[Lowfer] UNID on 138005 KHz

[Andy - KU4XR]

Hi all:

For anyone interested.. I monitored 136 KHz WSPR overnight, and during the 1 pm hour ( local time ) , I was
hearing " tones " .. I didn't pay attention at first, but it was repeating, and that got my attention.. I began raising 
the frequency on the radio to bring the tone down, and found the frequency to be 138005 KHz .. The UNID sounds
like it is sending a , not so perfect - " T N " .. I recorded the audio with SpecLab, and used Audacity to look at
the audio plot.. After looking, and listening a few times, the signal seems to be 2 different transmitters..
1 sending a single tone - the " T " , and 2.5 seconds later, the 2nd replies with the " N " .. The " T " is slightly 
louder than the " N " and that is what has me thinking it is 2 transmitters .. It is also possible that the " N " is
being sent at a slightly reduced power level, and the 2 tones, at different power levels make up a signalling
modulation of some sort .. just conjecture on my part, this is the first time I have ever heard it.. The signal stopped
at 1:57 pm local time and has not returned as of 3pm.. I have dropbox links to the SpecLab captures, and 
audio .. ( 4-1/2 minutes ) .. I am curious as to what I was hearing .. BTW, the receiver bandwidth was at 2.4 KHz
so the signal is relatively strong.. Thanks for any comments:

Link to the capture folder .. contains 4 captures:

https://www.dropbox.com/sh/5yhdkl7wdncmklt/AAD2ADAKvAFuA3lpQSWtl_a3a?dl=0

Link to the audio file:

https://dl.dropboxusercontent.com/u/49203948/UNID%20on%20138005%20KHz.mp3

73: Andy - XR