach. More below. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I take it that you are trying to learn and not just be argumentative. Absolutely. I'm tired of this argument. I'd like to be up to date in the current school of thought. Kind of like that myth that you need to line your hull with yards of copper foil as a counterpoise when emperical evedence says otherwise. If you read what I wrote, I said that in the antenna handbook that they finally have it right. But the only reference you cite is the ARRL Antenna Handbook. When you say they finally got it right, you must base that on something other than the handbook itself. When you said they were wrong for so many years, you gave no reference that supports that view. When you say they finally got it right you still gave no reference to support that suposition. So what it boils down to is that the handbook used to be wrong, now is right, and you are the judge as to what was right and wrong with no independently verifiable refererence to either position. I expect this from the government, but I cannot accept if from someone that appears have a reasonable engineering background. Read the first three paragraphs under "TUNING TO A QUARTER WAVE" below. I have read it. No reference other than the ARRL itself which used to be wrong and now is right. Regards Gary On Fri, 30 Apr 2004 00:07:54 -0400, "Doug Dotson" wrote: First you cite several instances that the ARRL treatment is wrong. Then you say the they finally got it right. Where are your references that substantiate either statement? Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . I tried to give an abbreviated synopsis of the subject and dispel some myths. I did not cover all the details. You need look no further than the ARRL itself for references. If you read the whole post you would see that near the bottom I credited the ARRL 2000 edition of their handbook, antenna section. The definition of "radiation resistance" is from there and the calculations of the example antenna with impedance's and voltages developed are directly from there. If you also look in the 18th edition 1997? of the ARRL antenna handbook chapter 16 "mobile and marine antennas", and probably later versions, you will see where they properly discuss loaded short antennas and what the coil does. Also if you look at the earlier post titled "Notes on short SSB antennas" you will find a reference to W8JI's web site where he discusses these very items in detail. He and many other engineers will tell you the same thing. I don't mean to discredit the ARRL but their statements in regard to tuning an antenna to a quarter wave in their older publications are misleading as evidenced by all the misconceptions that fly around. While that is a simplified explanation of what happens with the antenna matching, I suppose it was easier to propagate that (no pun intended) term for simplicity. But if you really want to understand what is going on it will get you into trouble in understanding as it is a conflict with what really happens. Regards Gary On Thu, 29 Apr 2004 20:25:53 -0400, "Doug Dotson" wrote: So, is this something you put together? How about some references? ARRL is a pretty reputable outfit. If you are going to dispute their writings, you should provide some some verifiable references. Doug, k3qt s/v Callista "Gary Schafer" wrote in message .. . This tries to explain how short SSB antennas operate and why. The discussion is concerning antennas that are shorter than a quarter wavelength. TUNING TO A QUARTER WAVE I looked through several older handbooks and antenna handbooks and found most of them professing what Larry is saying about "tuning an antenna to an electrical quarter wave." No wonder so many people have it wrong! The ARRL has been preaching this stuff for years. But in the same paragraphs they will speak to the "electrical length being very close to the physical length". Can't have it both ways! Even the 2000 ARRL handbook has it wrong. They finally got it right in their antenna handbook. Not once did I see reference to "tuning an antenna to an electrical quarter wave length. It may seem like semantics but there are a lot of people that get confused and think that when making the system resonant with a shorter antenna that the antenna is really the same as a quarter wave length antenna when there is a loading coil. It is far from that. Its radiation resistance and its feed point resistance are both much lower. An antennas electrical length is what it is by itself. Adding a coil to it to make it resonant will not change that. |
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SSB Antenna theory
"Doug Dotson" wrote ... I guess I'll pick up the latest Antenna Handbook and start reading. Doug, k3qt s/v Callista The fundamental work on "small" antennas was done by a guy named Wheeler. After digging in the filing cabinet I found his paper from the proceedings of the I.R.E. (institute of radio engineers?) that preceded the IEEE. "Fundamental Limitations of Small Antennas" by Harold A. Wheeler fellow, I.R.E. December 1947 One insight is that a small antenna can theoretically be nearly as efficient as a 1/4 wave element but it is difficult to match to the small radiation resistance. (actually you match to the sum of the radiation and loss resistance). The efficiency is simply the ratio of radiation resistance to the sum of radiation plus loss resistance. A small loop antenna which looks inductive makes the job easier as you can build a low resistance loop and use high Q capacitors for tuning/matching. regards, -rick- |
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SSB Antenna theory
"-rick-" wrote in
