have you scanned for channels in the box menu?
if you have a good external aerial, and ideally one straight run of good quality twin screened RG6 cable from it to the receiver, then there should be no problem A good installer will check the installation with field strength meters. call him back if in doubt.
. Many amps just amplify noise and do more harm than good, so do not waste your time with such 'patches'. Get the aerial or the box right and everything else will follow.....