The 2200 m band is only 2.1 kHz wide: 135.7 kHz to 137.8 kHz and is allocated to amateurs on a secondary user basis. In such a tight band, the only sensible modes of operation are CW (morse code) and other low bandwidth modes such as QRSS (extremely slow CW), DFCW (Dual Frequency CW) and Castle mode, a new mode invented by ZL1BPU. Because of the nature of slow data rates, an extremely stable frequency is needed at both ends.
As one might expect there are many challenges associated with LF. There is almost no commercial equipment that covers this band. The majority of amateurs will build their own transmitter and in some cases the test equipment required to test the performance of their equipment (such as RF Ammeters). Most HF receivers and tranceivers exhibt inferrior performance on 136 kHz. Preamplifiers and preselectors may need to be built to improve performance. Probably the biggest problem to the average amateur will be building an antenna for transmitting on 136 kHz. Most designs that will fit in the average backyard have efficiencies in the order of a tiny fraction of 1%. Elaborate inductors are needed to tune such electrically tiny antennas to LF. The voltage on the hot end of the inductor is expected to reach many kV, even with low to moderate power. The low antenna efficiency makes the use of big amplifiers (hundreds of W) almost compulsory, and reaching the allowed 1 W EIRP (Effective Isotropically Radiated Power) is mostly a pipe dream for the majority.
Overall, experimenting in LF is not as hopeless as perhaps is depicted in the previous paragraph. The MOSFETs that are commonly used in LF amplifiers are cheap and readily available. Even the lowest spec'd oscilloscope will be useful in LF. Super stable frequency can be generated with common crystals with an appropriate frequency divider circuit. DDS is also a good option for LF. The most experienced users of the band are quite happy to assist newcomers to get started and there is plenty of documentation, both online articles and books, that can be used as reference.
A simple 137 kHz MEPT for the beginner LF enthusiast
*NEW* Design from scratch a class-E PA for 137 kHz.
Earth conductance experiments on 136 kHz
The new variometer
Old transmitter notes
Partial log book
ISDR-136-KIT and BPF-136-KIT
VK1SV LF/MF grabber
Low Frequency experimenter's mailing list on Yahoo This mailing list is used by 136 kHz and 472 kHz enthusiasts in Australia and New Zealand to discuss all things LF/MF, schedule QSOs and advertise any other activity on LF.
DX Summit cluster spots fro 136 kHz (and 500 kHz sometimes)
A typical day on LF (well, kind of!)