: "Doug Dotson" wrote ... I guess I'll pick up the latest Antenna Handbook and start reading. Doug, k3qt s/v Callista The fundamental work on "small" antennas was done by a guy named Wheeler. After digging in the filing cabinet I found his paper from the proceedings of the I.R.E. (institute of radio engineers?) that preceded the IEEE. "Fundamental Limitations of Small Antennas" by Harold A. Wheeler fellow, I.R.E. December 1947 One insight is that a small antenna can theoretically be nearly as efficient as a 1/4 wave element but it is difficult to match to the small radiation resistance. (actually you match to the sum of the radiation and loss resistance). The efficiency is simply the ratio of radiation resistance to the sum of radiation plus loss resistance. A small loop antenna which looks inductive makes the job easier as you can build a low resistance loop and use high Q capacitors for tuning/matching. regards, -rick- In 1947, matching the very low impedance feedpoint of a loaded vertical antenna was a problem. But, after the invention of the broadband iron powder toroids that are very efficient, magnetically at high frequencies, it's not much of a problem at all. At the base of my monster 1.8-30 Mhz 15' mobile ham antenna (4' ss base, 6" diameter monster loading coil, 3' mast, 36" capacitor hat and stainless whip on top cut so that shorting the whole coil resonates it at 14.250 Mhz) is a T-200-2 powered iron toroid core wrapped with insulating fiberglass tape and 12 turns of bare #10 copper. The core is mounted in a plastic construction box between the posts of banana jacks that are soldered to the outside of each turn so banana plugs can select the turns ratio. One end of the coil is connected to "ground", the chassis of the car. Any reasonable RF grounding system would hook there on a boat. The coax from the transceiver's 650 watt, 12V linear amp is terminated with a banana plug to select the input tap, and a short length of braided strap goes between a banana plug and the bottom feed point of the antenna for the output tap. Best match occurs when the lowest reflected power occurs on the SWR meter of the linear amp (or transceiver with the linear out of the circuit). On my antenna, on the 3.5-4 Mhz ham band for instance, the input tap is across the entire 12 turns and the antenna is tapped 4 turns above the ground point. SWR at resonance is perfect, 1:1, and large corona arcs occur at the top of the whip tip and bent around ends of the 8 spokes of the 36" capacitor hat, made of stainless welding rod welded to two large flatwashers at the center. Signals are very comparible to any fixed station here running the same power. Cars passing blow horns and shout, "Your Antenna Is On Fire!", out their windows. It will light up a flourescent tube in your hand at 10' away, easily. The square of the turns ratio is 9:1 so the antenna's impedance is somewhere around 6 ohms or so at the feedpoint. The 650 W amp melted the solder joints on the core using #12 wire for the turns, so I went to #10 which is about as thick as I can go with 12 evenly spaced turns without shorts. #10 wire gets too hot to touch, but doesn't melt solder any more...(c; A second similar toroid autotransformer is mounted in another box with 24 turns of #12 next to the first. It is used for the 160 Meter band (1.8-2 Mhz). A second loading coil on top of the first (3" diam, 200T) adds sufficient inductance to tune the 15' antenna down to 1.8 Mhz, but at 650 watts there is so much corona arcing it makes the SWR readings go crazy so power is reduced to 300W or whatever the humidity around the antenna can stand at that particular moment. If one were to forego the old untuned wire/tuner marine antenna configuration and go with a real tuned vertical, this toroid autotransformer will very efficiently match the very low base impedance to the 50 ohm transceiver across the 2-30 Mhz HF band. The car's electrical wiring resonates around 3.9 Mhz, causing all the dash lights to glow brightly with SSB modulation on their own, to the amazement of even ham radio passengers. Thank God old Mercedes 220D diesels have no electronics in them! Many hams have gone to a remotely-tuned mobile antenna that uses a powered motor to move the tap on a center loading coil. Here's what it looks like: http://www.qth.com/n7lyy/about.html It uses a screwdriver DC motor to move the loading coil up and down against a large contactor and will tune the entire band. If a boater were to make the whip longer than the 66" limit for cars, it would be even more efficient with less coil turns below 12 Mhz. 66" is so it will tune 29.7 Mhz, the highest HF ham band boaters don't need. This antenna system would easily mount on a stern rail, using the rail as groundplane if it were all connected together, and would tune from the radio while watching the SWR meter on the radio (or output power meter which would just tune for maximum output power). Larry W4CSC Some day I might try this antenna using the handrails of the boat as ground plane. It's gotta work better than the stupid untuned backstay and inefficient antenna tuner. It certainly results in much better signal reports. |
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SSB Antenna theory
On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC
wrote: The square of the turns ratio is 9:1 so the antenna's impedance is somewhere around 6 ohms or so at the feedpoint. The 650 W amp melted the solder joints on the core using #12 wire for the turns, so I went to #10 If one were to forego the old untuned wire/tuner marine antenna configuration and go with a real tuned vertical, this toroid autotransformer will very efficiently match the very low base impedance to the 50 ohm transceiver across the 2-30 Mhz HF band. Larry W4CSC Some day I might try this antenna using the handrails of the boat as ground plane. It's gotta work better than the stupid untuned backstay and inefficient antenna tuner. It certainly results in much better signal reports. Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary |
