Losing tones

I've noticed 410-477 tones are not used (with little exception eg. at one synchronization 410 tone is used, sometimes is not used). What is the probable cause? I've heard amateur radio can cause this, however as far as I know nobody broadcast radio in my area.

Following there is my SNR on particular tones graph.
http://imageshack.com/a/img706/750/n412.png
Following there is my Hlog:
http://imageshack.com/a/img835/7722/61u3.png
Following there is my QLN:
http://imageshack.com/a/img854/3830/l1lt.png

I've noticed for example that the QLN is very similar at the end used tones as at the not used tones. For example both tone 415 and 500 have QLN -145, however tone 415 is not used, but on tone 500 there is SNR 30.25 and 7 bits. It is very curious.

Following there are my current line stats:
http://imageshack.com/a/img824/2434/2ocl.png

This connection is from 38 days and SNR margin 3.3-4.1 dB (rarely 4.8 dB).

Best regards
konrado5

Edited by konrado5 (Sat 22-Feb-14 23:21:20)

More likely to be commercial AM or LW stations too, and these can be many miles away and still affect you, and worse at night

An AM radio tuned to the notched area might reveal the culprit

In reply to a post by MrSaffron:

More likely to be commercial AM or LW stations too, and these can be many miles away and still affect you, and worse at night

An AM radio tuned to the notched area might reveal the culprit

Unfortunatley on my AM radio I have frequency to 1600 Khz. By contrast, 410 tone is about 1800 Khz. Moreover, I've noticed SNR nearly not used tones is the most stable. What about my Hlog and QLN?

Best regards
konrado5