UNID PIP 6420 & 6520 kHz 0110 UTC 1 May 2018

[Traveling Wave]

0110 UTC - PIP was alternating between 6420 and 6520, now steady on 6520 peaking 20db over S9 in WNY. Approximately 1 sec. between signal peaks.
0113 UTC - PIP on 6420 then back to 6520.
0115 UTC - PIPs are alternating again.
0118 UTC - PIP at 6370
0119 UTC - PIP At 6420
0121 UTC - PIP at 6300
0121 UTC - PIP at 6520
0124 UTC - PIP at 6515 peaking at 40db over S9
0130 UTC - PIP at 6510 peaking at 60db over S9
0131 UTC - PIP moved to 6515,6400,6515,6310,6520,6515,6520,6515.
0139 UTC - PIPs have stopped. The PIPs went as low as 6300 to as high as 6520 over this time span. No noticeable pattern in frequency changes, appeared to be random.
0143 UTC - PIPs are back running the same frequencies again in random.
0155 UTC - PIPs still going.
0236 UTC - PIPs still going
0303 UTC - PIPs still going from 6300 to 6520,6525

[digitalmod]

Could it be Over Horizon radar?

[Traveling Wave]

OTH radar is a continuous buzzing type sound, the PIPs are not continuous. I would describe them as a quick pulse that is generated each second, sometimes they pulse on one frequency for a series of seconds before they switch to another frequency. Usually the PIPs cover a series of frequencies and repeat those frequencies over and over.