When Gregg Hersholt signs off for the last time on KIRO FM at 9 a.m. on Friday just before the CBS hourly news (maybe, he says, with a snippet of the Grateful Dead’s version of “Not Fade Away”), he will have beaten his grandfather Jean’s tenure on the KIRO radio airwaves by nine years.

The elder Hersholt was a Hollywood film star who also played “Dr. Christian” on the radio program of the same name on the CBS network (carried locally by KIRO) for 17 years, from the 1930s to the 1950s. Grandson Gregg lasted 26 years at KIRO — a rare tenure at the same station — for a total of 30 years on the air in Seattle and 37 years broadcasting in the Pacific Northwest.

Hersholt’s departure announcement came earlier this week during the 5-9 a.m. morning news program he co-anchors from KIRO FM’s Eastlake studios along with Linda Thomas. KIRO FM owner Bonneville is making changes at the station, and the 58-year-old Hersholt’s dismissal likely portends even bigger shifts on the horizon.

The introduction last year of Portable People Meters (or “PPMs”) to measure the size of the listening audience has wreaked havoc on personnel at local radio stations, notably KING FM and now KIRO. Once a dominant ratings powerhouse with news, talk and sports at 710 AM, KIRO underwent a major shift last year; Bonneville moved news and talk to 97.3 FM (the frequency occupied for many years by oldies station KBSG) and turned its AM property into a sports-talk station. (Incidentally, thanks to various ownership changes, neither KIRO FM nor KING FM is affiliated with the Seattle TV stations using the same call letters.)

Whether because of the frequency switch, because audience habits have changed, or perhaps a little of both, KIRO has been hit hard by the PPM ratings, which tend to favor all-music formats such as Jack, Warm and Smooth Jazz. Lower ratings translate into less ad revenue and, ultimately, management not willing or able to spend as much on programming.

“Right now the stations that are rated the highest [by PPMs] are the ones that are basically automated and playing music,” Hersholt says. “They don’t have to go out and pay the high salaries for a big-time morning personality anymore. They can just roll the music and make money.”

Hersholt grew up in Beverly Hills in the 1950s and 1960s, when the Hollywood enclave felt like a “clean, small town that happened to be in the middle of L.A.,” he says. Like many a career broadcaster, early exposure to the radio industry hooked him. “I remember going to a radio station once with my dad, seeing the guy with the big voice, and thinking ‘that would be fun,’ ” Hersholt says.

After graduating from Gonzaga University in Spokane, Hersholt worked there at KJRB and then at stations in Portland before coming north to KJR in 1980. In those days of more rigorous FCC enforcement of public service requirements, and before ownership rules were relaxed, nearly every radio station was locally owned, and each had its own news operation. Even KJR, then in the waning days of the Top 40 music era, had a robust news operation with five employees, Hersholt says.

Prior to joining KIRO as Snohomish County bureau reporter in 1984, Hersholt also spent time doing news at KVI, when that station was still owned by Gene Autry’s Golden West Broadcasting.

Over his 26 years at KIRO, Hersholt has been a reporter, an in-studio news anchor, and a news program host. He spent a decade from the late 1980s to the late 1990s on the afternoon news anchor/host shift, and more than 10 years doing mornings, with its requisite early-riser schedule. “The biggest thing I’m looking forward to is not getting up at 2:30 in the morning,” Hersholt says, though even on the weekend he wakes exactly at 2:30 a.m. without an alarm clock. “I’ve got to get my body clock back to normal,” he says.

During Hersholt’s decade-plus of early rising, Seattle and other media markets have seen huge shifts in how and when media is consumed, and where advertisers direct their dollars. Blame it on iPods or the Web or whatever appliance you like, but local radio revenue is nowhere near what it was at the end of the 20th century.

“Think of the [local] morning shows that were on 10 years ago that are gone. No more Robin & Maynard, no more Charlie Brown. Those kinds of big, expensive shows aren’t around anymore for a reason,” Hersholt says.

In spite of the changes and the challenges, Hersholt believes that local radio can still be relevant in the future. “With the new ratings system, you’ve got to offer something unique and local that you can’t get on your iPod or your phone,” Hersholt says. “I’m still optimistic that there’s a place for personalities on the radio . . . I’m hoping there’s a place for somewhat intelligent discussion on the radio that isn’t all crazy, political extremism.”

A longtime West Seattleite, Hersholt’s married, with three grown kids and a young grandchild. He’s an active volunteer with the West Seattle Helpline and food bank, and with alma mater Gonzaga.

Hersholt doesn’t seem bitter about being let go by Bonneville, and he says he admires the company’s commitment to public service. But he also says he’s too young and has too much energy to retire. “I’m one of the truly fortunate people who had a long career doing what I love. But you haven’t heard the end of me. I’m going to explore what opportunities there are outside of radio. I’ll be around.”

But what about the great-grandchildren of “Dr. Christian” &mdash did any of Gregg Hersholt’s kids follow in their dad’s big-voiced footsteps?

“They all took my advice and did not get into radio,” Hersholt said.