Hmmm, TMC TAC1 tuner specifies 80% efficiency. So at least in this case, 20% is lost. ftp://bama.edebris.com/bama/tmc/tac1/pages/tac1_04.jpg
Apparently it gets worse as the frequency climbs up beyond 18 Mc I suspect the same is true for the johnson boxes that also use air coils. de KA4JVY Mark > FALSE STATEMENT #3 --- Tuners waste a lot of power and just make the > transmitter think the antenna is right. > TRUE STATEMENT --- A tuner consists of coils and capacitors neither of > which by mathematical definition consumes energy. The adjustments of > the coils and capacitors change the phase as well as the voltage to > current ratios of input and output. The slight amount of energy that > may be consumed by tuners is generally so negligible that it is very > difficult to measure. In some cases a tuners components maybe made of > poor quality material and too small for the job. These types of > components will get hot. Heat is an obvious point of loss. I had a > small MFJ tuner that was manufactured some years ago. It was just a > small external Pi-Net device and I found it to have a measurable > insertion loss. It turned out to be the rivets that held the connectors > on the little chassis. I soldered braid across the connectors to the > chassis and then the loss was then immeasurable. > > Modern solid state equipment is designed to work into a 50 ohm non > reactive load. Connecting a dummy load of 60 ohms instead of 50 ohms > will cause the rig to put out less RF current and make the automatic > drive level circuitry start pulling back on drive prematurely. If the > load becomes slightly reactive as well then the RF production will > decrease rapidly. A tuner is nearly a must for these rigs. > > In tube type XMTRs the use of toroidal transformers for the output is > impossible because of the high output Z of tubes. These rigs used > instead a Pi-NET or link coupled tuned circuitry to do the job of > matching the tube to the low impedance output. This type of circuitry > could match a relatively wide range of impedances from 25 ohms to > several hundred ohms as well as compensate for some reactance. Because > of this an external tuner may not have been necessary especially if > confined to one band on one antenna. A lot of folks put up multiple > antennas one for each band or used a multiband trapped dipole or some > other multiband radiator with a single coaxial down line. The Pi-Net in > the rig did all the compensation for them. But with solid state rigs > and no internal tuning it would be an near necessity to have an external > tuner if nothing more than a small PI-Net tuner such as the one I had > from MFJ > > > > Having to do with the conservation of energy laws. Here are some facts. > > 1. High quality capacitors (especially air or vacuum type with good > aluminum plates) have little or no measurable loss. They give almost > 100% of the energy they absorb back to the load or source. They are > adjusted with the inductors so as to send the energy to the load and not > the source. > > 2. Air inductors are also almost lossless except for a small amount due > to the resistance of the material. The energy they absorb is stored > magnetically and almost all given back to the load or source. They also > are adjusted with the capacitors so as to send the energy to the load > and not the source. > > 3. Antenna systems (including tuners) are made of material that is very > low in resistance to electron flow (or they should be). > > With the above facts in mind, consider the following scenario. > > 1. A transmitter is connected to an antenna system made with quality > components > > 2. The finals are not dissipating any more heat than they would if > connected to a perfect dummy load. > > 3. There is no measurable heat dissipated in any of the components of > the antenna system. > > Then the energy that is produced from the finals must be being > used by something irregardless of resonance. The energy must be going > to out into space because nothing is dissipating any heat that we can > measure and it makes no difference what length the antenna is because th > tuner is compensating for the reactance and transforming the current to > voltage ratios as needed to get the energy out. > > It is being radiated, hence the term "radiation resistance". > > Most folks mistakenly think of the term radiation resistance as > a fixed value of 73 Ohms. BUT THIS IS NOT TRUE. 73 Ohms is the > radiation resistance of a center fed 1/2 wave dipole in free space and > by the way increasing the size of the wire has very little effect on it. > A center fed full wave dipole will radiate the same amount of energy but > has a much higher radiation resistance. It has no greater or less > radiation efficiency than does the 1/2 wave dipole (negligible copper > resistance loss). It just radiates in a slightly different pattern. > > Theoretical, (neglecting copper losses) if all of the energy of > the radiated signal could be recaptured and measured from each of the > two antennas the measured amounts would be equal. > > > > Here is some question that I have never learned the answer to. > > I have never seen a value of radiation resistance assigned to a > center fed full wave dipole. Perhaps it is too difficult to measure? > As Don,K4KYV pointed out, "There has to be some current flow there, else > there would be no power transferred" > > I would also like to know the theoretical feed point resistance > of a theoretically infinite length dipole and why a rhombic is > terminated with a 600 ohm resistor instead of, for the sake of argument, > say a 100 Ohm resistor or some other value. > > I understand that Rhombic and long wires (10 wave lengths or > more) radiate 90% of there energy before the signal reaches the end of > the wires. And that the terminating resistor is there to lower > reflections that might make the antennas bi-directional. So could that > mean that 600 ohms is about the Radiation resistance of a infinite > length of wire? > > > Here is a little tidbit that may not be well known. > > Don, K4KYV, once explained to me, the reason for the 300 ohm > feed point of the folded dipole. It went like this. > > There or two wires which must divide there current evenly. > > Consider a 100 watt carrier gong into a 1/2 wave dipole. > > With the 73 ohm radiation resistance the current at the feed point would > be about 1.17 Amps and the voltage would be 85.4 Volts > > If another wire is added to make the antenna into a folded dipole then > each wire would have a current at the center of (1.17 / 2) or .585 Amps. > > But since only one wire is fed then in order to get the 100 watt value > the voltage must be double to 170.8 volts. > > R = E/I so 170.8 volts divided by .585 Amps equals about 292 Ohms. > Hence the value rounded to 300 Ohms. > > It is some what like an impedance ratio of 1:4 for a 2 wire folded > dipole. > > In a 3 wire folded dipole the currents will be divided by thirds per > wire. This will work out to near 600 Ohms for a 3 wire folded dipole. > > > > > > > ********************************************************************** > > > -----Original Message--Edited for space--- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Gary Schafer > Sent: Sunday, April 23, 2006 11:49 AM > To: 'Discussion of AM Radio' > Subject: RE: [AMRadio] antenna tuners > > > When using an antenna tuner and we tune the reactance out of the circuit > so > we only see a resistive component we can say it is resonant. But what is > really resonant? The antenna is not, the feed line is not, the tuner is > not. > > > The only thing resonance means in this case is that the capacitive and > inductive reactances at the tuner are equal. It confuses many people. > > 73 > Gary K4FMX > > > > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > > ______________________________________________________________ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:[email protected] > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami, Paul Courson/wa3vjb > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
