Editing Critical frequency (section)

== Critical frequency and the F layer of the ionosphere ==
* All long-distance HF radio communications use HF radio signals that are obliquely incident on the ionosphere. If the HF frequency is above the critical frequency, the radio signals pass through the ionosphere at an angle instead of head-on.<ref>{{Cite web|url=http://www.sws.bom.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Intro%20to%20HF%20Radio.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.sws.bom.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Intro%20to%20HF%20Radio.pdf |archive-date=2022-10-09 |url-status=live|title=HF radio propagation|website=Space Weather Services}}</ref>
* The critical frequency changes continuously and the [[F region|F layer]] of the ionosphere is mostly responsible for the reflection of radio waves back to Earth.
* The other layers(D) interact in other ways - absorption of frequency and during the day, the D Layers forms, and the F layer splits into F1 and F2 layers.
* Because of changing the Ionosphere during day and night,  during daytime higher frequency bands under critical Frequency work best, but during nighttime the lower frequency bands work best.
* The D layer is present during the day and it is a good absorber of radio waves, increasing losses, Higher frequencies are absorbed less, so higher frequencies tends to perform better during daytime.
* The actual F2-Layer Critical Frequency Map link which refreshes every five minutes can be seen in this website http://www.spacew.com/www/fof2.html {{Webarchive|url=https://web.archive.org/web/20140628231212/http://www.spacew.com/www/fof2.html |date=2014-06-28 }}
* The Ionosphere and the Practical Maximum Usable Frequencies (MUFs) Map link which refreshes every five minutes can be seen in this website http://www.sws.bom.gov.au/HF_Systems/6/9/1