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Dear MF users,
please make sure to avoid placing
a carrier or beacon very close to the carrier of an NDB. This could
severely irritate the direction finder, without the pilot even noticing that
interference is present.
For example, consider an amateur
sending a long QRSS carrier 0.1 Hz beside the NDB carrier. Even if he
was 20 dB (!) weaker than the NDB, the superposition
of magnetic fields would periodically swing the DF needle by up
to +- 0.1 rad (5.7 degrees) around the correct azimuth position,
once every 10 seconds. Even with low power, such a situation
cannot be ruled out completely.
During the discussions with the
German flight safety authority preceeding the MF allocation, we have briefly
considered this "coherent interference" scenario. We assumed that any
amateur would carefully monitor the frequency before commencing a transmission,
and stay away at least several Hz from any audible NDB carrier.
Best 73,
Markus (DF6NM)
From: [email protected]
Date: Fri, 5 Oct 2012 16:20:10
-0400
To: [email protected]
Subject: LF: Re: 630m Band
Plan
...
- “good idea to have
narrow guard bands around existing aeronautical beacons”: it is trivial, that
other regions in the world will probably need different such guards. Just to
clarify: a pilot will tune to the frequ (in kHz, no fractions) of a NDB and
expects that the relevant Instrument will show him the direction to that NDB
relative to his AC. He will listen to the ID just to make sure. Hopefully e.g. a
QRSS Station on top will not disturb the instrument? Most probably our power
restrictions will show that this safeguard unnecessary; we introduced it as an
additional good will act. NDBs are a dying species.
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