Cable Antennas - 1/2 and 1/4 Wavelength Antenna

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Cable Antennas - 1/2 and 1/4 Wavelength Antenna

Рет қаралды 2,095

8 ай бұрын

We frequently receive inquiries from engineers, particularly those in the mechanical and systems engineering fields, regarding cable connections between systems. They wonder why, in certain instances, noise levels differ significantly at various frequencies, and even minor adjustments yield markedly different outcomes. The realm of antennas can be complex to grasp, so we've created this video in the hopes of shedding some light on the subject.

Пікірлер: 15

@hungdo4611 7 ай бұрын

Thank you for everything you've done for the EMC community.

@MachOneDesignEMC 4 ай бұрын

thanks, not enough as I hope, but i will try.

@cristiannegru9534 3 ай бұрын

Hello Min, First I want to thank you for sharing your knowledge and experience with the community. This is very valuable because it is valid. I see mach bullshit on the WEB. I can say you contribute positively to the public knowledge and I congratulate you for this. I like your direct style. You two important things. 1st your are young (willing to discover and to be enthusiastic); 2nd you have the knowledge to speak about EMC. So keep up the good work. The future will tell if these videos will stay or leave within the community. In regard to the subject of this video, it is very nice explained one of the most common EMI issue found in practice. Ie in automotive (where I'm activating as EMC eng.) we use 2m length harness between the EUT and various loads. The wires in the harness has different resonances and they always get in to trouble the project. If this is not treated correctly, it can make a difference between pass and fail. So I think it would be a good idea if you can continue this series about cable resonance with another movie demonstrate how can a such problem could be solved (cancel the resonance) in practice. Again, many thanks for what you are doing on this field.

@MachOneDesignEMC 3 ай бұрын

many thanks Cristian for your kind feedback, we will try to keep up the work, I will also take your suggestions into consideration and make one video on that soon!

@ininjad24 2 ай бұрын

Again a very good video that demonstrates resonant frequency as function of cable length/impedance 👍 How does it work when single core cables carry pulse width modulated current at switching frequencies in the range of 1 to 20 kHz with rise/fall times in nano seconds, for e.g., in UPS or VFD?

@user-jl2ug8ns9b 3 ай бұрын

Hello Dr Min, Just making sure, when connecting ( HH, LL , HL, LH ) C.M impedances to the ends of out Coaxe cable, by saying it becomes λ/4 & λ/2 antennas , you mean that it physically becomes Monopole or dipole ? Thanks you.

@sleeve8651 17 күн бұрын

Electrical length is always some what longer, than physical length, as even shown by you your calculations, and that of the scope, correct ? 🤔......? This being true, wouldn't you have to take this into consideration, when cutting a, " Coaxial " cable to a specific length ? Where because of its electrical length being somewhat longer, the physical length of the Coax, would be shorter in order to keep it's impedance ?

@MachOneDesignEMC 3 күн бұрын

Yes, you got it. But we don't tend to match the physical length with electrical length. After all, it is only electrical length matter in a sense as waves propagate at a certain speed (in this case, less than the speed of light) in a given geometry of the transmission line.

@harrysun5155 4 ай бұрын

Thanks for sharing. one question, how did you get that 0.7 factor?

@MachOneDesignEMC 4 ай бұрын

Hi Harry, as we assume the EM wave travels in the free space at the seped of light. When EM wave travels on a cable structure, due to the dialetrics of the insulation material, the velocity of propagation is slower than the speed of light, generally, I apply 0.7-0.8 as a rule of thumb kind of thing. Hope this makes sense?

@harrysun5155 4 ай бұрын

@@MachOneDesignEMC thanks a lot. make sense to me, it may have answered long time due question in my head why my calculation in theory has never matched the reality. by the way, i am an experienced EMC engineer and i think you are the only one i have encountered that truly knows the black magic. your potential is tremendous, keep going. last question is that i am interested in your emc class online, but as i am experienced, i am thinking the stuff on your website might be too generic for me, what do you recommend?

@PSPS437 7 ай бұрын

May be a dumb question, please advise. A laptop adapter has a cable. At what wavelength does it radiate? quarter or half wavelength?

@davidbonds3571 7 ай бұрын

No worries, not a dumb question. The answer is that the cable will radiate all frequencies. It will be the most efficient radiator at certain resonant frequencies. At other frequencies it will be less effective, but it will still radiate to a lesser degree.

@PSPS437 7 ай бұрын

@@davidbonds3571 Hi David, sorry doesn't answer my question. My question is straightforward. How can one say that 40cm is quarter wavelength vs 80cm is half wavelength. If this is the case, what is the wavelength at which 1.8m or 2m adapter cable dominantly radiates? Or should the radiation be measured, then back calculated to quarter or half wavelength?

@MachOneDesignEMC 4 ай бұрын

Hi, that is a very good question, it depends on the terminations, so for example, if a cable is terminated in a metal enclosure, then often we treat this end as low impedance, if the other end is somehow high impedance (it could be the case that on the end, the cable is termianted with a plastic enclosure), then it is a quarterwave length antenna most likely. Notice, here when i said impedance, I meant the common mode impedance, i.e. depending on parastic capcitance/inductance. @@PSPS437