  Variable-length feedback codes can provide advantages over fixed-length
feedback or non-feedback codes. This letter focuses on uncoded
variable-symbol-length feedback communication and analyzes the autocorrelation
and spectrum of the signal. We provide a mathematical expression for the
autocorrelation that can be evaluated numerically. We then numerically evaluate
the autocorrelation and spectrum for the variable-symbol-length signal in a
feedback-based communication system that attains a target reliability for every
symbol by adapting the symbol length to the noise realization. The analysis and
numerical results show that the spectrum changes with SNR when the average
symbol length is fixed, and approaches the fixed-length scheme at high SNR.
