you can't , not you can trust anyhow . Only if it is a trusted manufacturer . Too Many aftermarket crap dealers on ebay . Claim their product to be on thing and it is really crappy . There are trustworthy dealers out there that give you real numbers . Stay away from brands such as Cell-gear . Trusted names are Cyfre , Wilson, Antennex , Laird to name a few.
said by angry :
may be a dumb question but where can i get ratings on dual band antennas?