To help solve the 41 meter (7300-7500 kHz) shortwave transmitter overload a quarter wave stub has been inserted to help attenuate just that part of the band. More info here.
The filter is wide so there is affects frequencies +/- 10% of the design frequency. The further away from the design frequency, the less the attenuation.
The filter has improved the overload issue and is only a minor inconvenience on the 40 meter ham band.
