Shares in Capital Radio-owner GCap Media have plunged by over 17% after it reported lower profits and unveiled a plan to cut the number of ad breaks.
GCap hopes fewer ads will mean more listeners
Underlying half-year profits at GCap, which also owns Classic and Xfm, fell 28% to £12.4m ($21.3m).
GCap chief Ralph Bernard said the results were "extremely disappointing".
The group said it would cut the number of adverts on its flagship London station Capital in an attempt to stop people switching to rivals.
It said it would not broadcast more than two adverts in a row on its flagship Capital station, and would reduce the total number of adverts broadcast.
GCap is not planning to raise prices to compensate for the reduced advertising, and, as a result, revenues for the station are expected to be £7m lower in the 2006/07 financial year.
However, GCap said it regarded the fall in revenue "as an investment for the longer term".
At the close of trade on Thursday, GCap's shares were down 59 pence, or 17.3%, at 283p.
Revenues for the six months to 30 September were down 11% to £111.6m.
"These results are extremely disappointing, and I believe in no way reflect the full potential of the portfolio of assets owned by the group," said Mr Bernard.
"We are taking firm management action to improve them," he added.
In addition to the change in advert policy, Capital Radio is due to be relaunched on 3 January with new music and new branding.
In the past four years, listener figures at Capital FM have fallen from 2.9 million to 1.8 million, while its London audience share is down to 5.1% from 10.9%.
GCap said it would also be selling nine of its smaller analogue stations, including Orchard FM, Plymouth Sound and Coast FM.