Timeline for How to probe a dipole antenna?
Current License: CC BY-SA 3.0
20 events
| when toggle format | what | by | license | comment | |
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| Jun 25, 2017 at 0:37 | comment | added | Mike Waters | @Xynon We admire your attitude! Please stick around. :-) Check out these pages: ham.stackexchange.com/tour and ham.stackexchange.com/help and the subtopics there. Even though I'm a moderator, I'm still learning what's acceptable on this site. | |
| Jun 25, 2017 at 0:00 | comment | added | Xynon | Excuse me, I agree with both of you. I just hesitated about if this was important enough for a separate question. Thanks for your kindness. | |
| Jun 24, 2017 at 21:38 | comment | added | Kevin Reid AG6YO♦ | @Xynon It looks like you have a new question. Please post it separately — comments are not an appropriate place for doing that (in this case, I don't understand what you're asking!) | |
| Jun 24, 2017 at 21:34 | comment | added | Mike Waters | @Xynon Respectfully, you would do well to study the basics of these things. Google is your friend (and so is hamSE). Decades ago, I got to the point where I realized that I was not going to progress in my understanding (and enjoyment!) of the practical applications of radio and electronics that I was doing until I stopped and studied the basics. That learning was time very-well-spent, and it was fun, too! That's why I said that. :-) | |
| Jun 24, 2017 at 21:04 | comment | added | Xynon | Excuse me for this is off-topic but could we simply say that: 1- Coax core and braid has different impedances, 2-Therefore different rms currents under same rms voltages 3- Baluns can't change the impedances but they change the core and braid rms voltages so that they have equal rms currents with different impedances? | |
| Jun 24, 2017 at 20:45 | comment | added | Xynon | Thank you again for such clear and informative answers. How about a twin-lead enclosed in a shield (balanced coax)? An example here (local695.com/Quarterly/wp-content/uploads/…). I do not yet have a good enough understanding of what a transformer balun is doing (off-topic for this discussion) so I'm trying to avoid that. | |
| Jun 22, 2017 at 20:45 | comment | added | Kevin Reid AG6YO♦ | @GlennW9IQ I was referring to the cables running to the oscilloscope — between the intended point of measurement and the measurement instrument. | |
| Jun 22, 2017 at 20:44 | history | edited | Kevin Reid AG6YO♦ | CC BY-SA 3.0 |
added 101 characters in body
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| Jun 22, 2017 at 19:55 | comment | added | Glenn W9IQ | The comment "Also, since you want to compare phase, don't forget to consider the length of your cables. Use cables of the same length and type and you know they have the same delay." seems strange. If you mean the same length on the transmit and receive side this doesn't work. A 5° phase delay in the transmit cable is not negated by a 5° phase delay in the receive cable. But perhaps I am not catching your intent. | |
| Jun 21, 2017 at 15:22 | comment | added | Kevin Reid AG6YO♦ | @Xynon I've updated my answer to go into more detail on terminators & ground leads. | |
| Jun 21, 2017 at 15:21 | history | edited | Kevin Reid AG6YO♦ | CC BY-SA 3.0 |
clarify on terminators & ground lead
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| Jun 21, 2017 at 15:14 | history | edited | Kevin Reid AG6YO♦ | CC BY-SA 3.0 |
clarify on terminators & ground lead
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| Jun 21, 2017 at 7:07 | comment | added | Xynon | “...consider using a shorter ground lead to minimize the loop area (custom bent pieces of solid wire).” Do you mean I could use any piece of wire reasonably thick and bend/wrap one end of it around the probe’s ground connection part? | |
| Jun 21, 2017 at 7:01 | comment | added | Xynon | “You must include a 50 Ω load (terminator), either using a BNC tee or a feed-through terminator (typically more expensive), at the oscilloscope's end of the cable.” The feed-through terminators already have 50 ohms as I see. So we don’t use a 50 ohms terminator with these I suppose? But with the BNC tee, do we put a 50 ohms dummy load in parallel with the oscilloscope-coax line? | |
| Jun 21, 2017 at 6:58 | comment | added | Xynon | Thank you for the explanations and suggestions. Great answer. I suppose the probe and ground cables can act like two "arms of a dipole antenna" or like a high pass filter in the presence of radio waves. And when we short them via an antenna, we are basically forming a loop much like of a "current probe" by which we will be measuring induced voltages superimposed on the "point voltage" we are trying to see. So things can get misleading if we have a large loop area / magnetic dipole moment. | |
| Jun 21, 2017 at 6:50 | vote | accept | Xynon | ||
| Jun 19, 2017 at 21:37 | comment | added | Kevin Reid AG6YO♦ | @MikeWaters Thank you, I have added a mention of that. | |
| Jun 19, 2017 at 21:36 | history | edited | Kevin Reid AG6YO♦ | CC BY-SA 3.0 |
added 464 characters in body
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| Jun 19, 2017 at 21:22 | comment | added | Mike Waters | Since you seem to be interested in precision measurements, be aware that the feedpoint Z of a dipole is seldom 50 ohms. Look at this graph of feedpoint Z vs height | |
| Jun 19, 2017 at 20:54 | history | answered | Kevin Reid AG6YO♦ | CC BY-SA 3.0 |
