I'm listening on 13560.09 khz right now (USB) and I am hearing about 2 different beeps from 2 different stations, the timing is different for both but the 2 second beeps is strongest.
hold that thought... at one point they were in sync but now they are independent...
Kinda sorta sounds like the old video game pong but I digress ;-)
73 Vince
ka1iic