Former communications minister Stephen Conroy wants NBN Co to track down anonymous staffers who attacked him in the media.

Senator Conroy defended his ministerial legacy during a Senate committee hearing into the National Broadband Network in Sydney on Wednesday.

He took NBN Co executive chairman Dr Ziggy Switkowski to task over a February newspaper story which cited unnamed NBN Co sources blaming him for problems with the interim satellite service, specifically the changing of eligibility criteria for subscriptions.

Senator Conroy asked if it was the job of NBN staff to blame members of parliament for problems.

"I'm wondering what you're going to do about your staff behaving, in what ... is a fairly unprofessional manner?"

Dr Switkowski said Senator Conroy's concerns were well placed and that any off-the-record briefings by staff to journalists were inappropriate.

But he has not initiated any enquiries into the article.

"Trying to track down the source of unattributed comments tends to be a fruitless task," Dr Switkowski said.

The hearing was told the satellite service has reached its cap of 48,000 customers and that some were experiencing slow speeds because of high traffic.

An estimated 250,000 customers are eligible to receive the service but extra capacity is needed.

Senator Conroy said the timing of the cap being reached had been expected for several years.

There have been problems with congestion of the satellite service in Victoria, NSW and southeast Queensland.

NBN Co was fine-tuning engineering parameters to make the existing spectrum purchased more efficient, the hearing was told.

Communications Minister Malcolm Turnbull is aware of the capacity issue but has not asked NBN Co to acquire additional bandwidth, Dr Switkowski said.

Discussions are underway with suppliers but it's a matter for government, he said.

Senator Conroy said if the Abbott government was prepared to spend $200 million capacity could be increased significantly.

The hearing continues.