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There is a surprising lack of easily digestable antenna/ham radio related material on the internet. I know because it took me 3 weeks to learn the basics of ant

There is a surprising lack of easily digestable antenna/ham radio related material on the internet. I know because it took me 3 weeks to learn the basics of antennas when I expected to finish in 2 nights. Some of the best information I read was from old Royal Canadian Airforce videos, atleast several decades old[0] I still haven't been able to find a general equation for a have wavelength dipole antenna explained in simple English. I do have one based on empirical evidence, though[1]. I've even bought a copy of the ARRL Handbook, but I find that it goes from 0 to OMG-language-is-this too quickly. Thank you, I wish I'd found this site earlier. [0]: https://www.youtube.com/watch?v=7bDyA5t1ldU https://www.youtube.com/watch?v=7bDyA5t1ldU [1]: https://ham.stackexchange.com/questions/12996/what-is-the-equation-for-the-arm-lengths-of-a-half-wavelength-dipole-antenna https://ham.stackexchange.com/questions/12996/what-is-the-eq...

dbcurtis 8y ago
>I still haven't been able to find a general equation for a have wavelength dipole antenna explained in simple English. Equation for what? Length at resonance? Feed point impedance? Other interesting parameters? Antennas are one of those things where it takes a long time to develop intuition, and there are no simple formulas for anything, just useful models that get you close, and simulation programs that work well enough to give an answer within your manufacturing tolerances. (All models are wrong, some are useful.) So start with a couple of fundamental ideas: 1) Accelerate an electron, get a photon. 2) An antenna is a transformer that couples the end of your feed line to free space. The reason the general family of dipole antennas is efficient is that the Ohmic resistance is usually around an Ohm or less, and the "radiation resistance" can be raised to around 70 to 80 Ohms. So 80/(80+1) is the ratio of energy coupled to space versus total energy input. Pretty good efficiency. In a center fed dipole, the driving voltage creates an electrostatic force that attempts to slosh electrons in the conductor one way or the other. At resonance, a small amount of energy input creates lots of sloshing, because the driving voltage just needs to give a boost to the resonant sloshing. Off resonance, effectiveness is much lower. Actual length at resonance depends on the length:diameter ratio of the conductor, the dielectric constant of the surrounding medium, the height above ground, and the dielectric constant and conductivity of the ground. If you know all of those, the dipole can be modeled as a just barely tractable boundary value problem. The empirical formulas that you see usually assume a practical conductor diameter and practical height. You might enjoy playing with one of the NEC2-based antenna modeling programs out there. NEC2-family solvers do "method of moments", where each wire is chopped up into segments, and then for an N-segment model, an NxN matrix of mutual inductances models the coupling among wire segments. The ARRL Antenna Book takes more time to explain fundamentals than the Handbook. The ARRL also publishes an antenna physics book that I haven't read. I notice that PhD committee chair for the author of the Antenna Theory web site we are yakking about was Balanis, who wrote a pretty good book called "Antenna Theory" -- but the book assumes you are an EE graduate student with at least a semester of multi-dimmensional DiffEQ beyond the elementary DiffEQ course.
- amingilani 8y ago
  That's the problem I suppose. Most of the material is either geared for EEs, or assumes I need a refresher. Not someone completely new to the hobby. >Equation for what? Length at resonance? Feed point impedance? Other interesting parameters? I should have clarified: The arm length of a half wavelength dipole and all the variables that go into it. I assumed it was 1/4 wavelength, but while building mine, I discovered calculators that gave calculations different from mine. >So start with a couple of fundamental ideas: 1) Accelerate an electron, get a photon. 2) An antenna is a transformer that couples the end of your feed line to free space. I don't mean to sound thick, but you've already assumed too much. Before I signed up for a membership with my local radio society, I didn't even know Ohm's law. I pride myself in being technical. If I can teach myself to code and, in a few years, craft tested API's and decoupled front-ends that are tested through CI pipelines and deploy through CD, I can surely teach myself enough physics to build an antenna — no. I still struggle to understand basic concepts like: + Baluns + Why does the height of an antenna effect its effectiveness? + Gain + Circuit design + Transistors + Honestly, I still think radio waves are magic sometimes, even though I think I've seen the effects of electrically generated magnetic fields on coils >You might enjoy playing with one of the NEC2-based antenna modeling programs out there. Tried playing with CocoaNEC 2.0, but the lack of documentation left me feeling like an air head. I'm hoping a little more exposure to electrical systems will help.
  - rfdave 8y ago
    You're trying for a huge breadth of material, stuff that is covered in multiple specialities in electrical engineering. Multivariable calculus is really the entry point for engineering level antenna design. Balanis is the book I used in my antennas class, https://www.amazon.com/Antenna-Theory-Analysis-Constantine-Balanis-ebook/dp/B01A0393XG/ref=sr_1_1?crid=H3F47WRBE8RA&keywords=balanis+antenna+theory&qid=1555810869&s=gateway&sprefix=balanis%2Caps%2C207&sr=8-1 https://www.amazon.com/Antenna-Theory-Analysis-Constantine-B... but you'll need multivariable calculus to get through it.
    - Junk_Collector 8y ago
      Balanis' book is a great reference but I wouldn't recommend it for learning. Honestly the ARRL antenna book and antenna handbook are the best practical books on putting an antenna together without getting bogged down in the details. The real hard part is getting some radio equipment so that you can experiment and learn since Spectrum and Network analyzers are waaaay out of most people's hobby budgets.
ac29 8y ago
I really liked the free Anritsu e-learning course "RF Fundamentals", which I did earlier this year: https://us.anritsu-learning.com/course/categorylist.php?viewtype=course https://us.anritsu-learning.com/course/categorylist.php?view... I work in the radio industry, and it was very useful when putting together training materials. You need a free account to access it.
- amingilani 8y ago
  This might just be the most helpful thing someone has pointed me to! Thank you! Here's the syllabus for anyone else looking to check it out: Radio Frequency: Module 1 Decibels: Module 2 Modulation: Module 3 RF Impairment: Module 4 Antennas: Module 5 Coaxial Cables: Module 6 Components: Module 7 Propagation: Module 8 Microwave: Module 9

