RFree - more than a channel finder!

We are very excited to announce the public launch of the beta version of Rfree, a free and open source software for LPFM community radio applicants and the engineers developed by Prometheus Radio Project.  This web-based software offers technical support for Low Power FM (LPFM) applicants.


Check out the RFree user guide and RFree Videos. Click in the image below to access manual.

In order to be eligible to apply for a LPFM license, there must be an available channel in your proposed area of transmission.  Rfree will allow you to do a preliminary study of the availability of frequencies in your community and give you further information on the coverage area, interference levels, and spacing to other channels.  In other words, you’ll be able to see clearly what’s available on the radio dial and what the possibilities are for potential frequencies in your city or town.

Rfree frequency searches will show users a tri-colored chart of channels that have various levels of FCC application difficulty (Green=easy, yellow=possible, and red=impossible but worth investigating). As a result, not all available frequencies shown to be available comply with the rules defined by the FCC in the same manner; you may have to work with an engineer to prove that your frequency will not cause interference to other existing stations.

Logging into Rfree:

To get started using Rfree users must first create an account on RadioSpark.org, an online portal created by Prometheus Radio Project with the intention of providing guidance and support for applicants of LPFM licenses. Once logged into RadioSpark, users can access Rfree and start their frequency search. You can access through the link in RadioSpark http://rfree.radiospark.org/ or through our discussion forum  in http://radiospark.org/rfree

Click the RFree button on the right to use the software.  No Rfree Button?  Log in first or get an account with the Join box (on the right) or the new user account form.  Scroll down on this page if you have RFree Questions, want to learn what it can do, or join the discussion.













Because Rfree is linked to users’ RadioSpark account, the software will allow them to save their frequency searches for various locations. Users will be able to retrieve past searches and compare results saved with their profile.

By creating an account on RadioSpark users are making their information available to Prometheus so that we may be able to support applicants throughout the application process. RadioSpark is an open and accessible forum for community radio applicants. Participation will grant applicant groups the opportunity connect with engineers, community radio novices and experts to ask questions, share resources, and connect with allies. Once you have created an RadioSpark account you can access Rfree!



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FCC Awards

So, guess I've missed this answer researching online - So after you submit your application to the FCC for your LPFM, when should we hear something back positive or negative?  If there's any mistakes that slipped through after validation will they tell you about it in time?  Or when there's a challenger for your requested frequency will they inform you?  Waiting with anxious breath in Ohio...



Baton Rouge Louisiana

Hey Paul I have watched all the youtube videos you have posted on youtube.  I had a question about the quick and easy waiver.  I ran the channel search for Baton Rouge, LA and it shows that 102.1 is in yellow with a PZ of 13.  Can I use the exhibit that Rfree produces giving that the PZ is low.  I just want to know if that exhibit is enough giving that the PZ is only 13.


RFree 2nd adjacent exhibit

In theory yes -- if you went through the decision tree and after very carefully reading the exhibit, primarily the third paragraph, it is definitely true for your situation, then you should be able to use it -- that's what we built RFree to do ultimately.  If you are at all unclear on anything, or even if not, I recommend that at least one other person look it over with you.

The PZ (aka D/U) exhibits have two vital components -- first is the technical calculation of the size of the interference zone, which you should not need to change.  The second is the argument in paragraph 3 that there is and will be "no population" within the interference zone, which is a precedent-based standard.  If anything is at all vague about your situation then it may be prudent to have a lawyer or engineer consult on that part.

Lloyd Ewing

Discrepancy in Austin

96.1 MHz shows up as a green "definitely available" frequency on RFree, but it does not appear at all on either MyLPFM.com or the FCC channel finder. Is this just a difference in search settings or is something wrong? This is an example: (79.7W@34m) 15m antenna height 30 23 23.64 N 97 42 15.28 W ...Thanks very much!

Discrepency due to late-filed translator changes

It's a great idea to compare the three channel finders, and this shows why!

RFree gets this one wrong so I'll be fixing it shortly.  And this also is bumping up against an area where I don't think there's a consensus as to what is "right".

The FCC excludes 96.1 and I'm sorta guessing their channel finder might be accidentally correct rather than purposefully correct.

myLPFM gets it right, and I'm guessing it is purposefully correct because I've come to expect that from myLPFM.

The back story is that RFree sees K242CC, as you can see on the 96.1 page in RFree in Austin, as resulting from changes filed after the June 16th deadline, because the associated application is dated July 25th.  If that had been a MODIFICATION application, RFree would be correct.  But it was a license-to-cover where the respective modification app was filed early enough so that it needs to be protected.  This is going to get worse as CDBS continues to churn.  Translator modification authorizations filed after the 16th are being issued with conditional language stating that LPFM awards might invalidate those changes, so RFree is attempting to show opportunities like that.

Stay tuned...



RFree 1.0.1 now matches results with myLPFM for Austin and I think the change is cautious and for the better, however due to several factors including 1) some FCC procedural/policy unknowns 2) the ongoing churn in CDBS and 3) the structure of CDBS particularly fm_eng_data table; I believe that /every/ channel finder is giving both false positives and false negatives in certain situations.  I think "quagmire" might become an apt description of what's happening.


