Wednesday, May 8, 2013

Lesson 8- VHF, UHF, HF, What's the difference?

Radio waves are grouped in general by powers of 10. There are 4 key radio bands, UHF, VHF, HF, and MF, within Amateur Radio that have very different characteristics, which I will explain in this post, along with some of their strengths and weaknesses. While there are bands even higher frequency than UHF, they aren't commonly used by Amateurs, and so I won't talk here about them.

Ultra High Frequency (UHF) - 300 MHz- 3000 MHz- This band is the highest frequency band commonly used in Amateur Radio. It covers the 70cm, 33cm, 23cm, and 13cm bands. Of these, the most common by far is the 70cm, but 33cm, 23cm, and 13cm also have their following. UHF tends to penetrate buildings better than VHF, due to it's shorter wavelength which penetrates better. UHF is almost exclusively a line of site communication, while it will penetrate objects, it does not penetrate Earth, nor get reflected by the Atmosphere. It tends to be absorbed by moisture, and thus is affected by leaves significantly. This band is also home to many commonly used devices, such as WiFi, Coordless Phones, and other household items. Much analog TV transmission occurred on UHF. Commonly used for Walkie Talkies as well, due to the short size of the antennas required to make them work.

Very High Frequency (VHF) 30 MHz- 300 MHz- This band is very popular for Amateur Radio use, including the 6m, 2m, and 1.25m. Of these, the 2m is the most popular, but 6m has it's place. These frequencies commonly can talk beyond line of site, although not significantly beyond typically. The larger wavelengths start to exhibit the propagation characteristics such as ionosphere reflection, especially Sporadic E Propagation. VHF penetrates trees relatively well, but is mostly a line of site band as well. It is also known for FM broadcast radio, and is still used today for such purposes. I have made contacts as far as 70 miles or so away using VHF waves.

High Frequency (HF) 3MHz-30 MHz- This band is well known for it's propagation throughout the world. These waves actually are reflected off of the Ionosphere, producing a phenomena known as Skywave Propogation. Frequencies in this region include every Amateur Band from 10m-80m, I won't bother to list them all. It also includes CB radio, which allows for unlicensed communication at comparatively low power. I don't have a lot of experience yet, but I have heard conversations as far as half way across the United States in my very brief time playing with it, but I know people regularly talk across the world.

Medium Frequency (MF)- 300 kHz- 3 MHz- This only contains one Amateur Band, the 160m band. The primary means of communication with this band is Ground Wave Propagation, which has a fairly limited range. In general, the higher bands do well for communicating across a local area, while the higher bands do better for communication across the world. It should be noted that the first trans Atlantic communication via radio waves was done by Amateurs using MF. Commercial AM Broadcasting is done in this band.

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