The diode you show is a special type.
It is a so called varicap diode.
It is mounted in reverse and uses the voltage across the diode to control the capacitance.
Attached you will find two datasheets.
an AM varicap diode BB212
AND a small signal diode 1N4448
I showed you the two datasheets to see the difference between the varicap and a conventional diode.
The BB139 will have a capacitance curve in reverse mode.
The capacity will be lower as the BB212 as the BB139 is for VHF and the BB212 for AM.