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From Cesare I5TGC:
> The
Signal you receive is like a telephon call, some old systems use a 25 Hz a.c.
> with one second duration and 4 seconds space. Nevertheless it is very
difficult
> that these signals can reach your receiver.
Not difficult to hear if someone has a PABX not
far from the ELF antenna- and the bigger the antenna then probably the further
away it can be.
I can hear the ringing from my own PABX (with a
similar mark/space ratio to that described) from ELF all the way up through most
of the HF range on a variety of antennas and receivers.
73
Dave
ZL3FJ
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