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SSB Antenna theory
Gary Schafer wrote in
: On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? |
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SSB Antenna theory
On Tue, 04 May 2004 21:15:40 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? Heh heh, still haven't figured it out Larry? Regards Gary |
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SSB Antenna theory
On Tue, 04 May 2004 21:15:40 -0000, Larry W4CSC
wrote: Gary Schafer wrote in : On Tue, 04 May 2004 15:08:08 -0000, Larry W4CSC wrote: Your feed point resistance may be 6 ohms but about 5.8 to 5.9 ohms of that are coil resistance. The radiation resistance of the 15 foot whip on 3.5 mhz is in the order of .1 ohm. So about 97% of your power is going up in heat in the coils. Only a couple percent of the power is making it to the antenna to be radiated. Of 650 watts only around 20 watts makes it to the antenna. A full quarter wave length vertical has a radiation and feed point resistance of around 36 ohms. Much easier to get power into than a .1 ohm 15 foot antenna. Oh, don't forget to add in all the ground loss resistance too. Less power to the antenna yet. If you can get your feed point resistance down to around 1 ohm then you will get about 10% of your power into the 15 foot antenna! Regards Gary I've never met anyone so full of pure bull**** in my entire life as you, Gary. It's simply incredible. One hopes noone in their right mind will hire you as an engineer and suffer the consequences. I doubt 20 watts would make a signal 800 miles away at 20 over S9 in any conditions, but we're, I'm sure, gonna hear more bull**** from you about it in the near future. Larry W4CSC What class licenses and degrees do you hold, anyways? I've been a 1st phone licensee since the 1960's, an avid ham operator since 1957 when I was 10 and graduated with honors from many military electronics schools run by the US Navy because Vietnam's draft kinda got in the way of college in 1964. Stop by some time and I'll let 20 watts burn your ass for you....(c; I've never seen 20 watts produce a corona in air over 8" long.... How many kilovolts is that in air at sea level? What part do you deem to be "bull****" Larry? The parts you don't understand? I know that you like sensationalism in big arcs and bragging rights of running high power. That's fine if that's your thing but you let it cloud reality. Being able to pull a big arc from an antenna tells you nothing about its efficiency or how well it will radiate. It does make for good show though. A tesla coil will produce some pretty high voltage and corona too. By the way, time in grade doesn't count either. Being a corporal for 20 years doesn't automatically make one an expert at anything. Not that you can't be an expert, time in grade just doesn't contribute. Note that I haven't said that you are full of bull****. I am giving you the benefit of the doubt. If you went to tech school as you claim, you have forgotten some of the basics or you were asleep through many parts. I would have thought that basic AC circuit theory would have been part of your education. Maybe not. If you are interested in how this stuff really works it might help us to understand some of the things that you have misconceptions about. Here are a few questions: 1. Do you understand that when you have a capacitor and a coil in series in an AC circuit that the voltage across either can be much greater than the applied voltage to the circuit? (basic AC theory) 2. Do you understand that a coil has series resistance as well as reactance? 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! 4. Do you know that Radiation resistance is in series with feed point resistance. 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. 8. Do you understand that the radiation resistance gets very low in a short antenna? If you do not understand any of the above questions please let us know. That may be the reason that you are not understanding what goes on in your antenna system. What I previously wrote pertaining to the voltage developed across the coil and how low the radiation resistance can be on a short antenna was quoted directly from the 2000 ARRL handbook. If you have it look at HF mobile antennas. Page 20.46, 3rd column on the page. It explains why the voltage is 5000 volts rms across the coil with just 100 watts applied to an antenna with a radiation resistance of less than an ohm. Isn't that amazing! Must be black magic huh Larry? Or just maybe it has something to do with the above questions. Regards Gary |
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SSB Antenna theory
