Editing Very high frequency (section)

==Propagation characteristics==
Radio waves in the VHF band propagate mainly by [[line-of-sight propagation|line-of-sight]] and ground-bounce paths; unlike in the [[high frequency|HF]] band there is only some reflection at lower frequencies from the [[ionosphere]] ([[skywave]] propagation).<ref name="Seybold">{{cite book | last1  = Seybold | first1 = John S.  | title  = Introduction to RF Propagation | publisher = John Wiley and Sons | date   = 2005 | pages  = 9–10 | url    = https://books.google.com/books?id=4LtmjGNwOPIC&q=VHF&pg=PA9 | isbn   = 978-0471743682 }}</ref>  They do not follow the contour of the Earth as [[ground wave]]s and so are blocked by hills and mountains, although because they are weakly refracted (bent) by the atmosphere they can travel somewhat beyond the [[horizon|visual horizon]] out to about 160&nbsp;km (100 miles). They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause [[multipath propagation]], which can interfere with television reception.  Atmospheric [[radio noise]] and interference ([[radio frequency interference|RFI]]) from electrical equipment is less of a problem in this and higher frequency bands than at lower frequencies.  The VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for [[two way radio|two-way]] [[land mobile radio system]]s, such as [[walkie-talkie]]s, and [[two way radio]] communication with aircraft ([[Airband]]) and ships ([[marine radio]]).  Occasionally, when conditions are right, VHF waves can travel long distances by [[tropospheric ducting]] due to refraction by temperature gradients in the atmosphere.