A Canberra man who blackmailed a senior detective over a building job gone sour will spend his weekends behind bars for the next six months.

An ACT Supreme Court judge on Thursday described Michael Brian Pearce's demands as threatening and ''verging on the bizarre''.

But Justice John Burns accepted the 49-year-old was remorseful for his actions and had since taken steps to address his alcohol abuse.

The court heard Pearce's harassment began with thinly-veiled threats about Victorian planning authorities and escalated to threats of grievous bodily harm.

At one stage he intimated he was part of ''Mokbel's mob'', ostensibly a reference to jailed drug kingpin Tony Mokbel.

The detective sergeant hired Pearce in October last year to replace the front porch of his Melbourne home.

He sacked him three days later because he wasn't satisfied with the quality of the work.

Pearce then started sending angry text messages to the policeman's phone, telling him to pay him $1500 for the work.

He threatened the man with bankruptcy, said it would be ''VCAT [small claims tribunal] and ur demise'', demanded an apology and asked him if he wanted to ''go down big time''.

In March Pearce, then living in Canberra, called the policeman twice on the same day claiming to belong to a ''syndicate''.

Pearce demanded $50,000, saying he was ''one of Mokbel's dudes'' and the man and his wife would be ''vegetables'' if he didn't pay up.

Pearce was recorded asking the policeman, ''Do you reckon I'm stupid? Do you think I'm a petty criminal?''

The policeman asked where he was supposed to find the $50,000 and Pearce told him to get it or ''your f---ing wife drinks vegetable soup''.

Pearce was arrested in April after the policeman alerted his territory counterparts.

Justice Burns noted Pearce's demands ranged from first $50,000, to $100,000 and then $50,000 a day. ''The pattern of those demands verged on the bizarre,'' the judge said.

He said statements from the victim and his wife ''spoke of the uncertainty your actions created, the fear created in your victims for themselves and their families, and also their continuing distress''.

The court heard Pearce had struggled with alcohol abuse since 2005 but in July this year checked himself in to a detox clinic at the Canberra Hospital.

Justice Burns took into account the man's remorse, plea of guilty and his efforts to rehabilitate.

''I accept that very little by way of planning was involved and you appear to have had no realistic way to collect money from your victim,'' he said. ''I accept [lawyer Anthony] Hopkins's submission that this was no normal blackmail offence.''

The judge noted he called an experienced police officer from his mobile phone.

''Even a moment's thought would have made it obvious that police would inevitably suspect you as the offender, which in fact occurred,'' Justice Burns said.

The judge sentenced Pearce to two years, to serve six months in weekend jail and the remainder suspended on entering a three-year good-behaviour order.