recording one channel and watching another with single tuner box

[moscam]

i have a technosat hdva decoder with an external hdd, whilst it has only one tuner i am told i can record one channel and watch another if they are both on the same transponder
can anyone tell me how to go about this because up to now i have been singularly unsuccesfull, each time i try i simply get a message saying i cannot record one channel and watch another

[Shady]

Astra 1N / Astra 2A / Astra 2B / Astra 2D / Eutelsat 28A (28.2E) - All transmissions - frequencies - KingOfSat
see that list? thats the channels on 28.2e (sly uk).
they're all split up into transponders with so many channels per transponder.
for instance if you are recording channel 4 , then you should be able to change channel to film4