Top Up TV CAMs

I'm reading the spiel coming out of TUTV and also the discussions at DS regarding CAMs for TUTV cards. My problem is this: why are they not suitable for all STBs?

My logical reasoning is this: as the TV signal goes into a STB, surely a de-encryption can take place between the aerial and the STB?

TV signal goes into CAM, CAM goes into STB, STB goes to TV. Surely this would work?

Or am I just being stupid? I have a Panasonic TUCT20 btw

Not saying you are stupid... but it isn't this simple.

The CAM sits quite a long way down the reception path - quite a long way after the tuner, the demodulator and effectively it sits just a bit before the MPEG2 decoder.

For this reason many DVB receivers have a CI slot (common interface) that allows a CAM (conditional access module) to enter the chain - and this is what TUTV CAMs connect to.

To do what you suggest would be really expensive - the CAM would need to have a full DTT receiver, CAM AND modulator in it. It would also need to do all the muxes at the same time - or tune between them with a second remote control. Neither of these are cheap or likely.