The term "Franken FM" was adopted sometime in the last decade to describe the anomalous analog Low Power Television stations licensed on analog Channel 6 frequencies (82-88 MHz). Because the aural carrier for NTSC analog televisions stations is located at 87.76 MHz, select Channel 6 stations in certain markets persist, purposefully opting not to transition to digital to specifically take advantage of using 87.7 FM as an FM radio station (rather than positioned as a television station). In the "old days", if you had a Channel 6 station local to you, you probably noticed if you tuned to the left end extent of FM dial you could hear the Channel 6 audio broadcasting at reduced 'volume'. In fact, these stations current "Franken FMs" actually are supposed to still supposed to broadcaster at a 'volume level' below regular FM stereo channels. The stations are actually breaking the rules (Sections 73.682 and 73.681) as currently stipulated (FM station may broadcast with +/-75 kHz deviation, and television is supposed to adhere to +/-25 KHz deviation). If you tune into these channel 6 stations on TV their audio is thus too overloaded for the TV tuner.
LPTV was never required to transition to digital broadcast like the rest of full power television licensees. However, the sunset date from analog broadcasting is currently set at July 2021 for converting to digital. Upon digital conversation, the aural carrier (the audio on 87.7 FM) would disappear. The owners of these stations often lease-out the audio portion to other organizations or businesses specifically for for these entities to operate as similar to full power FM radio stations. Because monthly leasing-out of these channels pull in profit for the licensee, LPTV licensees have motivation and money to lobby the FCC to try grandfather these 87.7 FM stations. Two entities in specific are at the forefront of advocating to keep retain analog 6 channels -- Preserve Community Programming Coalition, and Venture Technologies Group. Venture co-oped the business model of leasing out 87.7 FM channels going back over a decade. They originally attempted to procure as many as possible to specifically lease out. Most DTV broadcasters have abandoned using VHF 6 channels because channels 2-6 have undesirable background noise characteristics and/or the DTV does not propagate as well as UHF for the power levels suggested by the Commission for DTV use.
The Commission originally sought comment in 2014 concerning the feasibility of transitioning analog channel 6 stations to digital, but allowing an analog carrier on 87.7 FM (via 87.7 FM only broadcasting in vertical polarization). It is not even clear if this is legal under the FCC rules (Section 336(b)(1) of Communication Act). The FCC did not take up the issue in 2015, but now with pro-business Commission they appear to be accepting comment on actually extending 87.7 FM into the digital age.
If there is one party completely against prolonging 87.7 FM broadcasts, it is KKJZ 88.1 FM Long Beach, California. KKJZ operates second adjacent to Channel 6 KZNO-LP Big Bear, California, for which they assert is an interference concern. Alfthough KZNO-LP sounds like a rural station, it serves the Los Angeles basin from Mt Hamilton on 87.7 FM, which is considered quite an asset for its licensee Venture Technologies. The Los Angeles channel is leased to Radio Guadalupe. Venture also has a few strategically-placed analog channel 6 stations, such as in San Jose, California (KBKF-LP), which is leased by KLOVE, and in Chicago, Illinois (WRME-LP), where ME TV runs an oldies format that actually shows up in the local radio ratings. Perhaps the most popular 87.7 FM, second to WRME-LP, is WNYZ-LP in New York. This station operated as Pulse 87, a dance station (2008-2009), then Party 105, a few other niche formats for stints, then finally settling on a Korean language format in 2010. In 2016 it was purchased by NY Metro Radio Korea for 1.8 million dollars. The most DIY-implementation of a Franken FM is in Sacramento, California where a channel is leased to a community broadcaster (whose manager used to participate with KPFA) from midtown Sacramento with this retro html website.