There can be more than one VOR with same frequencies. It is important to have some minimum differences between their locations. This difference in location should be objective instead of subjective methods. To avoid dilution of accuracy, signals or authenticity of data provided by VOR system of standard service volumes was established.
SSV -Standard Service Volume defines the reception limits of unrestricted NAVAIDs which are usable for random/unpublished route navigation. SSV limitations are not applicable to published routes.
VOR/DME/TACAN Standard Service Volumes
|SSV Class Designator||Altitude and Range Boundaries|
|T – Terminal||From 1,000ft above ground level up to and including 12,000 ft AGL at radial distances out to 25 NM|
|L – Low altitude||From 1,000ft AGL up to and including 18,000 ft AGL at radial distances out to 40 NM|
|H – High altitude||From 1,000ft AGL up to and including 14,500 ft AGL at radial distances out to 40 NM. From 14,500ft up to and including 60,000ft at radial distances out to 100 NM. From 18,000ft AGL up to and including 45,000ft AGL at radial distances out to 130 NM.|
NDB Standard Service Volumes
|Compass Locator||15 NM|
Letter ‘W’ is used with class designator is no voice message in superimposed on navigation aid.