In early 1943 consideration was given to following the lead
set by the USA military in adopting FM transmissions for it's HF field
radios. Early tests showed promise so it was decided to modify three
ZC1 Mk-1 sets for FM working so that direct comparisons could be made
between FM and AM transmissions, using as near as
possible identical sets, under
the same operating conditions. The tests proved conclusively that FM
was superior under difficult atmospheric conditions.
Britain was also developing the experimental Wireless Set
No. X32 series of sets to evaluate the use of FM in HF radio sets and
information and ideas were exchanged.
However neither Britain or New Zealand decided to introduce FM Field radios
at that time despite the success of the tests. This appears to have
been mainly related to the cost of retooling for production, the higher cost
of the sets, logistical problems in spare parts, test equipment and
retraining of signals and technical service staff.