I'm very happy to see that you are digging into this so deeply.
Raj found that replacing the toroids at L5,L7 with sm1210 shielded inductors reduced coupling,
so they may work well here.? But at least we have a baseline fix, others can try variants.
>? The 470 ohms to 220 ohms is jacking up the gain by a few notches to drown out the 12 mhz spur.
>? Remember that the 12 mhz spur is not from the IF amp or the mixer, but from the Si5351's internal cross talk
If jacking up that gain at Q22 and Q42 fixes it, then the 12mhz we're worried about
must be riding along on clk2.? But jacking up that gain may further overload the D1,D2 mixer.
Since clk2 is always above 45mhz, seems a low pass filter on clk2 would be the better fix here.
I have not made measurements of my on on this stuff.
Just basing this on Allison's reports that the signals going into the mixers on transmit
are already too high (and that the LO injection levels are too low).
If we could use the BFO to select USB vs LSB, then clk1 could be parked high
at 45+12=57mhz, not flipping between 57mhz for USB and 45-12=33mhz for LSB.
Any residual 57mhz is easily filtered by the 30mhz LPF if clk2 is showing some crosstalk from clk1 also.
However, the current scheme of BFO always low is probably good enough so long as LSB is not used
on 15,12,10m bands since the transmit LPF's should take out the 33mhz.?
Assuming the transmit LPF's are working properly.
Flipping the BFO like that doubles our chances of the 12mhz Nano resonator harmonics
beating with BFO harmonics, creating audio tones.? ?Assuming that's where the tones come from.
But that issue needs to be fixed anyway, we have enough reports of audio tones already.??
The newer Raduinos now have a socketed Nano, and with Nano's so cheap
that at least allows us to try a bunch of different Nano's out if audio tones are a problem.
Just pushing some thoughts out.
I'm good with what works.?
Jerry, KE7ER
On Mon, Nov 12, 2018 at 05:56 AM, Ashhar Farhan wrote:
I am a little wary of axial inductors. I would have easily recommended air wound coils. However, given all the RF floating around, i would recommend a toroid.
?
The 470 ohms to 220 ohms is jacking up the gain by a few notches to drown out the 12 mhz spur. Remember that the 12? mhz spur is not from the IF amp or the mixer, but from the Si5351's internal cross talk
