Attenuator

Using an attenuator just after the 1st IF conversion may be more convenient, because it then allows the backend to work at (almost) constant level. Let us assume an attenuation factor $\eta$ (smaller than 1) is used on the chopper. Then

$$Mean\_load / K = \eta * (Trec+T_{load})$$ (21)

and in TREC mode, the sky emission is given by:

$$T_{emi} = \frac{\eta * (Trec+T_{load}) * Mean\_atm}{Mean\_load} - Trec$$ (22)

while with a cold load, Trec is given by

$$Trec = \frac{Mean\_cold * T_{load} - Mean\_load * T_{cold}} {Mean\_load - \eta * Mean\_cold}$$ (23)

T_B is now given by

$$T_B = e^{\tau} \frac{\eta}{B_s}(T_{load}+Trec) \frac{Mean\_sou-Mean\_atm}{Mean\_load}$$ (24)