FILTERS FOR CA RRIER SYSTEMS 215 



physical resistance. This of course introduces a flat loss but in this case 

 enough gain was available in the circuit to permit it. 



On Fig. 12 is shown a typical transmission characteristic when the filter 

 is operating between 135-ohm resistances. A variety of component parts 

 are required to give this performance. The Alter portion employs mica 

 condensers throughout and a mixture of molybdenum permalloy and air- 

 core retard coils. As many permalloy coils are used as possible in order 



Fig. 13 — Exterior view of the band , elimination filter. 



to obtain high "Q". The air-core coils, of an adjustable type, are used in 

 those arms which control the peak frequencies near the pass band. These 

 arms must be adjusted very accurately for resonance in order to maintain 

 the steep slope of loss in the cut-off region. The equalizer sections employ 

 duolaterally wound air core coils also adjustable in order to set the pass 

 band losses accurately. Mica and paper condensers are used in the equalizer, 

 the latter being used where capacity values make mica condensers extremely 

 expensive. 



