Jerry W. Jenson proposes an explanation of the Pioneer 10 observations
with his and Jacques Moret-Bailly's CREIL (Coherent Raman Effects on
Incoherent Light) theory:

Propagation of electromagnetic waves in space plasma
Jerry Jensen, Jacques Moret-Bailly 2004 Jan 25
http://arxiv.org/abs/astro-ph/0401529

Supernovae Light Curves: An Argument for a New Distance Modulus
Jerry W. Jensen 2004 Apr 9
http://arxiv.org/abs/astro-ph/0404207

and in a discussion forum:

http://www.badastronomy.com/phpBB/viewtopic.php?t=14433

My rough understanding of the CREIL mechanism is that it involves
light (or any electromagnetic radiation) travelling through plasma or
atomic/molecular gas and being both attenuated and redshifted or
blueshifted, according to the other electromagnetic radiation which is
incident on the plasma or gas, and according to other factors such as
density, pressure etc.

I am not arguing for or against this or other theories about the
Pioneer 10 observations. I will write to Jerry Jenson, referring him
to this discussion, and ask him what his theory predicts about the
Cassini observations.

- Robin http://astroneu.com