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Electronics Paper 2, May/June 2009  
Questions: 1 2 3 4 5, 6 &7 8 9 10 Main
General Comments

Question 4
(a) Draw and label a block diagram of a tuned radio frequency receiver (TRF).

(b) State:

(i) two disadvantages of TRF over a superhetrodyne receiver;

(ii)four advantages of superhetrodyne receiver over TRF.


The expected answers were:

(a) A block diagram description of the tuned radio frequency receiver (TRF) is displayed below:

(b)(i)    Disadvantages of the TRF over the SUPERHET receiver include:      
-           The need to have all RF stages track one another
-           Instability due to large number of RF stages.
-           Received bandwidth increases with frequency (varies with centre
-           Gain is non-uniform over a wide range of frequencies.

 (ii)       Advantages of the superhet receiver include
-           IF stage permits use at very high frequencies.
-           Because many components operate at the fixed IF, they can be  optimized.
-           Less expensive.
-           Better selectivity
-           Improved circuit stability.
-           Uniform gain over a wide range of frequencies.

This question was on communication systems.  Candidates did not do well in this question which had in the last couple of years been featuring on either the TRF or the SUPERHET.  This could be adduced to ill-preparation culminating in confusing the TRF with the SUPERHET.

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