Actually the VHF/UHF/Microwave guys do some limited relative measurements in a amateur antenna field with relative vs. absolute type readings. You're correct, calibrated field strength meters are very expensive. Having said that you can, even with the little Monarch brand combo SWR/FS meter I used as a Novice in 1969 make some albeit crude measurements that can be useful (still have it!). A simple example is attaching a "stinger" to a HT (extra ground wire just under the connector) and see a significant increase in FS at the same distance as without it. Yep, not quantitative but at least a very crude qualitative indicationt. Thanks for the explanation, I've shared this video with my fellow instructors in our General Class upgrade group to give them some additional ideas about how to better explain the concept in class. Love the Antenna Handbook, that was my first one as well! ;-)
And to think I could have purchased an Anechoic chamber for $1,000 when my company down sized and moved but it would have cost me $5,000 to move it and another $25,000 to set it up I didn't win the lotto that week and am still crying. Sure would have been nice to have an Anechoic chamber sitting in my backyard LOL Great analogy using light! By using the VNA you can measure the S11 than calculate the loss which than you can figure out it's efficiency. 73 N8AUM
what is described here is antenna Directivity which is independent of impedance matching (VSWR) and losses. Antenna "Gain" on the other hand does depend on losses and also impedance matching although the pattern looks the same as Directivity (take the directivity and just factor out the losses and mismatch then it becomes Gain) I have yet to see an anechoic chamber where the receiver antenna moves around a sphere in the far field of a fixed test antenna! The receiver is always fixed (in some chambers it has its own turn table too but in fixed position) and the test antenna is also fixed on a turn table and that table rotates in its place and all azimuth and elevation angles between the receiver and test antenna are covered this way. Nothing moves around the chamber on a spherical surface as indicated in the video
Thanks for sharing. Can you explain how the ground plane acts like a reflector? It seems like the transmitted power that hits the ground plane would be absorbed not reflected.
welcome to electro magnetism. Radio waves and photons are the same thing just different sizes. Mirrors work right? the light is not absorbed but reflected. from a search: "Mirrors reflect mainly because they are electrically conductive. Light is an electromagnetic field, and when it hits a mirror the metal inside of it (usually aluminum or silver) cancels out the electric field parallel to the mirror which causes it to change directions and reflect away." . Consult Mr. Maxwell for more....
The ground DOES reflect radio waves and depending on the type of soil (ground) will have a great effect. Simple example: I live in Florida which is mostly SAND so my Dipole that is 20ft. high works like a Dipole that's at 30ft if I lived up north with Clay underneath. People use to pour salt on the ground to make the ground conduct better.
Actually the VHF/UHF/Microwave guys do some limited relative measurements in a amateur antenna field with relative vs. absolute type readings. You're correct, calibrated field strength meters are very expensive. Having said that you can, even with the little Monarch brand combo SWR/FS meter I used as a Novice in 1969 make some albeit crude measurements that can be useful (still have it!). A simple example is attaching a "stinger" to a HT (extra ground wire just under the connector) and see a significant increase in FS at the same distance as without it. Yep, not quantitative but at least a very crude qualitative indicationt. Thanks for the explanation, I've shared this video with my fellow instructors in our General Class upgrade group to give them some additional ideas about how to better explain the concept in class. Love the Antenna Handbook, that was my first one as well! ;-)
Great Sir 👌.. You just answer my questions. Very appreciated you explanations about antenna gain measurements.Thank you.
And to think I could have purchased an Anechoic chamber for $1,000 when my company down sized and moved but it would have cost me $5,000 to move it and another $25,000 to set it up I didn't win the lotto that week and am still crying. Sure would have been nice to have an Anechoic chamber sitting in my backyard LOL Great analogy using light! By using the VNA you can measure the S11 than calculate the loss which than you can figure out it's efficiency. 73 N8AUM
what is described here is antenna Directivity which is independent of impedance matching (VSWR) and losses. Antenna "Gain" on the other hand does depend on losses and also impedance matching although the pattern looks the same as Directivity (take the directivity and just factor out the losses and mismatch then it becomes Gain)
I have yet to see an anechoic chamber where the receiver antenna moves around a sphere in the far field of a fixed test antenna! The receiver is always fixed (in some chambers it has its own turn table too but in fixed position) and the test antenna is also fixed on a turn table and that table rotates in its place and all azimuth and elevation angles between the receiver and test antenna are covered this way. Nothing moves around the chamber on a spherical surface as indicated in the video
Did u covered onmmi all directional antenna like a commet with ground
Thanks for sharing. Can you explain how the ground plane acts like a reflector? It seems like the transmitted power that hits the ground plane would be absorbed not reflected.
welcome to electro magnetism. Radio waves and photons are the same thing just different sizes. Mirrors work right? the light is not absorbed but reflected. from a search: "Mirrors reflect mainly because they are electrically conductive. Light is an electromagnetic field, and when it hits a mirror the metal inside of it (usually aluminum or silver) cancels out the electric field parallel to the mirror which causes it to change directions and reflect away." . Consult Mr. Maxwell for more....
The ground DOES reflect radio waves and depending on the type of soil (ground) will have a great effect. Simple example: I live in Florida which is mostly SAND so my Dipole that is 20ft. high works like a Dipole that's at 30ft if I lived up north with Clay underneath. People use to pour salt on the ground to make the ground conduct better.