On Mon, Feb 1, 2021 at 09:27 AM, Gregg Myers wrote:

I don't think of the tone I hear as a birdie as such (which I think of as appearing as a fictitious signal at isolated fixed frequencies)

Maybe "birdie" is not the right word to describe this...

as the low tone does not depend on what frequency I am listening to but is constant across the band frequencies.

Mine did too, except, when I switched to Split VFO mode or RIT mode.  In these modes you are changing the Receive only frequency while the XMIT frequency is Not updated.  In these modes, as I tune by 100Hz steps, I can hear many tones in different places.  Usually loudest with VFO A tuned 500 to 800 hertz higher than VFO B.

My current thinking is that it is either leakage within the si5351a itself

That's my opinion too, as all three of my QCXs have the same issue at different audio levels...  even though they are on different bands, and mini's layout is quite different than the QCX+.


Do you hear the same tone across the band when you're in VFO Split Mode?


Thanks,
km6wt

On Mon, Feb 1, 2021 at 02:28 PM, Gregg Myers wrote:

BTW, as I checked on my mini, the transmit frequency (Clk 2) is not outputting anything unless you are actually transmitting (ie. Clk2 only 'turns on' during transmit),

Yes, that's what I'm seeing too.  And your right, Clk 2 output is turned off, so nothing when scoping Clk 2 pin.

although internal to the chip the multisynths are likely doing their thing all the time. So as best I can guess, I am hearing some of the multisynth oscillator leakage or interference.

Yes, I agree, it must be some kind of crosstalk inside the chip...  And since it happens in all 3 of my QCXs it's likely an issue inherent in the Si5351a chip itself and just needs to be programmed to be avoided.


If you scope Clk 0, you will see that it changes frequency to 25MHz during transmit, and back to operating frequency during receive.

Maybe Hans can do something similar to Clk 2.  
For example:

1. During receive (key-up)
   
   1. set Clk 2 off
   2. set Clk 2 frequency up 10MHz (or just off somewhere out of the way)
2. During transmit (key-down)
   1. set Clk 2 back to transmit frequency
   2. set Clk 2 on

I wonder if Clk 2's freq shows up on a logic analyzer while scoping Clk 0 or Clk 1....


Thanks,
km6wt

There are actually several tones in Gregg's recording.  There is one tone there when the recording starts, a second tone starts at about 4 seconds in, a third tone starts at about 12 seconds in, and I think another starts at about 15 seconds in (but it's so weak I could be imagining it).  Not sure if that means anything, but that's what I observed.