'Diffuse' threshold decodable rate 1/2 convolutional codes

This paper shows the existence (by construction) of rate
\frac{1}{2}
convolutional codes that correct bursts of length
B
or
t
random errors. The codes have memory length and guard space requirements that are asymptotically
4B
and minimal effective length. Kohlenberg introduced the term "diffuse code" for his two random-error or single-burst error-correcting codes with minimal effective length and both a memory and guard-space requirement of
3B + 1
. To this point, there does not seem to be any procedure for finding codes with minimal effective length and guard space requirements asymptotically
3B
.