[Elecraft] K3 birdies - question?

[KC2UEE]

Rich,

Many thanks for your reply.

>From your description, it then sounds as if I'm hearing a real signal.  I do
have a theory that there may be some sort of electronic signal getting into
my feedline.  My coax isn't routed ideally, as a good portion of it runs
between two entertainment centers chock full of transformers, etc.

These birdies or signals as I hear them change in pitch over a wide range,
not just 100Hz.  For example, if I start at 28.375, I can hear a solid
tone.  As I go to 28.376, the tone pitch increases and so on until it peaks
at 28.380.  At 28.381, I can no longer hear it.  If I go back down in
frequency, the pattern repeats itself with the tone pitch decreasing.

I seem to hear these "birdies" spaced every 500-700 KHz.  I'm going by
memory now as I don't have the rig in front of me.

If I remove the antenna, most of them go away.  When I say most, I'd guess
about 98% of them.  Only some which are very strong are still barely
audible, but their behavior doesn't change as I tune around.  They are not
by your description fast tuning.

With the antenna connected, the loudest of these signals will peak my
S-meter at S3.  With no antenna, it may be an S0-S1.

Interestingly, removing the antenna does not affect the sub receiver as I
can still hear them a little bit when the sub is set to ANT1.  Switching the
sub to the BNC though, and all remaining signals disappear.

I'll have to play around a little bit more to determine the origin, but I
was surprised to suddenly hear all of these signals spaced quite evenly
apart.  I began to think that this was synthesizer noise, as it does sound
similar to the DDS signals.  I remember telling Wayne over the phone that I
was pleasantly surprised after the build, because the first thing I did was
to tune around the entire frequency range with no antenna attached to test
for birdies, and I did not hear any at all.

73,
James KC2UEE




On Wed, Mar 4, 2009 at 10:07 AM, Richard Ferch <ve3iay at storm.ca> wrote:

> 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
>
>
>
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