Stop and think about this for a minute. What you want to do is move power from one place to another without too much loss and then radiate as much of that power as has been moved to the antenna. The first part, that transferring/moving of power, deals with matching impedances, SWR. The second part, the most efficient radiation of that power deals with resonance of the antenna. (Resonance is defined as the absence of reactance, a part of impedance along with resistance.)
There are some 'catches' with doing all of that. One of those catches is that an SWR meter has no idea what reactance is, it can't measure it all alone, it can only measure the combination of reactance AND resistance which is called impedance. That's not good because there are a huge number of combinations of that 'R' and 'X' (reactance) that will display as a 1:1 on an SWR meter. [The biggy about reactance is that it doesn't 'radiate' or contribute to the radiation of anything! It's a dead loss.]
Another one of those 'catches' is that an SWR meter can only compare the impedances between two point, the one in 'front' of it and the one 'behind' it. So when that meter is placed at the transmitter end of a feed line it's measuring the impedance match between the transmitter's output jack and the -whole- antenna system, feed line AND antenna combined. That can't tell you anything about any mismatches between feed line and antenna. That means that there could be a large amount of power loss at the antenna's feed point because of the antenna isn't the same impedance as the feed line. The antenna -system- as a whole may look good to that meter at the transmitter end of the system but it doesn't have to be 'good' at all, it could be terrible at the antenna end.
Here's another fact that you aren't going to like. The input impedance of almost every -resonant- antenna is not going to be 50 ohms, or even close to it in most cases. The input impedance of a 1/4 wave vertical antenna isn't 50 ohms, it's closer to around 25 or 30 ohms impedance. That means that in the absolute best case, resonant antenna and a feed line of 50 ohms, the -normal- SWR would be something between 1.5:1 and 2:1. That means that to do it 'right', any impedance matching has to be done right there, at the feed point of that 1/4 wave antenna if you want to get the most out of it. Nasty thought, huh? Sorry, that's the way it is.
{Ever wonder why beams almost always have some kind of matching device, gamma, beta, hair-pin match at the feed point? It's for exactly the same reason.}
I'm tired of typing so am going to end it right here. None of this is 'new' at all. It's been around forever. People tend to loose sight of it because no one seems to 'do it' that way. The results may be 'acceptable', but it certainly isn't the best. There are two things that have to be done with all antenna systems. Make'em resonant and a good impedance match. Don't concentrate on one at the expense of the other.
- 'Doc
There are some 'catches' with doing all of that. One of those catches is that an SWR meter has no idea what reactance is, it can't measure it all alone, it can only measure the combination of reactance AND resistance which is called impedance. That's not good because there are a huge number of combinations of that 'R' and 'X' (reactance) that will display as a 1:1 on an SWR meter. [The biggy about reactance is that it doesn't 'radiate' or contribute to the radiation of anything! It's a dead loss.]
Another one of those 'catches' is that an SWR meter can only compare the impedances between two point, the one in 'front' of it and the one 'behind' it. So when that meter is placed at the transmitter end of a feed line it's measuring the impedance match between the transmitter's output jack and the -whole- antenna system, feed line AND antenna combined. That can't tell you anything about any mismatches between feed line and antenna. That means that there could be a large amount of power loss at the antenna's feed point because of the antenna isn't the same impedance as the feed line. The antenna -system- as a whole may look good to that meter at the transmitter end of the system but it doesn't have to be 'good' at all, it could be terrible at the antenna end.
Here's another fact that you aren't going to like. The input impedance of almost every -resonant- antenna is not going to be 50 ohms, or even close to it in most cases. The input impedance of a 1/4 wave vertical antenna isn't 50 ohms, it's closer to around 25 or 30 ohms impedance. That means that in the absolute best case, resonant antenna and a feed line of 50 ohms, the -normal- SWR would be something between 1.5:1 and 2:1. That means that to do it 'right', any impedance matching has to be done right there, at the feed point of that 1/4 wave antenna if you want to get the most out of it. Nasty thought, huh? Sorry, that's the way it is.
{Ever wonder why beams almost always have some kind of matching device, gamma, beta, hair-pin match at the feed point? It's for exactly the same reason.}
I'm tired of typing so am going to end it right here. None of this is 'new' at all. It's been around forever. People tend to loose sight of it because no one seems to 'do it' that way. The results may be 'acceptable', but it certainly isn't the best. There are two things that have to be done with all antenna systems. Make'em resonant and a good impedance match. Don't concentrate on one at the expense of the other.
- 'Doc
