-2

In a youtube video titled "Antenna Engineer Vs Ham Radio Myths! True or False?" the guy says this in the comments:

The idea that a non resonant antenna cannot accept current as well as a resonant antenna is a myth. Of course you have to use a tuner with a non resonant antenna.

I highly doubt that, am I wrong to say this guy is full of it?

Marcus Müller
  • 15,910
  • 23
  • 45
K3ZD
  • 1
  • 1
    But the tuner is bringing the 'rest' of the system into resonance with the antenna. And, as easily, you can use a tuner to mess up the system by detuning it. Seems an argument over semantics. And that huge, bolded text is hard on the eyes. – Jon Custer Mar 28 '24 at 12:29
  • 1
    Even if it is a myth, that current isn't being used to do useful work. Unless warming the air around your shack or antenna is useful to you. However, it's hard to know what someone is referring to in a random YT comment. I mean, amateur and enthusiast simplifications aside, this stuff is well studied and the theory and practice mesh very well. Any one of us these days can get good SWR estimates and make Smith (or Smith-hyphenate) charts to be proud of. – clvrmnky Mar 28 '24 at 14:29
  • Previous Q&A of interest: https://ham.stackexchange.com/q/2482/26657, https://ham.stackexchange.com/q/16812/26657, https://ham.stackexchange.com/q/15793/26657 – clvrmnky Mar 28 '24 at 14:38
  • yes, you are wrong to say "the guy is full of it", but in a first approach mostly because it makes you sound arrogant! You could ask whether the guy is wrong, but looking at the question here you don't seem to present any indication to why you think he's wrong. Could you explain that, please? Saying that someone else is "full of it", and then not explaining why you come to that conclusion really doesn't make for a great question. Feels more like a rant. – Marcus Müller Mar 28 '24 at 18:23
  • 1
    And I'll be honest here: there's high potential for great answers at very different levels of physics understanding, and from very different perspectives, with the experienced folks you find here. But I'm personally strongly disincentivized from writing an answer to a question that gives no indication at which level the asker disagrees with a technical statement presented to them, but gives indication of being dismissive towards people he disagrees with. So, I think it'd be nice if you could replace the accusation with an explanation of why precisely you think the person is wrong. – Marcus Müller Mar 28 '24 at 18:27
  • I just thought I could replace the antenna with a thumb tag and call it non-resonant and it would accept the same amount of current because of the tuner. That just sounds wrong to me, how can that be... – K3ZD Mar 29 '24 at 18:07

2 Answers2

3

I don't know what is meant by "accept current", but a non-resonant antenna, as long as it is at least a half wavelength, will have at least one place on the antenna where current can reach its maxima. Take an end-fed 5/8 wave vertical antenna, this has a current maxima just above the middle, a 1/4 wavelength from the end of the antenna, just as a half wave antenna does, and then another current loop that doesn't reach a maxima, just above the feed-point. These two current loops combine to make the far-field have more gain at the horizon than a half-wave antenna, and I don't think you'll find anyone who would say that the total radiated power is any lower than a resonant antenna, it's simply that the energy field is shaped differently due to the number and magnitude of the current loops.

Also remember, that any antenna that isn't a perfect multiple of a 1/4 wavelength of the frequency it's being used on, is a non-resonant antenna.

The red lines below, indicate the position and magnitude of the current loops on the various antennas. The blue arrows indicate the direction of the current on the antenna. Notice that lengths beyond 1/2 wavelength, you have current flowing in different directions. This causes constructive interference in some parts of the far-field, and destructive interference in other parts of the far-field.

enter image description here enter image description here These far-field plots are over "real ground".

Louis Seaman
  • 865
  • 2
  • 9
  • I see, maybe that's what he meant. To me a 5/8 is still resonant because of the loading coil and I thought by non-resonant he meant mismatched. But going with what you said, once the antenna is shorter than 1/4 then the statement no longer applies and since the length of the antenna was not specified, the statement as a whole is false, would you agree? – K3ZD Mar 29 '24 at 18:10
  • 2
    No, because you can't get an antenna to function efficiently without it being at least a halfwave electrically. Even a 1/4 wave ground plane is a 1/2 wave antenna electrically. For antennas shorter than a 1/4 wave counterpoised antennas, you either need a tuner or a loading coil to make them electrically a 1/2 wave. And 5/8 is a non-resonant antenna, 75-400j if I remember correctly; the fact you have to add a coil is because it is naturally non-resonant and the wrong impedance for a 50 Ohm system. The coil makes it resonant. – Louis Seaman Mar 29 '24 at 18:22
  • When thinking about your question, I think your point is that you assume no impedance matching of the non-resonant antenna, and in that case you might be tempted to say non-resonant antenna don't radiate as well, but even that would not be correct, as whatever energy made it past the mismatch, would be radiated. The question assumes the antenna feedpoint impedance is matched, – Louis Seaman Mar 30 '24 at 08:52
  • and I can see where that's confusing. But this is like saying an end-fed 1/2 wave is a resonant antenna, so it should be able to be connected directly to 50 ohm coax and radiate efficiently, no, not without impedance matching first. So the question does assume impedance matching to your system impedance of a non-reaonant antenna length, but so would anybody who descibes any antenna and its efficiency. – Louis Seaman Mar 30 '24 at 08:52
-3

Ohm’s Law gives you the answer. Power = Current x Voltage. 0 amps x 100 trillion volts = 0 watts. You cannot have power without a current.

He is half right, but you do not need a tuner for all nonresonant antennas. For example, a random wire antenna does not require a tuner if cut to a specific nonresonant length of 73 or 136 feet. The 9:1 Balun brings the SWR down to acceptable levels below 2.

Dereck
  • 373
  • 1
  • 4
  • Ohm's law doesn't apply to antennas; so, this is not an argument for nor against the statement of the video. If one followed your argument, then no radio would be possible: because no current flows from the transmitter to my receiver, no power could be transported. – Marcus Müller Mar 28 '24 at 18:12