02 October 2008
I've been working on a couple of projects over the last
few days. One of them is collecting signal strength data using the HP 3586B
The plot below shows five days data for two stations, WWVB
at 60 KHz and NML4 at 25.2 KHz.
WWVB is a standard time and frequency station operated by
the National Institute of Standards and Technology from a site in northern
Colorado. It operates with an ERP of 50 kw.
NML4, operated by the US Navy from LaMoure, North Dakota,
is part of the Navy's worldwide submarine communications system. It operates
with an ERP of 500 kw.
There's quite a difference in propagation modes shown in
the two signals. NML4 is relatively stable, with a day/night difference of a
couple dB, and the sunrise/sunset dips are at most 4 to 5 dB. WWVB, in
contrast, shows nearly 10 dB day/night signal difference and sharp, deep
Although only 35 KHz apart in frequency, it's more useful
to look at the ratio of frequencies; WWVB operates at a frequency more than
twice that of NML4. This difference is enough to cause different propagation
mechanisms. I hope to address this subject in more detail after collecting