February 8, 2012

KN-Q7A Single Band SSB Transceiver Kit - Step 3: Detector / Double Sided Band Modulator

This is the 6th article in our series on building the KN-Q7A Single Band 40m SSB Transceiver Kit.   In our prior article, we completed Step 2: the audio amplifier.  In this article we proceed with building step 3: Detector / Double Sided Band Modulator.

We followed the instructions and installed the parts.  Again, we would prefer a checklist of parts instead of working from the picture to figure out which parts to install.

We inadvertently installed a 103 capacitor in a location intended for a 104 capacitor.  We discovered this when we found we were short 1 103 capacitor.  We corrected this easily by de-soldering with the aid of a solder sucker and then re-soldering the part in the correct position on the circuit board.

KN-Q7A completed through step 3: Detector / Double Sided Band Modulator
To test the circuit we used our TH-F6A HT which as a wide-band scanner covering HF to check for the presence of BFO leakage on the IF crystal's frequency.  The instructions were written for a test assuming an IF crystal frequency of 8.465 Mhz.  Our kit used a 8.192 Mhz IF crystal and we detected a tone on our TH-F6A on 8.195 USB.  The signal was the strongest when nearly touching the antenna tip to the IF crystal. 

We placed our Tektronix oscilloscope probes across the IF crystal and found a waveform measuring about the same 8.192 Mhz.

We also used our speaker and plug assembly build in the prior step to confirm the audio amplifier section was still functioning properly.  Perfecto!

Lessons Learned
  • Hold down the jumper wire using a tool during install since it will become too hot to touch with a finger when soldering.
  • We would prefer to see the instructions list out the specific parts to be installed rather than trying figure it out from a photo only.
  • Take extra care with the 103 and 104 capacitors since they are easily confused during installation.
  • When testing for BFO leakage, dial-in the same frequency as the IF crystal.
In the next installment the fun continues as we proceed with building Step 4: RX IF Amplifier .

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