up conversion problem in Simulink

Hi,

I want to up convert a signal with the following structure: The source and a "Sine Wave" block are connected with a "Product" block. Theoretically the up converted frequency is determined by Sine Wave -> Frequency, but actually something strange happens.

By using following parameters:

_Sine Wave block: Frequency = 1000000 Sample time = 1/4000000

Product: Sample time = -1 _ the up converted frequency is about 800 MHz.

By using following parameters:

_Sine Wave block: Frequency = 10000000 Sample time = 1/40000000

Product: Sample time = -1 _ an error occurs: Cannot determine a sample time for block Product.

Who can help me with this problem?

Thanks Owen