[Elecraft] K3 birdies - question?

[Richard Ferch]

James,

Any signal coming in from the antenna will change pitch when you tune the
radio in CW, SSB or DATA mode. That's not how you tell a birdie from a real
signal - it's removing the antenna that distinguishes them. A real signal
will either disappear entirely or at least become much weaker when the
antenna is removed. Internal birdies, on the other hand, usually sound
louder when the antenna is removed, because the noise floor surrounding them
drops.

Note also that there is a difference between the situation with nothing
connected to any of the K3's antenna connectors, and having anything at all,
such as an antenna switch or a dummy load or just a short piece of coax,
connected to one of the connectors. If the signal is still there with
nothing whatsoever touching any of the antenna connectors, then it is likely
a birdie internal to the radio. From your description, it sounds as if you
are hearing external signals, not birdies.

There are different kinds of birdies. Some are on fixed frequencies, just
like real signals, and others are harmonics that tune more rapidly than real
signals. The birdies that are removed by the new signal removal feature are
the ones that change pitch abnormally rapidly as you tune the radio.

With a real signal, if you change the receiver's frequency by 10 Hz, the
pitch of the signal changes by 10 Hz. With one of these "fast" birdies,
changing the tuning of the radio by 10 Hz might cause the pitch of the
birdie to change by 300 Hz. These "fast" birdies also change pitch when you
rotate the Shift control - real signals do not.

Using a 2.7 kHz roofing filter, as you tune past a real signal it will be
audible over a tuning range of about 2.7 kHz, and will sweep steadily from
very low to very high pitch (or vice versa) as you tune past it. In
contrast, a "fast" birdie might only be audible over a tuning range of about
100 Hz, i.e. as you tune the radio past the birdie it will jump right across
the audible range of pitches within only 100 Hz of dial movement. These are
the birdies that the signal removal feature works on. It doesn't work on
birdies that are on fixed frequencies and tune like real signals.

73,
Rich VE3KI