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#61




Yes, he died not long ago, within the last year I believe.
Roy Lewallen, W7EL Dr. Slick wrote: Roy Lewallen wrote in message ... I'd be one of the people arguing. Radiation resistance fits every definition of resistance. There's no rule that a resistance has to dissipate power. The late Mr. Carr was quite apparently confusing resistance with a resistor, a common mistake. BTW, did Joseph Carr really pass away? Sad, his book is very practical. Slick 
#62




Most simple derivations for the input impedance of a dipole assume it's
infinitely thin. The general problem of a dipole made from wire of finite diameter is a lot tougher, and is the topic of the papers by the authors I listed in another recent posting. With EZNEC, you'll find that the dipole impedance will continue to change as you make the wire diameter smaller and smaller, until it gets too small for the program to handle at all. Roy Lewallen, W7EL Tarmo Tammaru wrote: Kraus comes up with Z=73 + j42.5. He then goes on to say that an actual dipole is made a few % shorter, which yields 65 + j0. When I did an EZNEC calculation on a 1/2 wave dipole at 3MHz, I did not quite get that. For a #30 wire in free space I got 76.81 + j43.89 at 3 MHz, and 72.88 + j0.3465 at 2.94 MHz. I let EZNEC tell me what the wavelength was, and used 1/2 of that for the length of the dipole. Tam/WB2TT 
#63




"Tom Bruhns" wrote
"Reg Edwards" wrote I didn't say they were unimportant. I said they served only to add to the confusion when considering operation of the usual amateur installation when the generator internal resistance is unknown. Indeed, and not only that, the generator (ham transmitter) is commonly neither a linear system nor time invariant. Also, maximum power (conjugatematched load) from a linear generator is generally not the most efficient case. A great many generators and amplifiers are distincly NOT designed to deliver power to a matched load, but rather to deliver power efficiently to a specific load which is mismatched with respect to the output impedance of the generator/amplifier. There are times when knowing that a generator is a linear 50 ohm source (within some small tolerance) is importantI deal with them all the time in the work I dobut in a typical ham transmitter application, that's very seldom if ever the case. ==================================== Tom, To add a bit more  50ohm generators as used in laboratories (so that measured reflexion loss, mismatch loss etc, mean something) are effectively constant voltage generators in series with a 50ohms resistor, or constant current generators in shunt with a 50ohm resistor. They may be followed by an ampifier whose output impedance is held constant at 50ohms by some automatic means. None of these circuits bear much resemblance to a pair of 807's and a tuned tank. The best that can be said about Rg of the usual HF radio transmitter is that Rg is indeterminate. IT EVEN VARIES AS THE LOAD IMPEDANCE IS CHANGED which most of the Guru's contributing to this newsgroup appear to be unaware of or at least choose to disregard. So what does "adjusting RL to equal Rg" mean? To use it in a description of feeder + antenna behaviour further propagates myths, including those surrounding SWR, forward power, reflected power, SWR meters, etc. Does Terman ever bother to mention Rg of a Tx PA? If he doesn't it can't matter very much to him. The ARRL handbook, when numerically designing a transistor linear HF PA, makes no mention of Rg.  Reg, G4FGQ 
#64




Dr. Slick wrote:
"What`s the definition of "surge impedance" versus regular old "impedance"?" Arnold B. Bailey treats this better than anybody I`ve seen. But, there are many treatments. The regular old impedance of an antenna depends upon its termination. Surge impedance of an antenna depends on its conductor`s inductance per unit length and capacitance per unit length. In the antenna these are not uniform as they are in a transmission line, and average values have been found useful. Best regards, Richard Harrison, KB5WZI 
#65




On Thu, 17 Jul 2003 12:05:19 0700, Roy Lewallen
wrote: Most simple derivations for the input impedance of a dipole assume it's infinitely thin. The general problem of a dipole made from wire of finite diameter is a lot tougher, and is the topic of the papers by the authors I listed in another recent posting. With EZNEC, you'll find that the dipole impedance will continue to change as you make the wire diameter smaller and smaller, until it gets too small for the program to handle at all. Roy Lewallen, W7EL Hi All, The derivation of dipole electrical characteristics comes by neither thin nor thick (cylindrical) elements but through a simpler (conceptually, not mathematically) work described by S.A. Schelkunoff in "Advanced Antenna Theory," John Wiley and Sons, 1952. Schelkunoff approaches the design as merely the extension of the transmission line and he answers the issue of the antenna (the thin wire form) being nonlinear (the presumed incremental inductance/capacitance is not constant along the length of the split transmission line) by simply employing conical structures. The Biconical Dipole "develops a transverse spherical (TEM) wave analogous to that on a conventional transmission line" (reference "Antennas and Radiowave Propagation," Robert E. Collin, McGraw Hill, 1985). "Thus the biconical antenna theory provides a theoretical basis for assuming a sinusoidal current distribution on thinwire antennas." Like any transmission line terminated in its own character impedance, the Biconical Dipole (within limits imposed by size and apex angle) also presents a wide frequency range exhibiting a constant radiation resistance (about 160 Ohms across three octaves, by my margin notes). The easiest validation of this is found in the Discone. http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm 73's Richard Clark, KB7QHC 
#66




