baseband channel 500 comprises a dac 505 a digitally controlled oscillator dco 510 an active filtering and amplifying component 520 shown as a dotted block containing filtering and or amplifying elements a passive filter component 530 and feedback loops 570 575 580 585 590 595 in fig5 the passive filter component 530 comprises a plurality of resistance elements that are configurable to receive the output from the active filtering and amplifying component 520 by means of switch elements although only three rows of resistance elements and their associated switch elements are shown for each of the lines forming the output of the active filtering and amplifying component 520 it will be appreciated that any number of rows of resistance elements and their associated switch elements can be provided in accordance with the particular application here each row of resistance elements and their associated switch elements corresponds to a particular frequency band as shown for the negative line output from the active filtering and amplifying component 520 there is a resistance element 532 associated with a switch element 534 a pair of resistance elements 536 538 connected in series associated with a switch element 540 and three resistance elements 542 544 546 connected in series associated with a switch element.