Here’s your video introduction to Section 10.3, “VHF/UHF/Microwave Propagation,” from the 11th Edition of the ARRL Extra Class License Manual for Ham Radio.
You can find a complete list of the Amateur Extra videos by clicking here, or click here to go to the YouTube Amateur Extra playlist. Please post your questions either below or on the YouTube page for this video. Good luck in your studies!
Hello Dave and Bob!
Dave, this is my first time listening and watching your video’s. I’ve been licensed since 1975, life member with ARRL, and presently a Tech Specialist with ARRL. I noticed you mention using Horizontal polarization as “Just the convention chosen”. Actually, the reason horizontal polarization is chosen is due to man made noise. All of man made noise is vertically polarized. So when choosing horizontal polarization you are also cancelling out the man made noise. Bob, you ask about the polarization in HF. In HF you can use both with success however, in choosing vertical polarizations (such as verticals antenna’s) your noise floor will be much higher due to man made noise. I hope this makes sense?
Jim (K7QI/ Z81A)
I’m enjoying your Ask Dave and License Study videos. I recently got your Flash Drive with the Extra Class videos for a General Class friend who is determined to get his Extra. (His wife got hers already!)
In your discussion about Weak Signal vs FM antenna polarization, I can agree that the choices are mostly arbitrary and just done by common practice.
However, I wonder if there is some historical background? Dipoles and similar wire antennas are pretty much always horizontal, so use of horizontal for weak signal is possibly a natural outgrowth of that. Further, at shorter wavelengths, the ground reflection may be better for horizontal polarization.
For the most part, horizontally polarized mobile installations are not practical, although more so at VHF and UHF it might me easier to work out. Halo/Squalo hoops, for example.
I wonder if that’s why we see mostly vertical polarization on FM, since the practices are in a great part derived from land mobile services.
Just a thought. The distinction is not really significant for the purpose of the exam study.
Morgantown West Virginia