CHOKES AND TRANSFORMERS 



gives the required air gap, d, as a proportion of the total length of the magnetic 

 circuit, /. By dropping down from this point to the horizontal axis one then 

 reads off a value of NIjl, where A'^ is the number of turns required and / is 

 the length of the magnetic circuit in cm. As / and / are known, N can be 

 worked out. From the known minimum frequency and maximum primary 

 voltage to be employed, the value of -6max may be calculated. The Hanna 

 design curve given is satisfactory provided 5max does not come out to more 

 than 1,000 gauss. If jBmax works out very different from 1,000 gauss, try 

 another core. 



Having found a core, gap and number of turns which gives the required 

 inductance at the anticipated polarizing current, the rest of the design pro- 

 cedure — calculation of the winding resistances — is the same as for unpolarized 

 chokes and transformers, except that in the case of transformers it is probably 

 best to allot rather more window area to the primary than to the secondary 

 winding. 



REFERENCES 



^ Amateur Radio Handbook Amateur Radio Relay League 



^ Macfadyen, R. a. Small Transformers and Inductors London ; Chapman and 



Hall 

 3 Hanna, C. R. /. Amer. Inst, elect. Engrs. 46 (1927) 128 



314 



