[Elecraft] K3 Birdies

[John Lemay]

Dave

 

I think you've been very unfortunate that that many birdies. I have found 4
within the 20m band on my K3, which is a 10w kit version, no second
receiver.

 

I found nothing on 14.186.6.

 

All those birdies are completely masked by site noise as soon as the aerial
is plugged in.

 

Regards

 

John G4ZTR

 

  _____  

From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of David Gilbert
Sent: 10 February 2009 07:48
To: elecraft at mailman.qth.net
Subject: [Elecraft] K3 Birdies

 


I recently completed K3 #2623 and everything went very smoothly, except that
I'm really surprised at all the birdies I can hear on the main receiver with
the antenna input simply looking into a precision dummy load (or open
circuit ... no difference either way).  20m is clearly the worst, with over
50 discernible birdies ranging from barely readable to S4 on the meter.  The
majority are S0 and S1, but I had three each on 20m and 40m that were S2 or
louder.   They are definitely synthesizer artifacts since their pitch jumps
in large steps as I tune across them.  

All of this is in the main receiver ... I can find only a very few really
weak birdies in the subreceiver.    I didn't rigorously check all of the
bands, but 15m and 10m are virtually clean, even on the main receiver, and
80m and 40m have roughly ten noticeable birdies each (main receiver only).

I had previously taken notice of the comments on this reflector and in the
manual about shielding and good connections, so while building the rig I
made a special effort to make sure all connectors were firmly seated and all
ground screws were tight.  The mail list archives have a comment from one
fellow who improved his birdie situation by recalibrating the synthesizers,
but I tried that and it didn't make any difference.  Most of the relevant
postings suggested adjusting cable positioning.

So I popped the lid off the K3 this evening and (using a thin wooden dowel)
moved various cables around while listening to the birdies.  I was able to
make most of them completely go away by positioning the cables in one place
or another, but it was amazing to see how sensitive the placement was.  In
the case of one cable, literally a couple of millimeters made the difference
between an S4 birdie and ESP copy.  And it wasn't just making sure that a
particular cable was close as possible to a grounded shield or furthest from
some other point.  In some cases, the optimum position was a particular
distance from something ... it was like tuning an L-C circuit.

While I was at it I double checked every cable connector and they aren't the
problem ... wiggling them had no impact on the birdies.

I kept playing around with cable positioning until I got the best possible
combination.  In most cases, nulling the strongest birdies put almost all of
the weaker ones below the noise floor, but in a few cases nulling one birdie
made a different one stronger. Of the birdies I could previously hear on
20m, roughly 30 are now either gone or barely readable.  Of the remaining
ones, all except one are S1 or less.  I ended up with only one really
objectionable birdie hitting S4 on 14186.6.

I'm pretty sure that one or two of the cables are going to "relax" and shift
over time, so I'll probably see some of the birdies reappear, but in all
reality none of them are likely to be disruptive.  On CW I can use a narrow
bandwidth to make all of them go away, and on SSB the notch will do the
same.  And since they all tune so much faster than real signals, it doesn't
take too much to distinguish them and mentally ignore them.

Still, I'm wondering if this is normal behavior, or whether all these
birdies might be a symptom of something else out of whack.  Comments
appreciated.

73,
Dave   AB7E






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