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The ionization of the atmosphere varies with time of day and season as well as with solar conditions, so the upper frequency limit for skywave communication varies throughout the day. MUF is a median frequency, defined as the highest frequency at which skywave communication is possible 50% of the
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Another important parameter used in skywave propagation is the optimum working frequency (OWF), which estimates the maximum frequency that must be used for a given critical frequency and incident angle. It is the frequency chosen to avoid the irregularities of the atmosphere.
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of the ionosphere decreases with increasing frequency, so there is an upper limit to the frequency which can be used. Above this frequency the radio waves are not reflected by the ionosphere but are transmitted through it into space.
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On a given day, communications may or may not succeed at the MUF. Commonly, the optimal operating frequency for a given path is estimated at 80 to 90% of the MUF. As a
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layers of the atmosphere and return diagonally back to Earth. In this way radio waves can travel beyond the horizon, around the curve of the Earth. However the
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where the critical frequency is the highest frequency reflected for a signal propagating directly upward and θ is the
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86:(LUF) which is the frequency at which communication is possible 90% of the days, and the
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249:{\displaystyle \mathrm {OWF} =0.85\mathrm {MUF} =0.85f_{\mathrm {c} }/(cos\theta )}
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146:{\displaystyle {\text{MUF}}={\frac {\text{critical frequency}}{\cos \theta }}}
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radio communication, a major mode of long distance propagation is for the
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Highest radio frequency that can be used for skywave radio transmission
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that can be used for transmission between two points on Earth by
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386:"Lowest & Maximum Usable Frequency, Critical Frequency"
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93:Typically the MUF is a predicted number. Given the
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328:Practical antenna handbook, 5th edition.
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369:: CS1 maint: archived copy as title (
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104:the MUF is approximately 3 times the
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392:from the original on 18 October 2016
82:days in a month, as opposed to the
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88:frequency of optimum transmission
415: This article incorporates
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428:General Services Administration
352:from the original on 2012-02-08
295:Near vertical incidence skywave
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285:Lowest usable high frequency
84:lowest usable high frequency
467:Radio frequency propagation
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95:maximum observed frequency
163:Optimum Working Frequency
50:or skip) at a specified
28:maximum usable frequency
423:Federal Standard 1037C
417:public domain material
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436: (in support of
388:. Electronics Notes.
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69:to reflect off the
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157:angle of incidence
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128:critical frequency
106:critical frequency
334:978-0-07-163958-3
300:Radio propagation
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394:. Retrieved
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354:. Retrieved
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24:transmission
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438:MIL-STD-188
67:radio waves
452:MUF Basics
356:2012-03-14
44:ionosphere
40:reflection
241:θ
138:θ
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63:shortwave
56:shortwave
42:from the
461:Category
396:23 April
390:Archived
365:cite web
350:Archived
310:TV-FM DX
259:See also
316:Sources
280:F-layer
270:E-layer
90:(FOT).
71:ionized
48:skywave
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275:E-skip
419:from
290:MW DX
21:radio
398:2014
371:link
330:ISBN
209:0.85
192:0.85
52:time
132:cos
119:MUF
61:In
32:MUF
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