The Blues have suffered losses to Glasgow Warriors and Ulster Rugby at BT Sport Cardiff Arms Park in the last two weeks and face a difficult challenge as they travel to PRO12 champions Leinster on Friday evening.
The Welsh side have conceded more than 30 points on each of their last five visits to the RDS but Turnbull is confident his team are capable of reversing the trend in Dublin.
And the 26-year-old, who joined from Scarlets in the summer, insisted there were plenty of positives Cardiff could take from their recent defeats.
"We are getting better each week," he told Wales Online. "Our scrum and driving line-out is going well and in the second half against Ulster we played off quick ball.
"We are creating opportunities in the opposition 22 and spending time in that area, so it is frustrating when you don't get the rewards.
"Our defence at times was superb - some massive hits went in. We have got to build on that.
"But we know we weren't clinical enough and didn't play in the right areas of the field at times. We're conceding easy points at times and that's frustrating.
"It's never an easy game when you play in Leinster. The RDS is a tough place to go, especially when the crowd gets behind them and their ball-carriers get on the front foot.
"They go out to express themselves, but we will look at what they do and what we can do."
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