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BELL SYSTEM TECUXICAL JOURNAL 



as mechanical termination for the lead wires and also as connection to larger 

 size spring wires forming the rest of the shock-proof m.ounting. 



Another type of wire support that has found considerable practical use 

 and is superior to the straight lead and solder cone type of connection is that 

 of the headed wire. This is shown in Fig. 8.6. A headed wire is similar 

 to that of common pin and may be connected to the crystal by sweating the 

 head to the crystal as shown. This has certain advantages over the solder 

 cone in that the head of the wire being a machined part is always constant 

 and the distance d, as shown in Fig. 8.6, is the same for all mountings. The 

 amount of solder necessary to sweat the head to the crystal is considerably 

 less than in the case of the cone and hence this type of mounting will have 

 less dissipation at the higher tem.peratures. One other factor not men- 

 tioned above is that the coupling between the vibrating system of the wire 

 and the vibrating system of the cr3Stal is considerably reduced by the use of 



^1 



^ 



Fig. 8.6 — Headed wire t^-pe mounting. 



the headed wire. This is an important factor in reducing what may be 

 termed a double system of standing waves on the wire. One standing wave 

 system would result from reflections from the clamped end of the wire, while 

 the other would result from reflections between the clamped wires coupled 

 through the crystal. This may be reduced by a reduction of coupling be- 

 tween the crystal and wire vibrating systems. 



Measurements have been made^ on the efi"ect of clamping the wire-sup- 

 ported crystal at various points, on the activity and frequency of several 

 different crystals used in oscillators and filters. Figure 8.7 shows the efi"ect 

 of clamping a 500-kc CT type crystal such as now used in the FT-241 holder. 

 Figure 8.8 shows the same condition for a 370-kc CT crystal. It will be 

 noted that in these two cases with the decrease in frequency of the cr>'stal 

 that the coupling between the wire and crystal has decreased, as shown by 

 a smaller change in frequency and also, that for the lower frequency crystal 

 the change in activity is modified only when the clam.p is very close to a loop 

 of motion on the wire. The mountings of these crystals were of the type 



