Just take a Portfolio of at least 25-30 different receivables. The goal is, to elminate the single risk of each item in the portfolio (individual risk – ALPHA). The risk that is left over is the market risk (BETA). Its dimension depends like risk in general on the market, country or any other are the portfolio is concentrated on.
To have more money than the amount that was raised by funding to beat the benchmark the fondmanager is orienting on its benchmark. He replicates the above mentioned portfolio by buying Derivatives. Since it is cheaper to buy and hold derivatives and a cash cushion than investing almost all the money in the real shares there is some money left over.
The money left over is the money a so called ALPHA-Manager is able to work with. It is his job to invest this amount of money as advantageous as possible. The correlation between the underlying Portfolio and the ALPHA-investments should be as close to zero as possible.
Due to that constellation it will be way more important to have a very good ALPHA-Manager to earn enough to beat the benchmark after earning all the costs.
Since this was only meant as a short explanation about what portable alpha means, please feel free to add further ideas or recommendations.