gas filtering system can be positioned around rf applicator 14 within or outside the bore hole to permit gas recovery through inner passage 42 without water the gas filtering system blocks liquid water and allows only the gas to pass through it other embodiments are within the scope of the claims for example although rf applicator 14 includes dipole antenna 40 other antenna configurations are equally applicable for use with the rf applicator for example referring to fig3 rf applicator 14 can include an antenna 70 which is in the form of an extension of coaxial transmission line 20 the applicators described in conjunction with fig2 and 3 are designed to provide a predetermined impedance characteristic for example to provide a high level of coupling into the coal seam however in other embodiments changing the impedance characteristics of the rf applicator may be desirable for example dielectric characteristic of the subterranean formation may differ or change as the water is converted to steam in such embodiments the applicator may include a tuning mechanism referring to fig4 for example a shorting link antenna 80 is connected to the distal end of coaxial transmission line 20 in essence shorting link antenna 80 is a dipole antenna having a looped end 82 and shorting link 84 positioned across the end an insulated push rod 86 is connected to shorting link 84 such that in operation it can be used to move the shorting link and adjust the electrical length of the antenna a remotely controlled non conducting hydraulic actuator 90 is provided to move push rod 86 in the embodiment shown a center conductor transition 92 is provided between coaxial transmission line 20 and a center.