Walter:
Surely the problem you describe, of interference between HBG and LORAN, was
the result of the (clean) HBG signal on 75kHz getting into the (too-wide)
passband of the airborne LORAN receivers. The solution to that should have
been a better LORAN receiver filter that rejected 75kHz. I imagine that was
the solution at the time.
What we would all like to see is a better LORAN transmit spectrum. It is
very difficult to understand how LORAN is allowed to escape the usually very
strict specifications on unwanted emissions that are applied everywhere else
in the radiocommunication industry. The LORAN transmitter is the last
remaining application of the spark transmitter, in which the antenna is
effectively shock-excited by a fast-rise pulse. Everywhere else in radio the
spark transmitter is kept in it's proper place - a glass case in a museum.
On 100kHz we are told that this is essential modern technology.
It wouldn't be a dificult task to fit them with bandpass filters. The high
power figures shouldn't frighten us into thinking that it can't be done. The
duty cycle of a LORAN transmitter is about 1% so a filter for a 1MW LORAN
transmitter isn't a difficult prospect. The simple answer is that no-one
cares any more about the LF bands. Maybe soon they will just declare that
the radio spectrum stops at 150kHz. Think of the savings that could be made
world-wide - no more need for mains filters on switchmode power supplies!
73
Peter
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