dbcurtis 8y ago

>I still haven't been able to find a general equation for a have wavelength dipole antenna explained in simple English. Equation for what? Length at resonance? Feed point impedance? Other interesting parameters? Antennas are one of those things where it takes a long time to develop intuition, and there are no simple formulas for anything, just useful models that get you close, and simulation programs that work well enough to give an answer within your manufacturing tolerances. (All models are wrong, some are useful.) So start with a couple of fundamental ideas: 1) Accelerate an electron, get a photon. 2) An antenna is a transformer that couples the end of your feed line to free space. The reason the general family of dipole antennas is efficient is that the Ohmic resistance is usually around an Ohm or less, and the "radiation resistance" can be raised to around 70 to 80 Ohms. So 80/(80+1) is the ratio of energy coupled to space versus total energy input. Pretty good efficiency. In a center fed dipole, the driving voltage creates an electrostatic force that attempts to slosh electrons in the conductor one way or the other. At resonance, a small amount of energy input creates lots of sloshing, because the driving voltage just needs to give a boost to the resonant sloshing. Off resonance, effectiveness is much lower. Actual length at resonance depends on the length:diameter ratio of the conductor, the dielectric constant of the surrounding medium, the height above ground, and the dielectric constant and conductivity of the ground. If you know all of those, the dipole can be modeled as a just barely tractable boundary value problem. The empirical formulas that you see usually assume a practical conductor diameter and practical height. You might enjoy playing with one of the NEC2-based antenna modeling programs out there. NEC2-family solvers do "method of moments", where each wire is chopped up into segments, and then for an N-segment model, an NxN matrix of mutual inductances models the coupling among wire segments. The ARRL Antenna Book takes more time to explain fundamentals than the Handbook. The ARRL also publishes an antenna physics book that I haven't read. I notice that PhD committee chair for the author of the Antenna Theory web site we are yakking about was Balanis, who wrote a pretty good book called "Antenna Theory" -- but the book assumes you are an EE graduate student with at least a semester of multi-dimmensional DiffEQ beyond the elementary DiffEQ course.

amingilani 8y ago
That's the problem I suppose. Most of the material is either geared for EEs, or assumes I need a refresher. Not someone completely new to the hobby. >Equation for what? Length at resonance? Feed point impedance? Other interesting parameters? I should have clarified: The arm length of a half wavelength dipole and all the variables that go into it. I assumed it was 1/4 wavelength, but while building mine, I discovered calculators that gave calculations different from mine. >So start with a couple of fundamental ideas: 1) Accelerate an electron, get a photon. 2) An antenna is a transformer that couples the end of your feed line to free space. I don't mean to sound thick, but you've already assumed too much. Before I signed up for a membership with my local radio society, I didn't even know Ohm's law. I pride myself in being technical. If I can teach myself to code and, in a few years, craft tested API's and decoupled front-ends that are tested through CI pipelines and deploy through CD, I can surely teach myself enough physics to build an antenna — no. I still struggle to understand basic concepts like: + Baluns + Why does the height of an antenna effect its effectiveness? + Gain + Circuit design + Transistors + Honestly, I still think radio waves are magic sometimes, even though I think I've seen the effects of electrically generated magnetic fields on coils >You might enjoy playing with one of the NEC2-based antenna modeling programs out there. Tried playing with CocoaNEC 2.0, but the lack of documentation left me feeling like an air head. I'm hoping a little more exposure to electrical systems will help.
- rfdave 8y ago
  You're trying for a huge breadth of material, stuff that is covered in multiple specialities in electrical engineering. Multivariable calculus is really the entry point for engineering level antenna design. Balanis is the book I used in my antennas class, https://www.amazon.com/Antenna-Theory-Analysis-Constantine-Balanis-ebook/dp/B01A0393XG/ref=sr_1_1?crid=H3F47WRBE8RA&keywords=balanis+antenna+theory&qid=1555810869&s=gateway&sprefix=balanis%2Caps%2C207&sr=8-1 https://www.amazon.com/Antenna-Theory-Analysis-Constantine-B... but you'll need multivariable calculus to get through it.
  - Junk_Collector 8y ago
    Balanis' book is a great reference but I wouldn't recommend it for learning. Honestly the ARRL antenna book and antenna handbook are the best practical books on putting an antenna together without getting bogged down in the details. The real hard part is getting some radio equipment so that you can experiment and learn since Spectrum and Network analyzers are waaaay out of most people's hobby budgets.

ac29 8y ago

I really liked the free Anritsu e-learning course "RF Fundamentals", which I did earlier this year: https://us.anritsu-learning.com/course/categorylist.php?viewtype=course https://us.anritsu-learning.com/course/categorylist.php?view... I work in the radio industry, and it was very useful when putting together training materials. You need a free account to access it.

amingilani 8y ago
This might just be the most helpful thing someone has pointed me to! Thank you! Here's the syllabus for anyone else looking to check it out: Radio Frequency: Module 1 Decibels: Module 2 Modulation: Module 3 RF Impairment: Module 4 Antennas: Module 5 Coaxial Cables: Module 6 Components: Module 7 Propagation: Module 8 Microwave: Module 9