[Lowfer] 518 kHz Navtex interference

[Garry]

On June 9 William Hepburn reported interference to Navtex signals on 518 
kHz by station CHLO broadcasting HD radio on 530 kHz from near Toronto, 
Canada (see https://www.dxinfocentre.com/navtex.htm and 
https://www.lwca.net/mb/msg/11452.htm). Interference is present here in 
faraway Chicago and severely limits Navtex decoding. Mariners throughout 
the Great Lakes must be similarly impacted. At first I thought this was 
from some other source but the in-band on-channel digital sideband 
spectrum for HD radio matches what is seen and the conventional radio 
signal at 530 kHz consists of ethnic talk and music as expected from 
CHLO. In addition to the flat digital spectrum that blankets 518 kHz 
there seems to be a narrow subcarrier, perhaps to carry other content.
-- 
73, Garry, K3SIW, EN52ta, Elgin, IL
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