5MHz signals go 'fuzzy' at night?

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5MHz signals go 'fuzzy' at night?

Hi All,

Ive only just moved onto 5MHz WSPR, and noticed an oddity that so far I cant explain,

Last night, after an afternoon of very nice, clean decodes, I noticed that after about 19:00, when it was dark, I stopped being able to decode, even though there were signals at good strength on the waterfall. But, these signals were no longer nice clean lines, but had become broad, fuzzy patches on the waterfall, 30-40Hz or more wide! All signals on 5MHz showed this, but switching to 40m or 30m for example showed nice clean lines and decodes again, this only happened on 5MHz?

Has anyone noticed this before? Is it some odd propagation effect, or some form of local interference effect? A listen around didnt reveal any unusual transmissions, at least nothing I could hear! Just a bit of WSPR, some MFSK type thing and a bit of SSB

As I said, only seemed to affect 5MHz, anyone any ideas?

Martin G7MRV