From the FCC's PRM on LF

[Andre Kesteloot]

25. We propose to require that amateur stations in the 135.7-137.8 kHz
band meet the technical limits suggested by Canada in the WRC-03
preparatory process, noted above.   As provided in the Canadian
proposal, we believe that sharing of this spectrum would be facilitated
if the amateur station is limited to an EIRP of 1 W and the transmission
bandwidth is limited to 100 Hz.  Because of possible difficulty in
measuring the EIRP of the amateur station in this frequency range, as
noted by ComEd, we additionally propose to limit amateur output power in
this band to 100 W PEP.  We seek comment on whether these limits on EIRP
and PEP are appropriate. We propose no restrictions on antenna size or
design for amateur stations because such restrictions would inhibit
experimentation, and we believe that interference to other users can be
adequately addressed by the proposed power limitations.  We also propose
to limit access to this band to amateur operators holding a General,
Advanced, or Amateur Extra Class license, as requested by ARRL, as a way
to insure amateur operations would be conducted in a manner that
minimizes the interference potential to other users.  We note that with
an allocation of only 2.1 kilohertz of spectrum in this band, amateur
radio operations may be limited to propagation experiments, telegraphy
and low speed data applications. Nonetheless, this allocation would
benefit amateur experimentation of the LF range.  We seek comment on all
of these proposals for a secondary amateur service allocation in the
135.7-137.8 kHz.