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

[Kok Chen]

On Feb 10, 2009, at 2/10    9:09 AM, wayne burdick wrote:

> 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.

When you do this, will you be exposing the "real" 1st LO frequency  
through CAT?

Some of us are using the LP-PAN to receive and demodulate, while  
using CAT to move the transmit VFO around in the spectrum of the LP- 
PAN to zero beat a 2 kc baseband signal to the signal that is being  
demodulated.

As it is, there is already a problem with the SHIFT knob moving the  
1st LO frequency, but effect that can be discovered with CAT, and as  
long as SHIFT is not changed during transmission, it is workable.   
The real way out is to not use the SHIFT knob at all; we don't really  
need the shift knob when we implement our own DSP demodulators behind  
the LP-PAN.

If the 1st LO were to move by itself, we would need to know where  
these magic frequencies are. One possibility is that if you only plan  
to nudge the receive VFO, we can just keep our receive VFO fixed to a  
non-magic frequency and always tune the receiver by offsetting into  
the LP-PAN's output.

The best would be an option to be able to choose not to nudge the 1st  
LO.

Speaking of the SHIFT moving the 1st LO frequency, does the SHIFT  
knob also move where the birdies occur?  I haven't installed my  
second receiver yet and cannot perform the experiment.

73
Chen, W7AY