C1 has almost nil effect on BPF adjustment #qcx #bpf

Tony EI5EM

I have just completed a 40m version of QCX and when adjusting the BPF C1 has almost no effect. The rig receives fine but I would have expected a sharp peak . I have added and removed windings to and from the recommended 38 for the band. The other three settings using the three multiturn pots all have sharp minima when adjusted. Any recommendations de Tony EI5EM.

Howard K6IA

Hi Tony,

Did you try peaking C1 with the QCX connected to a dummyload?
In my case it was easier to see the peak.
To be honest I didn't find the peak to be that sharp but it was there.

As a side note I put my 40m QCX on the air last night during the ARRL DX contest to see how it would perform in those conditions.
I was very surprised how It good it was able to block out the close in strong signals. The side band nulling  worked great which can be an issue in SDR

Thanks Hans for the great design and fun build project!

Howard K6IA

Tony EI5EM

I didn't try with a dummy load just with no antenna connected Howard. I must try that.. Many thanks for reply de Tony EI5EM

Andy Kerrison

I had similar with my 40m build. 
What cured mine was resoldering the leads to the transformer windings.
i checked the continuity when I built it and was fine but when I was troubleshooting I found one pair had gone open circuit. 
Now it peaks nicely at a 9 as per manual. 

Good luck

Ryan NN7M

I’ll second Andy’s reply. My bpf reading was in the 3 or 4’s. And the trimmer capacitor had almost no effect on the bpf reading.

I put my finger on the largest torroid and the receive audio got much louder. I resoldered all of the leads to the board and my bpf reading was9. As the manual says, make sure your transformers are soldered correctly. 

Good luck