[Elecraft] K3 Birdies: firmware-based fix in progress

[David Gilbert]

That's very interesting.  I found that I can accomplish much the same 
thing on CW by simply using a very narrow bandwidth (250 Hz in my case) 
... the birdies tune so fast that they drop outside the passband with 
just a minor shift in VFO frequency.

I don't use SSB as often, but there the notch filter has been 
effectively plinking the birdies.

73,
Dave   AB7E



wayne burdick wrote:
> The K3 is a down-conversion superhet that uses high-level signal 
> injection to achieve its excellent dynamic range. Short of adding many 
> more pounds of shielding and elaborate cable dressing, there's no way 
> to completely eliminate the few spurious signals that rise above the 
> noise floor.
>
> These "Fast-tuning" birdies result from UHF harmonics of the signal 
> sources that leak back into the main mixer. In some cases they combine 
> and end up in either the I.F. or R.F./image range of the receiver. 
> Typically, they involve 9th-order or higher harmonics of the VFO. 
> That's what makes them "fast": if you move the VFO 100 Hz, the pitch of 
> the birdie will shift on the order of 1 to 2 kHz.
>
> While it is possible to attenuate some spurious responses by moving 
> coax cables around, there is a firmware-based approach that we're 
> working on. The general idea is to shift the 1st LO and BFO a small 
> amount, simultaneously, when the VFO is tuned to specific frequencies. 
> If the shift is small relative to the communications bandwidth in use, 
> it will hardly be noticeable when the VFO is tuned over a "mapped out" 
> spot in the tuning range.
>
> I have this new firmware nearly completed, and in early tests, it 
> appears to work very well. Fast-tuning birdies that are mapped out 
> pretty much disappear as the VFO is tuned over them. The upshot is that 
> you can have your cake (outstanding dynamic range in a rig that weighs 
> less than 10 pounds) and eat it, too (no annoying birdies).
>
> If you'd like to try a field-test version of K3 firmware that includes 
> this new feature, please e-mail me directly.
>
> 73,
> Wayne
> N6KR
>
> ---
>
> http://www.elecraft.com
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/elecraft/attachments/20090210/3e37fc4e/attachment.html