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A parallel resonant circuit is high impedance at your resonant frequency of 45mhz.
It will suck away any energy that is not 45mhz, such as the undesired 90mhz harmonic
during SSB operation.

When transmitting CW, we inject energy at the operating frequency into clk2, nothing coming
in from the IF stages, and that non-45mhz clk2 may be getting sucked away by your added filter.
Which could explain your loss of power when operating CW.

Farhan's LPF seems the better solution here.? However, note that clk2 frequencies
above the LPF's corner frequency will may be coupled back into the ~50 ohm IF bidi amp.
So clk2 may get attenuated a bit at operating frequencies above 58mhz-45mhz=13mhz
where 58mhz is the corner frequency of the new LPF.

Jerry, KE7ER


On Sun, Nov 18, 2018 at 07:22 AM, Ashhar Farhan wrote:

The parallel resonator will need much higher q to be useful. The filtering out of the 90hz will be quite nominal.

Have you swept this separately?

toggle quoted message. . .

?

On Sun, 18 Nov 2018, 20:12 iz oos <and2oosiz2@... wrote:

I have tried a slightly different solution for the spur. A screened 80nH tunable coil (like Coilcraft's) in parallel with a 150pf just across C22 and ground. These values should resonate at 45mhz and have a reasonable Q (greater than 2) to attenuate 90Mhz. However the CW power output dropped to just 5W (more than 3db loss then) on 40m so I have removed it. On SSB the power seemed less effected, why?

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