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#11
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where does the power when using an antenna-tuner go to ?
Hi Rob, Jim, Jef, all.
Thanks for continuing on this small thread. As said, I asked this as a fundamental" question, so I am really learning a lot here. (see inline comment) On 15/07/2020 16:27, Rob wrote: Antenna Matching Units ( I prefer not to use the word "Tuner") do have fixed resistance in inductors and wiring as has been stated in this thread. No! The amount of inductance varies depending on how much of the inductor is used, thus the resistance of the unit varies with the setting. OK. makes sense. Resistance also varies with frequency since the skin effect is "deeper" (lower resistance) with lower frequency. Correct me if I am wrong, but it looks to me that these two elements (partly) counter each other. To tune / match an antenna for a lower frequency, you need more inductor wire (i.e. greater resistor), but the skin-effect will be lower. BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. Are there figures of how much resistances the skin effect adds to a wire, in respect to the frequency? (Just to get an idea of the scale of things) And, the antenna resistance to be matched also varies. When the antenna is too short it will have a lower resistance This is something I do not completely understand. I guess you are talking the radiation resistance, correct? As far as I understand it, the radiation resistance is a "virtual" resistance which is created by the fact that an antenna converts electrical energy in electromagnetic waves that are radiated, thereby extracting energy from the wire. This "loss of energy" in the wire is modelled as a virtual resistance. So, saying "a short antenna has a lower resistance then a full-size antenna", is then the same as saying "a short antenna emits less energy then a full size antenna", which is equivalent to "a short antenna is less efficient" So isn't this a circular reasoning? What exactly is the reason that a short antenna has a lower resistance? .., and thus any fixed losses in tuner and feeder will have a higher relative effect. So, are there are then two different effects at play he - the resistance of the tuner/matching unit which changes with frequency due to the practical way it is build - the radiation resistance of the antenna that changes with frequency. All in all it is a completely wrong assumption that the losses will be independent from frequency, even when te resistive values in the tuner would be the same. 73 Kristoff - ON1ARF |
#12
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where does the power when using an antenna-tuner go to ?
kristoff wrote:
BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. So according to you the use of litze wire in medium wave (1 MHz) radios was a waste of effort? You seem to have a lot of strange ideas... |
#13
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where does the power when using an antenna-tuner go to ?
Rob,
On 20/07/2020 10:29, Rob wrote: BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. So according to you the use of litze wire in medium wave (1 MHz) radios was a waste of effort? You seem to have a lot of strange ideas... Well, what did you expect? I'm just a ham. You know: for 90 % no idea what I am doing as I am just an operator and for 9.9 % "no idea why it is like that, but that's what they told so it must be correct". I'm just trying to fill that 0.1 % of *really* understanding the technology I am using. Usually, I am more into DSP, SDR, data-communication, signal-processing, GNU Radio, etc. Signal processing is based on numeric representations of voltages (amplitude and phase), either the time or frequency-domain, at one particular place in the circuit. The most interesting part of this discussion here is that it requires me to think in a different way that I am used to do, so this discussion is very interesting to me. The problem is that, saying "the skin-effect also has an effect" but without really quantising it does not really help. I still do not have an answer to my question: Are there figures of how much resistances the skin effect adds to a wire, in respect to the frequency? (Just to get an idea of the scale of things) Say for a very basic HF antenna-system: 10 meter coax, balun, full-length dipole for -say- the 40 meter band, designed for 100 Watt RF power. Can you put some numbers of the impact of the skin-effect on this kind of system? 73 kristoff - ON1ARF |
#14
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where does the power when using an antenna-tuner go to ?
kristoff wrote:
Rob, On 20/07/2020 10:29, Rob wrote: BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. So according to you the use of litze wire in medium wave (1 MHz) radios was a waste of effort? You seem to have a lot of strange ideas... Well, what did you expect? I'm just a ham. You know: for 90 % no idea what I am doing as I am just an operator and for 9.9 % "no idea why it is like that, but that's what they told so it must be correct". Well actually this is a bit strange, because a ham usually has to pass an exam, and the theory that has to be learned from that usually includes the basic principles of HF electronics, including a discussion of things like L/C circuits, Q factor, skin effect, etc. But maybe you only did a crash course and pre-learned the 500 questions and their correct answer, without actually understanding it. Well, hopefully you will learn from the current discussion. |
#15
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where does the power when using an antenna-tuner go to ?
