Mystery "Pips" On 3549.6, 3899.6 and 7049.6 at 0820z

[l0ngwire]

Tonight from 0820z to 0830z I am hearing a "pip" signal on 3549.6, 3899.6 and 7049.6. When listening in the CW mode it sounds like a CW carrier with a bit of modulation. Tonight it is about a half-second beep with about a three second interval.

There was no ID when it stopped.

Signal was about S7 here in central California and about the same strength on the KFS omni SDR up north.

Several hams on the QRZ forum have heard it also in the central US, also around the same time.

Any cluess?

[l0ngwire]

A few weeks later, the mystery signals continue to be heard here in central California.  I've observed it as strong as S8 and on for as long as 40 minutes. I've heard them several times between 0700z and 0900z. The frequencies have shifted slightly higher and are on 3550, 3900 and 7050 simultaneously.

There is a thread on QRZ.COM about them. The 40 and 75/80m signals appear to be even stronger in the eastern US.  One member has heard the same signal on 14050, but thus far I've not heard it there.  The same poster got some detailed photos of the 14050 signal on a SDR. (https://forums.qrz.com/index.php?threads/whats-that-beeping-on-7-047-and-3-547.856555/page-3)

(From QRZ posting of beep seen on 14050) "The bright trace to the left is foreign broadcast, just above the band edge. Note that at the bottom there are two strings of pulses close together, this double pulses occurs every 9 single pulses."


(From QRZ posting of beep seen on 14050) "Here is is with the waterfall sped up to max. Each burst looks like a group of pulses:
The span of these bursts is about 300 kHz. The bursts are about 2.5 - 3 seconds apart."


From a California SDR of 3550 signal: