ELECTRICAL WAVE FILTERS 



413 



(2's of the best electrical condensers may be as high as 10,000, which 

 is of the same order as the crystal Q, and hence such elements can be 

 employed advantageously with crystals. It is the purpose of this 

 section to discuss the possibilities and limitations of filter sections em- 

 ploying crystals and condensers only. 



The simplest types of filter sections are the ladder type networks 

 illustrated by Fig. 6. If crystals and condensers only are employed in 



U/^ 2C| 1-1^201 



ELECTRICAL 



STRUCTURE 



A 



X2 ' "/Z^'-\ 



2C2 



2C2 



2C2 =L 2C2 



1 C4 



g 



Ll^ 2C| 1-1/2 2C| 



2C2l-3g Xc4 2C2 



^U 



PHYSICAL 

 STRUCTURE 



Ca =i=C4 Ca 



2C2 



2C2 



3r 



I — I -*— f 



QSIZD 4=c 



^ 



31 



REACTANCE 



CURVES FOR 



EACH ARM 



ATTENUATION 



CHARACTERISTIC 



D 



FREQUENCY 



FREQUENCY 



FREQUENCY 



MID SERIES 

 ITERATIVE 

 IMPEDANCE 



E 



• |FRE 



_^^ Iquency] 



y h If*"/-" °° 



A 



FREQUENCY 



yfl % ,-^ 



-R^. 



■FREQUENCY 



fl/ f2 f0O2|,^' 



MID SHUNT 

 ITERATIVE 

 IMPEDANCE 



A 



y¥y 



FREQUENCY 



i.ool' f2 / 



/U 



I FREQUENCY 



' fl / 



hJ\ 



fooi/| 1 FREQUENCY 



fl f2l ,' 



Fig. 6 — Ladder networks employing crystals and condensers. 



this type network, there are only three types of single band sections 

 possible, all being band-pass filters. Figure 6 shows these sections, the 

 impedance characteristic of each arm, the attenuation characteristics 

 of these networks considered as filters, and their iterative impedances. 



