Global Navigation Satellite Systems (GNSSs) are vulnerable to several threats including jamming and spoofing. Jamming is the deliberate transmission of powerful Radio-Frequency (RF) signals which can easily overpower the much weaker GNSS components disturbing and, in some cases, denying GNSS operations. In recent years an increasing number of cheap, though illegal, jammers have become commercially available. In this paper, the impact of these jammers on Global Positioning System (GPS) and Galileo L1/E1 signal reception is investigated. It is shown that the signals of each system are affected in similar ways and this is due to the wide-band nature of the jamming signals. Narrow-band receivers are less impacted by jamming since they are able to filter out a greater portion of the interfering signal. Interestingly, the presence of a pure pilot channel in the Galileo E1 modulation allows receivers to use a pure Phase Lock Loop (PLL) which in turn allows signal reception in the presence of stronger jamming signals with respect to the GPS L1 C/A case.