Digital antenna

[Observer]

Hi, I've just ordered a digital TV booster antenna which needs to be powered either 12v or 5v. In the description some of which is below it mentions a 5v active feed. Coming out of the rear of my stereo head unit are two (unused) wires one labaled Key1 5v and the other Key2 5v. I have contacted the vendor and asked if either of these could be used to provide the required power. He replied that that he thought the power would need to feed through the center of the coaxial cable via it's SMA plug. Would anyone know that if I have these two 5v wires, is it likely that the centre of the SMA plug would also be 5v?
Cheers in anticipation
Pete

Internal High Quality Car Digital DVB-T TV And FM Antenna
Frequency Range: 48.5 - 223 MHZ 170 - 230 MHZ 470 - 860 MHZ
SMA Or F-Type Antenna Connector
Dual (5V Active Feed & 12V Booster) Voltage
Twin Amplified Blade Technology
Suction Pad Installation Or 3M Fixing Pad
5m Extension Cable