I'm gonna jump in here -- not as an expert on antennas, but merely as someone who understands maxwell's equations and some mathematics. On 2004-05-05, Gary Schafer wrote: If you are interested in how this stuff really works it might help us to understand some of the things that you have misconceptions about. I don't think that it'll help at all to know what (if anything) he has misconceptions about. But it *would* help to have a mathematical model and a definition of terms. OK. Gary says that "your history doesn't matter; it doesn't matter what tech school you went to, etc.", and I agree to some extent. Since I didn't go to any tech school, I've got nothing to be embarassed about. I just happen to know a bit of math and physics. Here are a few questions: 2. Do you understand that a coil has series resistance as well as reactance? Wow. That's interesting. I'm just going to take a shot in the dark and assume that by "series resistance" you mean if I apply a DC voltage across the coil, and wait until the circuit reaches a steady state, I'll notice some current flowing; the ratio of the voltage applied to the steady-state current flow is what I call "series resistance." [...and you're implicitly asserting that this ratio is independent of the voltage applied, i.e., that the steady state current is linear as a function of the applied voltage"...] I expect that this assertion is true. So in other words, what you're calling "series resistance" is the real part of the (complex number) impedance, and reactance is the imaginary part. From what I've seen Larry write, I'll bet he understands that. 3. Do you understand the difference between Radiation resistance and feed point resistance? This is an important one! I'm just a farmer from the country, but where I come from, there's just impedance. I don't know how you split the real part of that complex number into two parts. Maybe where you come from, there's "carbon resistor" resistance and "thin-film" resistance, too, but I'm not sure how the electrons can tell the difference. A Google search doesn't yield any real information on "feed point resistance," so I guess that answering for myself, I can say "sure...radiation resistance is the real part of the impedance of an antenna; feed point resistance is an undefined term." There *does* seem to be widespread use of the term "feedpoint resistance," although definitions seem to be scarce as hen's teeth. Just being the ignorant sorta guy I am, I tend to gravitate towards the ones that define "feedpoint impedance;" one could then say that feedpoint resistance is the real part of that complex impedance. But that seems strikingly similar to the definition of "radiation resistance." How very odd. 4. Do you know that Radiation resistance is in series with feed point resistance. Ah...now you're losing me. For me, one of those terms is undefined, so it's hard to be "in series with" the other. And if we take "feed point" to be "feedpoint," then since the two seem to be the same, it's hard to admit that they're in series. But I'm sure you can clear this up for me. Can you just write down the equations? (with all the symbols defined -- that'll make it much clearer). 5. Do you know that the same amount of current that flows at the feed point of the antenna is the same amount that flows in the radiation resistance of the antenna? They are in series you know. "Flows in the radiation resistance?" I don't honestly know whether Larry knows more or less than you do, but at least I've never seen him write something like this. 6. I assume that you know ohms law and that if the same amount of current flows in two series resistors that the larger resistance will dissipate more power than the lower value resistor? Um...Ohm's law tells me, if I recall correctly, that for certain materials, the current flowing through them varies linearly with the applied (DC) voltage; in these cases, the ratio of the two is called the "resistance." If you think I'm being overly pedantic here, you can ask "what's the resistance of a diode?" The answer is, of course, "the current through a diode does not vary linearly as a function of the applied voltage, so it does not have a resistance." So you have to be careful about applying Ohm's law... 7. Do you understand that there is a phase shift between current and voltage across a coil in an AC circuit. I would say "an inductor has a complex impedance that happens not to be a real number, but rather one that has an imaginary part as well." 8. Do you understand that the radiation resistance gets very low in a short antenna? Uh...I guess I don't "understand" that. But if you'd write out an equation or two, I might know what you meant by it. ---------------------------------------------------------- Someone else asked a very interesting question earlier: 1. You state that some editions of some ARRL publication are wrong. 2. You state that other editions are right. You haven't told us where one finds evidence for this wrongness/correctness. Does one of them have an error in some equation? Can you construct a real circuit for which the predictions of one book are wrong and the predictions of the other are correct? Or do we just have to take your word for it that one is right, the other wrong? If it's the latter, then why bring the ARRL into it? Why don't we just agree that whatever you say is right, and whatever anyone says that appears to contradict it is wrong? It'd save a lot of writing... statement about antennas paraphrasing ARRL ahndbook deleted Isn't that amazing! Must be black magic huh Larry? Or just maybe it has something to do with the above questions. Maybe...but I'd find it more compelling if it had something to do with known (by which I mean "widely accepted and tested") physical laws like Maxwell's equations, and an analysis of the circuits in question. --John Hughes |
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SSB Antenna theory
"Larry W4CSC" wrote
I've never seen 20 watts produce a corona in air over 8" long.... Awww .... my buddy's 4-watt CB does it all the time. Of course he had it peaked up at the truck stop but ... (c; 73, K3DWW |
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SSB Antenna theory
"Vito" wrote in
: "Larry W4CSC" wrote I've never seen 20 watts produce a corona in air over 8" long.... Awww .... my buddy's 4-watt CB does it all the time. Of course he had it peaked up at the truck stop but ... (c; 73, K3DWW FINALLY, someone in this thread with some common sense....(c; 73, larry W4CSC |
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