[Boatanchors] EF Johnson Filter

[John Franke]

The Johnson 250-20 low pass filter consists of four individually 
shielded sections, capable of handling more than 1000 Watts RF, 
amplitude modulated.  Cut-off frequency is 45 MHz with "M" derived 
end sections adjusted to provide maximum attenuation at 57 MHz, the 
center of TV channel 2.  Attenuation of harmonic and spurious 
frequencies above 54 MHz is 75 dB or more.  Insertion loss less than 
0.25 dB.  Characteristic impedance of the filter is 52 Ohms. 
Construction permits the replacement of Teflon dielectric of the 
fixed capacitors should there be damage due to accidental overloads. 
Standard SO-239 coaxial connectors are used for input and output 
terminals.  Amateur net....$16.50 (1953)