[Elecraft] K3 birdies - question?

[David Gilbert]

I've played around extensively with the cables in the K3 to see what 
worked best, and as others (including Wayne) have noted, cable positions 
that minimize one birdie might be poor for another.  I'm convinced it 
also makes a big difference whether or not you have the KRX3 subreceiver 
installed, and I suspect that some signals are being conducted by the 
shield of the KRX3 itself.  I can short the top of the KRX3 shield to 
the chassis at its far rear corner (looking from the front of the rig) 
and cut the strength of several birdies in half. 

I agree with Ron, though, that routing the cable to J85 on the KRX3 is 
best done under the mixer board ... that made a large difference on 
certain birdies without adversely affecting others that I could tell.

The other cable that seemed to have a big impact for me is the one going 
from J2 on the KREF3 board to J83 on the KSYN3 board.  Some birdies are 
weakest when that cable is pressed down closer to the main RF board, but 
it makes others stronger.  Most of the birdies are weaker when that 
cable is positioned just barely on top of the KRX3 shield ... running 
along the front corner as closely as possible for as far as possible.  I 
noticed while playing around with that cable that if I held it between 
the thumb and index finger of each hand that I could almost totally mute 
certain birdies that were otherwise a solid S-2.  So, in an experiment 
I'm somewhat embarrassed to acknowledge, I placed 4" x 6" sheets of 1/8 
inch thick high density conductive anti-static foam inside zip-lock 
sandwich bags (to avoid shorting anything in the K3) and tried to 
isolate that and other cables from each other and from various parts of 
the K3 with what I thought might be lossy shielding at UHF frequencies.  
Rolling up some of the foam into about a one inch diameter roll and 
placing it between the cable going to J2 of the KREF3 board and the 
KREF3 board itself significantly cut several 40m birdies down in 
strength, but it didn't affect the S-3 one at 7259.48 at all.  I 
abandoned the foam and repositioned the cable along the front edge of 
the KRX3 shield.

One thing I noticed, though, was that the can for the KTCXO (plugged 
into a socket on the KREF3 board) was extremely sensitive.  If I touched 
it with my finger the strength of the birdies increased dramatically.  I 
assume the can is supposed to provide shielding and is probably grounded 
via one of its pins, but it sits pretty far off the socket and I'm 
wondering whether it shouldn't be more effectively bonded to ground.  I 
built a K2 several years ago and if I remember correctly the 
instructions required that the cans of the crystals be grounded with 
wires that I soldered to them.  I'd be willing to try bonding the can of 
the KTCXO to ground with some sort of clip if anyone from Elecraft can 
tell me that I won't ruin something doing so.

I've had the chance to beta test the SIG RMV birdie removal software and 
I find it works very well.  I purposely left a half dozen birdies 
untreated so that I could check out other potential remedies such as the 
(ahem) conductive foam, but at this point I've gone back and zapped them 
with SIG RMV and I'm happy with that.  My advice to others would be to 
position the cables as best you can per the descriptions that have been 
given by others here on the reflector, and then use SIG RMV to finish 
the job when it becomes universally available.  Since SIG RMV alters the 
frequency of the birdie itself as you tune across it, it totally removes 
the birdie ... it doesn't just weaken it.  It's a very clever piece of 
engineering.

If anyone is interested in seeing my cable routing as a starting point, 
the links below might help.  I make no claim whatsoever that they will 
work for anyone else.

http://i228.photobucket.com/albums/ee141/xazdave/K3CableRouting1.jpg

http://i228.photobucket.com/albums/ee141/xazdave/K3CableRouting2.jpg

73,
Dave   AB7E






Ron D'Eau Claire wrote:
> I've had the cables all over the place. There seems to be only one cable
> whose placement has a significant effect on birdies. That's the long
> (10"/25cm)cable running from J84 at the bottom of the Auxiliary KSYN3 board
> to J85 on the KRX3 RF module. It should be dressed as shown in Figure 47 in
> the KRX3 manual. In some cases it helps to keep it away from the tiny
> toriods on the mixer board as well. Either run it across above the mixer
> board as shown or work it down under the mixer board so it loops up between
> the mixer board and the front panel shield to J85 on the KRX3 RF module.
>
> Ron AC7AC 
>
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ian White GM3SEK
> Sent: Wednesday, March 04, 2009 12:11 AM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 birdies - question?
>
> James Sarte wrote:
>   
>> At first I thought I did not have any noticeable birdies, but now it 
>> seems that I have developed a few.  It's probably from moving cables 
>> and such around inside the rig.
>>
>>
>>     
>
> We could really use a detailed set of photos of cables behind the synth 
> board(s), showing the complete step-by-step buildup of a good layout  - 
> and also examples showing what *not* to do.
>
>
>
>