Thank you Al for this wonderful clarification! Yes the thread started because someone was concerned that the AX1 was a poor performer because it was non resonant,or resonant at frequencies outside the intended bands. And that using a tuner would decrease the efficiency. Of course it is a compromise antenna for various reasons,but not due to being non resonant or requiring a tuner to match it to the 50 ohm input of the radio. And also thanks for the statement about open wire lines for SWR and picking up noise-a common myth. It’s unfortunate that a rather prominent speaker/youtuber/columnist has little understanding of the benefits of open wire lines over coax. Dan Presley 503-701-3871 danpresley@me. com
> On Oct 23, 2024, at 12:11, Al Lorona <[email protected]> wrote: > > Here's a true statement: If an antenna is resonant, it radiates no better > and no worse than a similar-sized antenna that isn't resonant. > > First, let's define what 'resonance' is. Remember how impedance Z consists of > a resistive part and a reactive part? We usually write it like this: > > Z = 14 - j80 > > where Z = impedance > resistance R = 14 ohms, and > reactance X = 80 ohms (which in this case is capacitive because of > the negative sign) > > 'Resonance' simply means that the reactive part is zero (0). The resistance > can be any value, but if the reactance is zero, that's a resonant system. So > this: > > 14 - j0 > > represents a resonant system. > > It turns out that whether your antenna Z = 14 - j80, or if your antenna Z = > 14 - j0, the resulting radiation is the same. I'm assuming that there's > probably a network somewhere in the system to match each of these impedances > to 50 ohms. > > An antenna doesn't have to be resonant. But if it happens to be resonant, it > won't radiate any better or worse than if it weren't. Resonant and > non-resonant antennas can radiate equally well. > > You might say, "Well, I choose *not* to use an antenna matching network, so > I'd rather my antenna be resonant, because that'll result in the lowest SWR." > > Yes, but in the case above where the antenna was resonant, the SWR is still > 3.57 to 1, so you would probably want to use a matching network of some kind. > That doesn't necessarily mean an antenna tuner... you could have a balun, a > quarter-wave matching section, a trap, a coil, a capacitor or capacitors, a > transformer, a particular length of transmission line, something like a delta > feed or a gamma match, a stub, a resistor, or something else. > > The thing that got me thinking about this was a thread where somebody was > bothered that their AX1 antenna (or whatever it's called) wasn't resonant. Or > maybe you avoid some other antenna because it's 'not resonant'. Just realize > that whether the AX1 is resonant (reactive part equals zero) or whether it's > not, it'll radiate the same. > > Resonance is the magic that everyone is chasing, even though it doesn't buy > you all that much. I'll always remember my dad saying, "I'll tell you how > long to make your antenna: long enough to reach from where it begins to where > it ends." He understood the relative unimportance of resonance. > > Rhombics are non-resonant antennas, but boy do they radiate beautifully. > Similarly, any other antenna that's not resonant can be made to behave > beautifully, sometimes by using a matching network or antenna tuner or > whatever. > > "But I use one of those other methods you just mentioned, instead of an > antenna tuner which has lots of loss." Careful, your matching device(s) could > have just as much loss as plain old, properly sized capacitors and inductors. > > "But I hate twiddling knobs." Okay, that's fine. Do what you have to do, but > just don't claim that your 'resonant' antenna is any better than my > 'non-resonant' antenna. > > "But if the antenna's non-resonant, the SWR's probably gonna be higher, and > that means more loss in the transmission line." So use open-wire line. > > "But if I use open-wire line, I'm going to pick up more noise." Not > necessarily. > > "But, but,..." > > > Al W6LX/4 > > P. S. It's actually a false statement that resonance always results in the > lowest loss with a given transmission line. We pretended it was true so we > could make our point. > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
