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Prometheus Radio Project
Version 2.6


Please read the following notes before using RFree.

  • This software is for planning purposes only. The Prometheus Radio Project does not guarantee the accuracy of the information presented in RFree. This information is based on interpretations about the FCC's rules for Low Power FM radio, which are subject to change. Additionally, some known rules are not yet implemented, and there may be errors in the implementation of known rules. Do not use data from RFree when filing an FCC application without confirming your results elsewhere.
  • The Prometheus Radio Project will not sell, rent, exchange, or otherwise disclose personal data without your permission, but cannot guarantee the privacy and security of any data entered in RFree. Prometheus may disclose bulk data, such as the total number of users, the number of available channels uncovered, or the number of searches performed in a particular zip code.
Recent Changes
  • 2.0pre2 - Feb 2018
    • Upper-left summary, for modifications, shows the original and relative distance and channel changes
    • Delete/Copy buttons now in Change-Location menu
    • Height page can change ERP down to 50%
    • Height page dynamically calculates PZ, ERP as antenna height or elevation changes
    • Channel Details page format and brevity by default
    • Channel Details page allows some dynamic sorting and selection
    • Station pair page improved and a bit more mobile friendly
    • Lazy evaluation increases speed a little
    • GUI changes inside and out
  • ...many undocumented revisions...
  • 1.9pre4 - Dec 2015
    • Saved LPFM searches are matched by Station/Applicant Search.
    • Saved LPFM searches are present in channel details pages.
    • Odd formatting on google maps is fixed.
    • LPFM searches copied from CDBS LPFMs now show the minor-modification (6.4km) area on maps where they can be moved.
    • The above minor-modification circles on the map are accurate according to the (required) FCC FM distance formula and inaccurate according to all other formulae used by geographic software and the FCC.
  • 1.9pre3 - Oct 2015
    • Personal searches are included with More...->Station/Applicant Search and "Details for Frequency"
    • Longley-Rice-based clear-signal distances are now shown in addition to those based on the FCC Contour method.
    • Interference and service contours are now correct to within 1 meter of the distance as measured by the FCC FM distance formula
      The normal method for calculating a coordinate at a specific azimuth and distance from another coordinate is based on some variation of of a great-circle formula, including the algorithm used by the FCC (see the FCC SPRONG web page. The distance between these two coordinates will not agree with the distance produced by the formula required by the FCC for FM distance measurements, which sometimes produces erroneous results for interference compliance and for maps showing areas to locate based on drawing spacing circles (these latter have not yet been corrected fully).

      Correction requires a combination of iterative coordinate correction, and careful consideration of when to convert between NAD83 and NAD27 coordinates.
    • NAD coordinate conversion is now done with custom software rather than the PROJ.4 cartographic software. ?>
  • 1.8 - March 2015
    • "What-if" frequencies available (expand bottom of frequencies available page)
    • Increased precision (shown) of HAAT and PZ
    • When viewing CDBS LPFMs, can check if FCC calculated HAAT wrong (see review->overview)
  • 1.7 - After the first FCC MX Tentative Selectee Public Notice
    • Many functions available without logging in
    • Menu re-structuring and station search page as default
    • Can now parse coordinates like 30-30-30 N 30-30-30 S
    • Update to new USGS elevation service
    • Daily CDBS updates
    • Improvements in login/logout processing
  • 1.6 - Immediately after LPFM application window
    • Station/applicant listings show application status
    • "Late-filed" translator changes now affect channel availability
    • More FM allocations are protected
    • Estimate which translators and LPFMs might be able to infringe on a particular location/frequency with new menu [Frequency...->Competitors]
    • View MX maps and locate LPFM applicants for study and major/minor modification evaluation via menu [more...->LPFM Station Search]
    • Using FCC Fortran field strength calculator instead of FCC's C-language one due to inaccuracies in the latter
    • On "Availability Map" pages, can disable the spacing circles corresponding with MXed LPFM apps and ungranted singleton apps.
    • Check if registration needed for antenna tower with menu [Review...->TOWAIR]
    • Find out more about stations via both FCC CDBS Application Search as before, and also by Station Search. When likely, the "318" link also gives rapid access to a local copy of the applicant's "318" form (new LPFM apps only)

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