[Elecraft] K3 birdies - question?

Wed Mar 4 12:28:17 EST 2009

James
When you start looking around for sources of these external
signals, be prepared for some surprises.  I had a fairly
strong signal on 10m that was a real nuisance.  I turned
off the power to my house and it went away.  I finally
found it in the controller for our air mattress in the
bedroom.  Now, during a serious 10m effort, like the
ARRL 10m contest, I just unplug the controller until after
the contest.
73, Bob N6WG

----- Original Message ----- 
From: "KC2UEE" <KC2UEE at gmail.com>
To: "Richard Ferch" <ve3iay at storm.ca>
Cc: <elecraft at mailman.qth.net>
Sent: Wednesday, March 04, 2009 8:15 AM
Subject: Re: [Elecraft] K3 birdies - question?

> 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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