Schelkunoff's method is elegant, and one that lends itself to relatively
simple calculation  in closed form  with a computer. However, it doesn't give results which are in as good agreement with measurements than some other methods, so some assumptions made in his derivation aren't completely correct. A good summary of various methods and their validity appears in David Middleton and Ronold King, "The Thin Cylindrical Antenna: A Comparison of Theories", _Journal of Applied Physics_, Vol. 17, April, 1946. The program for calculation of the "Field Day Special" antenna (ftp://eznec.com/pub/fdsp~.exe) uses Schelkunoff's method, and it's perfectly adequate for the purpose. Of course, these days we can easily do very accurate calculations from very fundamental equations with a computer using the method of moments or other methods. There's a very good description of the method of moments in the second edition of Kraus' _Antennas_. I assume it's also in the third edition, which I don't yet have. Roy Lewallen, W7EL Richard Clark wrote: On Thu, 17 Jul 2003 12:05:19 0700, Roy Lewallen wrote: Most simple derivations for the input impedance of a dipole assume it's infinitely thin. The general problem of a dipole made from wire of finite diameter is a lot tougher, and is the topic of the papers by the authors I listed in another recent posting. With EZNEC, you'll find that the dipole impedance will continue to change as you make the wire diameter smaller and smaller, until it gets too small for the program to handle at all. Roy Lewallen, W7EL Hi All, The derivation of dipole electrical characteristics comes by neither thin nor thick (cylindrical) elements but through a simpler (conceptually, not mathematically) work described by S.A. Schelkunoff in "Advanced Antenna Theory," John Wiley and Sons, 1952. Schelkunoff approaches the design as merely the extension of the transmission line and he answers the issue of the antenna (the thin wire form) being nonlinear (the presumed incremental inductance/capacitance is not constant along the length of the split transmission line) by simply employing conical structures. The Biconical Dipole "develops a transverse spherical (TEM) wave analogous to that on a conventional transmission line" (reference "Antennas and Radiowave Propagation," Robert E. Collin, McGraw Hill, 1985). "Thus the biconical antenna theory provides a theoretical basis for assuming a sinusoidal current distribution on thinwire antennas." Like any transmission line terminated in its own character impedance, the Biconical Dipole (within limits imposed by size and apex angle) also presents a wide frequency range exhibiting a constant radiation resistance (about 160 Ohms across three octaves, by my margin notes). The easiest validation of this is found in the Discone. http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm 73's Richard Clark, KB7QHC 
#67




I referred to Terman as "him".
It should, of course, have been "HIM". ;o)  Reg. 
#68




William E. Sabin wrote:
If the transmitter output is 100 W and the reflected power is 3 W, then the 100 W is the difference between 100+3=103 W (forward power) and 3 W (reflected power). If the source is a signal generator equipped with a circulator and load, the generator is putting out 103 watts, and the circulator load is dissipating 3 watts, is the generator still only putting out 100 watts by definition?  73, Cecil, W5DXP 
#69




On Thu, 17 Jul 2003 17:12:33 GMT, Richard Clark
wrote: On Thu, 17 Jul 2003 17:00:55 GMT, Dilon Earl wrote: If I have a 100 watt transmitter and my wattmeter shows 3 watts reflected. Is 3 watts actually being dissipated in the tank and final PA? Hi Dilon, Does it become 3 watts hotter under the same drive conditions without the reflected power? You would be surprised how few pundits actually discuss this in these terms. Of course everyone would be surprised if anyone attempted to perform this chore. I like to include this jab at those who rave on about the impossibility of knowing the internal resistance of a transmitter and are satisfied to squeak out 100W RF for 250W DC in. 73's Richard Clark, KB7QHC Richard; I'm not sure if it does get 3 watts hotter. I was always under the impression that operating a transmitter with a high reflected power was unhealthy for my PA. 
#70




On Thu, 17 Jul 2003 14:42:37 0700, W5DXP
wrote: William E. Sabin wrote: If the transmitter output is 100 W and the reflected power is 3 W, then the 100 W is the difference between 100+3=103 W (forward power) and 3 W (reflected power). If the source is a signal generator equipped with a circulator and load, the generator is putting out 103 watts, and the circulator load is dissipating 3 watts, is the generator still only putting out 100 watts by definition? No, you just said it was putting 103 watts.. :) Was that the right answer? 
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