[Elecraft] K3 chirp in cross-band split

[Bill W4ZV]

Nick-WA5BDU wrote:
> 
> I worked special Armed Forces Day station AAZ today as I transmitted on 
> 14.050 and listened on 13.507.  A guy emailed later that my signal 
> sounded "interesting" so I monitored it with a separate receiver and 
> sure enough it was chirping like my old Heath VF-1 VFO.
> 
> I'm not sure if this is expected behavior or not so this is more 
> observation than complaint.  I don't have the sub-receiver.  
> Experimenting a little, when I turned off both the QSK and VOX 
> indicators and used the XMIT button to go into the transmit mode, there 
> was no chirp.
> 

Here's the fix from Wayne (not sure why this isn't on the mods webpage):

It turns out that the DDS signal driving the PLL may be at too low an
amplitude at some DDS frequencies. The apparent cure is to increase the gain
of the buffer that follows the DDS crystal filter (Q6). This has no negative
impact on synth characteristics, but it does square up the signal nicely so
that the PLL chip is properly driven.

Mod details:

1. It would be helpful if you can find a slight chirp first, so you can do a
before/after comparison. But you should make the mod even if you can't find
a chirp, then test to make sure it isn't worse (!).

2. Make sure you install firmware rev 3.66, which has a slight change to the
T/R switch associated with the mod.

3. Add a 51 to 56-ohm resistor across R20 on just your main synth (the sub
synth isn't involved in T/R switching). It can be 1/4w or 1/8w, leaded or
SMD. It has to be kept close to the PCB so it won't hit the front shield
when the synth is reinstalled.

73,  Bill

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