Elevation AMSL/Antenna Height/HAAT Calculation

I like the overall "feel" of RFREE, and is as good or better than myLPFMSearch. There is one bug in the software: Calculating HAAT/ERP with a known Ground Elevation AMSL and Antenna Height. One proposed station I plugged the data into had a Ground Elevation AMSL of roughly 320m, and the Antenna Height was 24.0m above ground. I ended up getting 1 Watt ERP at 354m HAAT!!! The surrounding terrain was not THAT mountainous based on my surveys around the area. Using the same Ground Elevation and Antenna Height data in myLPFMSearch, there was a HAAT of 32m with 85 Watts ERP, which sounds more reasonable. I realize this is a beta version, so I thought I'd let you know about the glaring discrepancy so it can be put on the "Things to Fix" list. :-)


double-check FCC's HAAT

Would love to have the lat/lon of this location as amartina suggested.  Also it is easy to check the HAAT via the FCC's HAAT calculator at http://transition.fcc.gov/mb/audio/bickel/haat_calculator.html and that is the same source RFree uses (and possibly uses in a buggy way!).  My email is pbame-at-prometheusradio.org


Reply to double-check FCC's HAAT

I see there has been an update to the RFree software that has a more realistic calculation of HAAT based on geographic coordinates and Antenna Radiation Center AGL. Here is the coordinates I was using for the two original locations:  42 25 36.46 N,  88 36 1.39 W and 42 9 47.42 N,  88 25 46.37 W. I was getting triple digit HAAT when I originally used RFree, but now it shows me a -10 meter antenna height for 100W/30m HAAT on the first site. Plugging in the antenna height of 28.0 Meters yields 19 W/68m HAAT, which was calculated in myLPFM. The second location calculation shows 20 meter antenna height for 100 W/30m HAAT, and looks more like what I was expecting. I like the added feature of suggested 50 watt, 25 Watt, and 1 Watt levels. This helps to "adjust" antenna heights with instant results of what the Watts/HAAT will be. Thanks for the quick response to this bug fix!

Robert P. Yeoman, Broadcast Techinical Consultant



Thanks! We will add t to the bug list. if you find any other bug, please let us know. Also, was wondering if you can pass along the location where you found that discrepancy, that way we can simulate the case. Are you working with other softwares or mostly looking for the antenna allocation? If you have engineer background skills it would be good to have some help in the bug report. Thanks!!!




A new set of bugs in RFree

Was checking previous Location data that was stored with the correct listing of antenna height and ERP/HAAT, but when I go back to the Height tab, it now shows a single digit ground elevation and a 3 digit Antenna height. I also see from the summary that the signal coverage is a perfect circle, whereas before, it appeared to show coverage based on ground level contour. There was a recent period a week or so ago where I could not start RFree, and got several lines of machine language on the screen. Just wondering if something happened? And now in light of 3,000 FM Translator Applications being dismissed by the FCC Feb. 5, 2013, that will change a goodly part of the FM database. Thanks for your help!

Robert P. Yeoman


Discrepancies between RFree and RECNet LPFM Channel Search

What are the reasons for descrepancies in results between RFree and the LPFM Channel Search on RECnet? Where does one go in terms of judging availability in such a case? 

Here is one example. Searching for 42.3049172, -83.1916937 (latitude and longitude) will result in two second adjacency frequencies in RFree and none in RECNet. 

Thank you!



REC/myLPFM, RFree, and also the FCC channel finder, are all going to give different answers once in a while.  The complexity of FCC rules, database, interpretation, and each software's interpretation and implementation of the LPFM rules nearly guarantee this unfortunately.  It is REALLY GREAT for me, as an RFree developer, to know about these discrepencies because deeply understanding them is going to improve RFree and possibly the other channel finders too.  So keep those discrepencies coming!

RFree now offers users a one-click way to search the same location via myLPFM or FCC -- see the links at the bottom of the channels-available page.


It is an useful information

It is an useful information for all those who like to have the LPFM license. The procedure seems to be different and really easy . I have taken down the procedure and made a note of it . Thank you for the set of data that have been shared online about rfree sites.



About RFree

RFree is free and open source software for community radio applicants and the engineers who support them. RFree helps users find available channels and gather information for their FCC applications. Currently, RFree supports two station classes: 100 watt low power FM (LP100) and 10 watt low power FM (LP10). 

RFree is primarily being developed by the Prometheus Radio Project. It draws on the prior work of many other individuals and organizations, most notably REC Networks, Al Davis, and the FCC.

RFree is free and open source software licensed under the GNU Public License. This means that anyone is free to use, copy, modify, or redistribute it. Free and open source software has many of the same benefits as community media: it is easier to access, more transparent, and easier to change when needed. If you are interested in contributing to RFree, we encourage you to check out the project wiki and/or browse the source code at http://www.hostedredmine.com/projects/rfree.

In order to run properly, RFree needs a database of information from the FCC. While anyone could set up their own server to run RFree, Prometheus hosts an instance of the software that all RadioSpark members can use. To use RFree click the "RFree" button on the right and try it out! (You must be logged into RadioSpark.)


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