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Why are the VHF bands closed every day? Is it getting abandoned? Every time I check the solar conditions, it says that the VHF bands are closed. GlobalNorth says, "As the big public safety and corporate users migrate to 700+ MHz and abandon VHF high and UHF, the smaller users are adopting VHF/UHF higher frequencies to avoid the elevated noise levels of low band." So, is there a chance of VHF opening?

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  • $\begingroup$ Specifically, which VHF bands did you have in mind? $\endgroup$ Commented Apr 27 at 22:38
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    $\begingroup$ I feel as though you know this, but I just want to be sure... You realize that "closed" doesn't mean that you can't use them.. it means that the noise floor will be high and propagation is very poor... $\endgroup$
    – David Hoelzer
    Commented Apr 27 at 22:59

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Solar cycles have almost nothing to do with corporate use of VHF bands. Solar activity is very irregular and corporate use of bands want something that is reliable. Likely corporate users are migrating to higher frequencies because of increased bandwidth available and smaller components made possible by shorter wavelengths, and this has nothing to do with solar activity.

VHF is largely line of sight propagation, which does not rely on solar activity, and noise from solar activity is rarely bad enough to significantly degrade this.

On the other hand, in rare conditions, high solar activity could pump the atmosphere to the point where there is some ionospheric reflection into vhf frequencies, and amateur radio operators can take advantage of this. However, more common place events like ducting (which can be annual) has a much larger effect on VHF.

Solar activity maps that talk about bands being "open" or "closed" are really trying to gauge conditions of bands with longer wavelengths that easily reflect off the ionosphere, mostly longer than 10m. But since there are rare occurrences of shorter wavelengths also being affected, they are listed in the graphs and maps. Even these longer wavelengths can be used when they are "closed" through groundwave propagation (just like VHF), although they may also be more susceptible to noise, including lightning storms and solar noise.

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