Receivers for down-conversion of L1 and L2 carrier frequency transmissions from orbiting global positioning system (GPS) satellites

An improved navigation satellite receiver with a super heterodyne receiver channel configured to provide a first local oscillator frequency between L1 and L2 such that the down converted intermediate frequencies of L1 and L2 can be processed by the same intermediate frequency stages and a second mixer stage. A radio frequency (RF) selector switch is provided to select between inputting L1 and L2 to the first mixer. The RF switch is controlled by a digital signal processor (DSP) that also provides automatic gain control (AGC) to an intermediate frequency amplifier. Histories and expected levels of AGC for each of L1 and L2 are maintained by the DSP. The RF switch is briefly toggled over to select one of L1 or L2, while tracking a satellite on the other carrier frequency, just long enough to sample the AGC level needed. If the level is too high, given the histories and expectations for such levels, the sampled carrier frequency is assumed to be jammed, and a high risk for switching over. A switch to the sampled L1 or L2 carrier frequency is therefore prevented, which saves satellite tracking from being temporarily or permanently lost.