On 7/21/2020 1:31 PM, kristoff wrote:
Rob, On 20/07/2020 10:29, Rob wrote: BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. So according to you the use of litze wire in medium wave (1 MHz) radios was a waste of effort? You seem to have a lot of strange ideas... Well, what did you expect? I'm just a ham. You know: for 90 % no idea what I am doing as I am just an operator and for 9.9 % "no idea why it is like that, but that's what they told so it must be correct". I'm just trying to fill that 0.1 % of *really* understanding the technology I am using. Usually, I am more into DSP, SDR, data-communication, signal-processing, GNU Radio, etc. Signal processing is based on numeric representations of voltages (amplitude and phase), either the time or frequency-domain, at one particular place in the circuit. The most interesting part of this discussion here is that it requires me to think in a different way that I am used to do, so this discussion is very interesting to me. The problem is that, saying "the skin-effect also has an effect" but without really quantising it does not really help. I still do not have an answer to my question: Are there figures of how much resistances the skin effect adds to a wire, in respect to the frequency? (Just to get an idea of the scale of things) Say for a very basic HF antenna-system: 10 meter coax, balun, full-length dipole for -say- the 40 meter band, designed for 100 Watt RF power. Can you put some numbers of the impact of the skin-effect on this kind of system? 73 kristoff - ON1ARF Here ya go... you can put in the numbers yourself. https://chemandy.com/calculators/ski...calculator.htm |
#16
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where does the power when using an antenna-tuner go to ?
On 7/21/2020 1:31 PM, kristoff wrote:
Rob, On 20/07/2020 10:29, Rob wrote: BTW. I always had the idea that skin-effect was only important for frequencies of VHF and higher, not for HF. So according to you the use of litze wire in medium wave (1 MHz) radios was a waste of effort? You seem to have a lot of strange ideas... Well, what did you expect? I'm just a ham. You know: for 90 % no idea what I am doing as I am just an operator and for 9.9 % "no idea why it is like that, but that's what they told so it must be correct". I'm just trying to fill that 0.1 % of *really* understanding the technology I am using. Usually, I am more into DSP, SDR, data-communication, signal-processing, GNU Radio, etc. Signal processing is based on numeric representations of voltages (amplitude and phase), either the time or frequency-domain, at one particular place in the circuit. The most interesting part of this discussion here is that it requires me to think in a different way that I am used to do, so this discussion is very interesting to me. The problem is that, saying "the skin-effect also has an effect" but without really quantising it does not really help. I still do not have an answer to my question: Are there figures of how much resistances the skin effect adds to a wire, in respect to the frequency? (Just to get an idea of the scale of things) Say for a very basic HF antenna-system: 10 meter coax, balun, full-length dipole for -say- the 40 meter band, designed for 100 Watt RF power. Can you put some numbers of the impact of the skin-effect on this kind of system? 73 kristoff - ON1ARF There is abundant information of the Web about skin effect. Have you even tried searching? Or are you just trolling? |
#17
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where does the power when using an antenna-tuner go to ?
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#19
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where does the power when using an antenna-tuner go to ?
