K3 Birdies

[David Gilbert]

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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[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: [hidden email] [mailto:[hidden email]] On Behalf Of David Gilbert
Sent: 10 February 2009 07:48
To: [hidden email]
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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[DC1RS]

Dave,

same thinge here with #1243 after installing the subreceiver.
A whole bunch of birdies appeared over the bands in main and subreceiver. I got rid of most of them by routing the cables and adding additional ground connections. I made the same experience that a millimeter could be the difference between barely audibe and S4. After 4 hours of playing around, managed to get almost all birdies barely audible, i closed the top cover and some of the birdies popped up to S4 again.
Quite frustrating...

73 de Roland, DC1RS

[David Cutter]

Roland

I would say VERY frustrating and I'm not looking forward to the exercise.  

Is there a procedure that anyone would recomend to reduce the iteration/iritation?

David
G3UNA

---- DC1RS <[hidden email]> wrote:

>
> Dave,
>
> same thinge here with #1243 after installing the subreceiver.
> A whole bunch of birdies appeared over the bands in main and subreceiver. I
> got rid of most of them by routing the cables and adding additional ground
> connections. I made the same experience that a millimeter could be the
> difference between barely audibe and S4. After 4 hours of playing around,
> managed to get almost all birdies barely audible, i closed the top cover and
> some of the birdies popped up to S4 again.
> Quite frustrating...
>
> 73 de Roland, DC1RS
>
> --
> View this message in context: http://n2.nabble.com/K3-Birdies-tp2301328p2302002.html
> Sent from the Elecraft mailing list archive at Nabble.com.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html

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