Please enable JavaScript.
Coggle requires JavaScript to display documents.
Lecture 13- Dicke switch (Passage through the varying atmosphere (In…
Lecture 13- Dicke switch
Dicke switch receiver
if dG fluctuations were very slow (minutes) you could calibrate the entire system by repeatedly pointing the antenna a a reference point of known brightness more frequently than this.
However this is never the case for receiver "1/f noise" (fluctuations to fast) have to adopt a different strategy by building the reference system into the receiver itself
-
On short enough timescales the gain variations in the receiver are small (like fast shutter speed) this is to compare the output of the receiver against a constant power source (a load resistor at a fixed temperature) on short timescales
fast switching of the receiver input between the antenna and the resistor load and averaging the difference bwteen them.
-
-
Advantages
-
-
if Tload-TA =0 there is a perfect balance between antenna temp ad load temp the receiver is perfectly insensitive to gain variations on timescales longer than tswitch and the output changes only if TA changes to alter the balance very important to equalise Tload and TA as close as possible
Disadvantage
-
because antenna is connected to the target and load for only half time hence TA data channel has higher noise, tload data stream has the same noise as TA channel
-
-
Varients
Double Dicke
RF switch switch position 1: receiver 1 connected to antenna, receiver 2 connected to load
-
-
Since one receiver is always looking at the target source one factor of root 2 from the single dick is gained back
-
-
-