[Lowfer] QRSS Alternative (LONG)

[Lyle Koehler]

More thoughts on modes and bandwidth requirements in the proposed US 137 kHz
band:

The FCC proposal calls for a maximum bandwidth of 100 Hz. That's enough for
real-time CW at 20 WPM, although the keying waveshape will have to be
controlled better than it is in most of today's ham transceivers. PSK31 will
be OK with a properly adjusted transmitter and a linear amplifier. Slower
PSK modes like WOLF (which runs at 10 baud) will be fine, although with the
same qualifications as PSK31. The simple XOR gate BPSK modulator and
non-linear final that I've used in my LowFER transmitter would not be
acceptable on the LF ham band.

Beyond the 100-Hz FCC bandwidth limit, there will be further limits imposed
by "band plans" and by the presence of Loran lines. I haven't followed the
development of band plans for European LF operations, but expect that
similar gentleman's agreements will need to be reached in the US to avoid
conflicts between "broadband" and "narrowband" operation. For really
weak-signal work, it will be necessary to sneak in between the Loran lines,
at least the lines of the Loran transmitter(s) closest to the intended
receiving location. That puts a limit of about 5 Hz on the bandwidth. Maybe
a DSP comb filter will take care of some of the Loran crud at the receiving
end, as long as the transmitter frequency and modulation format are
carefully chosen. Probably the European hams have already come up with some
pretty good solutions, and we will just have to get up to speed on what they
have done. Either that, or re-invent the wheel, and I'm sure there will be
plenty of that :-)

Lyle, K0LR