20. Sketch and describe Roberts latching key and connections.
21. Sketch circuits of bridging station for non-selective party line.
22. How would you arrange the signal code for six stations on a non-selective party line?
23. What is the limit of number of stations on a non-selective party line under ordinary circumstances?
24. State the objections against the party polarity system as shown in Fig. 172.
25. What are the advantages of the harmonic party-line system?
26. To how many frequencies is the harmonic system usually limited?
27. What can you say about the commercial success of the step-by-step method?
28. State the principles of a lock-out party line.