In 1973, Jonathan L left New York and headed for Berkeley, California. He fell ill when he and his wife stopped to visit friends in Tucson, Arizona, and they ended up staying there for the next thirteen years. He began self-publishing a monthly pop culture magazine called Newsreal. The publication was known for its eclectic mix of music artists, putting such stars as Joan Jett and B.B. King on the same cover. Begun in 1974, Newsreal’s circulation reached 20,000 before the publication folded in 1985.

While on a summer hiatus in 1978 in New York City, Jonathan L was the Editor for two issues of Drugs & Paraphernalia Digest, with the former publisher of High Times magazine.

Jonathan L's radio career began in March, 1982 in Tucson, Arizona at 96 Rock KLPX with his creation, "Virgin Vinyl." The show ran for more than four years on Sunday evenings for five hours from 7 p.m. to midnight. Among the many live guests were Henry Rollins as a co-host, Joey Ramone, The Circle Jerks, Huey Lewis, and the Meat Puppets. The music encompassed everything from Metallica to Leon Russell.

In the summer of 1986, Jonathan moved up to Mesa, Arizona to start up alternative station KEYX 100.3 with his friend John "Johnny D" Dixon, referred to as "the key to your musical Future." The station ended in late 1987. Many felt it was far too ahead of its time. Jonathan was the assistant program Director and music Director, and held down the 7 p.m. to midnight shift Monday though Friday.

In 1988, Jonathan L was hired by Phoenix rock station 98 KUPD, where he hosted "Virgin Vinyl" on Sunday nights until 1992. The show, which included everything from Suicidal Tendencies to a then-unheard band named Nirvana, was a huge hit in Phoenix, and garnered several “Best Radio Show” awards from the Phoenix New Times, which called Jonathan L “a thoroughly modern mouthpiece” who played “forward-looking wax attacks.” In 1986, they wrote of “Virgin Vinyl”: “When this colorful Sunday night waxfest was imported from Tucson this year, it slapped the lethargic Phoenix radio market right in the face.” Simultaneously in 1989, Jonathan L founded and became program Director for KUKQ AM, Phoenix’s first all-alternative music station.

In 1989, Jonathan L organized one of the first large-scale radio festivals in the United States, for KUKQ. The bill included the Red Hot Chili Peppers and Camper Van Beethoven. Subsequent KUKQ festivals (there were two each year) included artists like Social Distortion and The Meat Puppets (1990), Mojo Nixon and Dead Milkmen (1990), and Rollins Band and The Sugarcubes (1992). His festivals received national recognition in 1991, when MTV filmed its popular alternative music show 120 Minutes at that year’s KUKQ Q-Fest, which included Front 242 and The Sisters of Mercy.

Jonathan L appeared on A Current Affair with Maury Povich in 1991, where he interviewed One Foot In The Grave, “the world’s oldest punk rock band,” a group from Sun City, Arizona with members all over the age of 60. In 2001, Jonathan L appeared on MTV2 in a 23-minute video feature about German rock group Rammstein.

He left KUKQ in 1992 to work for station KFMA in Wickenburg, Arizona. After a short stint there, he returned to KUKQ to retake over the helm as program Director and again did his show "Virgin Vinyl" until he left in 1993 to join Phoenix station KDKB, where he did his award-winning "Virgin Vinyl" until 1995.

He once again returned to KUKQ from mid-1994 to mid-1995 to run the station in its wildest punk rock form. Among his most popular programs was “The Monday Morning Music Meeting Live,” which gave listeners a chance to phone in and provide their own input on the music, which was added to the rotation that day.

In the fall of 1995, Rosen left Phoenix (and radio) to accept an opportunity to become senior Editor of the long time, now defunct, music industry trade publication the Album Network. He took control of "Virtually Alternative" magazine, one of many music format magazines the Album Network published.

In 1999, Jonathan was given Vice President stripes as SFX (and later Clear Channel) bought the Album Network and all its properties.

In 2000, at a convention Album Network put on in New York city dubbed Y2K, Jonathan organized and hosted a panel of Musicians to speak about everything from their careers to their personal lives in front of a packed house. The guest speakers were Ronnie Spector (The Ronettes), Glenn Danzig (Danzig), and Dee Snider (Twisted Sister). Jonathan was friends with Spector and Danzig, and thought they had more appeal and more to offer than many of the available alternative artists of that time period. Joey Ramone, also a friend, was the confirmed 4th panelist, but fell ill and couldn't make it.

After more than six and a half years, Rosen left the Network Magazine Group in 2002 to launch his own independent record promotion company which he operated until 2005. In the summer of that year, Rosen decided to leave Los Angeles and go back to radio, this time to do "Lopsided World Of L" at KUPD-FM in Phoenix.

In addition to his work on terrestrial radio, Jonathan L has also hosted several Internet radio shows, including a two-hour special for WOXY in Cincinnati in 2003, which included an on-air phone call from Jonathan L’s close friend, music legend Ronnie Spector. In 2000, Jonathan L hosted and programmed the weekly Sunday afternoon show “Pleasantly Annoying” for Hollywood, California-based SpikeRadio.com.

In August 2005, Jonathan L returned once again to 98 KUPD, where he hosted and programmed “The Lopsided World of L” on Saturday mornings and Sunday nights in prime time live. Jonathan L remained there until his retirement from stateside radio in 2010.

Back in 2007 when he was doing the show live on 98 KUPD FM in Phoenix the radio station starting streaming anywhere in the world. Jonathan had already made many friends and contacts from Europe and other countries and was promoting the show on Myspace. He used those contacts and new ones he made on Facebook in hope that if he was to use the internet, maybe that would give the show an edge and garner new listeners.

Then the break came in October 2010 when Los Angeles station Indie1031 asked him on. That was followed in December 2010 by German internet station KING FM also wanted Lopsided World Of L which was followed by Phoenix, Arizona's KWSS FM 93.9 and others from Greece, Romania and Gothenburg, Sweden (the latter three are no longer on-air). The show lasted five years on KING FM until the station went dark

From 2011 to 2014 he spent the better part of three years going to school three nights a week to learn the German language.

2012 Spontaneous self spoken voice tracks in-between all songs on Grand Duchy (band) album “Let The People Speak” by Black Francis of the Pixies and wife Violet Clark. Sonic Unyon Records (Ontario, Canada) Track #1 “The Lopsided World Of L” intro to album by Jonathan L and Black Francis on Keyboard

Jonathan L left his parents' Long Island home at age 14 and lived as a street urchin with a gang of juveniles. After quitting school and being convicted of assault charges, he spent three years incarcerated in various Juvenile institutions. He was out and on parole shortly before his 18th birthday, and took a job as a parts man for Mack Trucks. He also began writing for an underground newspaper in Long Island called The Express.

Wrote and voice/sang lyrics Music written by Barry Snaith (The Inconsistent Jukebox Wakefield/Leeds, England) Released July 2016, on Emerald and Doreen Records (Germany)

In describing the show he feels nowadays that is not an ‘Alternative’ one but more of a progressive free form entity in all styles of music featuring new artists and many older ones that re-enter with new music.

As the years go by he made many contacts directly with Musicians and record promoters from so many Countries that the show is mostly music that American stations and ’Specialty Show’s’ do not play. He feels that sets Lopsided World Of L apart from all the others.