LF: Strange signals on 25 Hz (!) - any info ?

[DL4YHF@aol.com]

Hello Group,

Has anyone of this group ever heard about signals in the range of 25 Hz, like this:

- a few pulses of about one second length each, about 4 seconds pause between them
- transmitted irregularly, sometimes not present for days or weeks
- obviously NOT related to the mains line, no harmonics or images at 50 and 75 Hz etc
- seem NOT to travel through the mains line.

The following is quoted from Renato Romero:

>>>Hi Wolf,
about that strange signal at 25 Hz: I receive that signal since 1997, when I started with regular reception below 50Hz thanks a circuit of IK1ODO with OP07 op amplifier and a big T marconi antenna. Those strange dots appear sometimes, not always at the same time, and not always in the same form: sometimes there are one o two dots, sometimes there are 13 dots or more. They disappear for many days, then appear again with a not regular schedule.
About the origin: agree with you about the not natural origin, is clear; but what they really are ... it's a mystery.
They are not inducted by main power lines because they are not present in the reception with a big horizontal loop (30m x 30m, 3 turns), instead of the signals on the electric line at 1024Hz, present on air and very strong in horizontal polarization.
They are not caused by not linear loads on the electric line: that signals appear like a mirror with 50Hz (and 150Hz, 250Hz...): in this case there is no signal at 75 Hz. 
<<<

Any ideas ? Another submarine "wakeup" transmitter ?

73, Wolf



P.S. Looking forward to Dick's Feldhell transmission. Will try to answer in that mode, but I few its not really suited for my low-power signal - so possibly will reply in CW.


P.P.S. Walter DJ2LF will hold his LF talk at the Ham Radio fair in Friedrichshaven on Friday June 28, after 16:00 local in hall 2, room "C", after an introduction by DL1VDL. .... at least, this is written in the german CQ DL magazine. They warn about "problems with the parking space" this year and ask visitors to use the shuttle bus. Hope to meet you there !