Ralph, all,
On 21/07/2020 22:52, Ralph Mowery wrote: Well actually this is a bit strange, because a ham usually has to pass an exam, and the theory that has to be learned from that usually includes the basic principles of HF electronics, including a discussion of things like L/C circuits, Q factor, skin effect, etc. But maybe you only did a crash course and pre-learned the 500 questions and their correct answer, without actually understanding it. The test of the last 20 or 30 years have been a joke. Anyone with a memory can pass those without knowing anything. Well, I have this discussion a number of times. (I man a infobooth to promote amateur-radio at FOSDEM -a yearly conference on open-source development in Brussels- so I get to explain this quite a lot) In essence, that is not the problem with the exam itself. When explaining to people why you need to do an exam for amateur-radio, I compare this to a drivers-license. A drivers-license is to show that you are technically capable to drive a car on the public road in a way that is safe for yourself and others on the road. This is very similar to the the amateur-radio exam: it is to make sure that you have sufficient technical knowledge to transmit without interfering with other radio-users and to make sure you do not blow up yourself. The only additional element here is that we are not only allowed to drive a car, but to also build one ourself; so, you have to show you are technically able to build a basic model of a transmitter. So, in essence, the exam still serves it goal: allow all users of the radio-spectrum operate without to much "bumping into each-other". But there is very different problem: The problem is that radio-technology nowadays is nowhere near the technology when the exams where conceived. I did my exam in 1992 (when I was in the 2nd year of what would now be a professional bachelor (digital) electronics). I do not think that the exam has really changed in that 28 years. The "problem" is that technology DID really change. Electronics is now a lot more digital and software, and -especially- the way you do electronics has changed dramatically. I think the exam in Belgium now has just two questions one SDR, one asking of a drawing is a FIR filter and one asking if it is a IIR filter. (and yes, most people just learn it by heart: "is there is line going back from the last block of the drawing to the beginning, , it's answer 2. If not, it is answer 1). In essence, the problem is that the amateur-radio exam requires you to know how to build a car ... a basic model of a car: chassis, 4 wheels, engine, breaks, suspension, fuel, .... However, the reality is that a car build in 2020 is 100 times more complex than that basic model. A modern car is filled with hundreds of sensors and as many microcontrollers that all talk together over any number of CAM-bus. After all, the goal is that -if the driver hits the break and the sensors in the wheels notice that the car is losing grip- some device will take over and -based on the input of a myriad of other sensors determining the state of the car- and try to keep the car going in a direction the driver wants it to go. In amateur-radio terms, almost any device you buy or build these-days is driven by DSP, SDR, microcontrollers, FPGAs, etc. We use plutoSDRs to transmit to QO100, arduino's to drive a PLL as a cheap WSPR beacon in a 3d-printed case and a raspberry-pi as signal-generator for DATV. And the exam does not reflect that. Should it do that? Should there be a question on the amateur-radio exam: "please provide a general overview of the hardware and software for a POCSAG paging transmitter using either an arduino + FM transmitter or a si4332 radio-chip"? I don't think so. .. that is simply not the goal of the exam. But, the problem is that, if you do not require this knowledge for the exam, 99 % of the amateur-radio community is completely clueless on how modern telecommunication-equipment works internally. So either they do not care "I'm just an operator and I know how to use my radio", or they have a very vague idea of how it works. As explained, my interest here is to learn. Antenna's are not my speciality (as you can guess). I learned about them in school (which was good enough to pass the ham-radio exam) but that does not mean I "understand" it. In fact, it was a presentation of my former teacher in our radio-club on the nanovna, the video of a talk by Dr. KC Kerby-Patel at MIT about antenna's beginning this year and a discussion I had at FOSDEM with a somebody working in the physics department of a university that made me for the first time see an antenna in the context of "energy". I have been playing around with the Java tool Jeff pointed out (I'm also trying to really understand the article he has provided) and been playing around with a couple of xnec2 simulations. I kind-of favour the idea that this loss is pure related to the practice components (as Jeff and Jeff have said), but I do not understand how this matches up with a statement that the resistance of a shortened antenna is less then a that of a full-size antenna. Concerning the skin-effect, I did read some information on it, and just tried the tool that John has provided (I already had that formula so it saves me time having to do the calculations :-) ), but the problem is that the result does not really say that much. What does a skin-effect depth of 24.46 μm (copper, 7.1 MHz) say concerning additional resistance to an antenna-system and how to does this compare to other resistive elements in the antenna-system and the overall behaviour? As said, there is a difference between "having learned" and "understanding". 73 kristoff - ON1ARF |
#20
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where does the power when using an antenna-tuner go to ?
In article , kristoff
wrote: What does a skin-effect depth of 24.46 μm (copper, 7.1 MHz) say concerning additional resistance to an antenna-system and how to does this compare to other resistive elements in the antenna-system and the overall behaviour? As said, there is a difference between "having learned" and "understanding". Kristoff- I can not discuss the physics of skin effect. I learned of its existence in passing, with the understanding that it is relatively insignificant. For radio systems, I think in terms of Decibels. For voice, in every step between your mouth and the ear of the receiving station, there is a series of stages of positive and negative amplification. You may have 100 Watts peak power coming out of the transmitter. The receiving station might have one Watt peak audio coming out of their speaker. By far, the greatest negative amplification (loss) is between antennas. Fred |
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