Limitations of Hydrogen Maser Frequency Standards Due to Receiver Noise

In this paper we give a description of the different noise sources occurring in the receiving electronics of an active hydrogen maser and their influence on overall stability. It is shown that the most significant noise sources in the PLL locking a VCXO to an atomic oscillator are the preamplifier and the frequency multiplier. A measuring method yielding the noise behavior of the entire receiver is presented and compared to the calculated result obtained by taking into account the different relevant singular noise sources in the loop.