On Sat, 26 Feb 2005 10:29:29 -0500, "xpyttl"
wrote:

It did surprise me to see this on 80, though. As Roy points out, the
absence of atmospheric noise is not a valid assumption on HF, and noise does
increase with decreasing frequency.

However, the noise power is proportional to bandwidth, so if the
throughput rate is not defined, slow down the bit rate to reduce the
required receiver bandwidth, until the noise is weaker than the
signal. While the lower HF noise is not pure white noise, this
principle can still be applied.

For instance on the 135 kHz LF band, it is quite common to use QRSS
with a dot time of several seconds or even a minute and the reception
is done visually on the "Waterfall" (spectrogram) display. Although
the LF transmitter power might be several hundred watts, the
transmitter antenna efficiency is usually much worse than -30 dB, so
the radiated power is well below 1 Werp and the noise level is much
higher than on HF.

Paul OH3LWR