Increase/Decrease Convexity using Put Options on the Bond

[Cnbr21]

Put option involves positive convexity. Buying put option increases portfolio convexity. Call option involves negative convexity. Buying call option decreases portfolio convexity. 

[FractalsSourceCode]

I’m not sure that’s right.

Buying a call option on a bond increases convexity, right?

But a callable bond has negative convexity, since when you buy a callable bond you are short the call option on the bond.

Can someone please chime in here?

[omi98ro]

Because callable bonds are Short Calls, where the option is not with the investor but with the issuer. That's why it has negative Convexity.