Hi all,

136 kHz = 17 * 8 kHz.  Almost anything to do with telephony
has a frame rate of 8 kHz, including T1/E1, ISDN, and xDSL.
The old style carriers used multiples of 4 kHz.

So what you are seeing is not at all surprising.
It would be interesting, for confirmation, if you observed
similar signals at, say, 19 * 8 = 152 kHz (or another
such harmonic where the band is quiet).

73,

Stewart KK7KA

Hello LF group,

>The spread in frequencies and the amount of drift would be >consistent with an assortment of crystal oscillators on the same >nominal frequency - perhaps it is a harmonic of some popular baud >rate or similar?

... I made the observation that whenever I use my ISDN phone line I have a
carrier on 136.000 kHz (I did not check the exact frequency, though).

Best 73

Geri, DK8KW (W1KW)