Simple Homebrew SSB Base Rig Part 6 - IF Amps and Crystal Filter

Quick run down on the design of the IF amps and matching transformers. The radio is now a single conversion superhet configuration.

22 Dec 17. Did some more tests and reduced the gain of the two IF amps by changing the emitter decoupling capacitor to 470pF.

Not shown in the video was the Arduino C++ code to generate the VFO and BFO frequencies. The crystal filter has a center freq of 9.011500MHz and an assumed BW of 2.7kHz. As 80m is LSB, the VFO freq (Si5351 CLK0) was set to be 9.011500MHz + 1500Hz - Received Freq. This places the suppressed carrier of the received signal just above the passband of the crystal filter, and thus, places the LSB intelligence within the passband of the filter.

The BFO freq (Si5351 CLK2) was set to be 9.011500MHz + 1500Hz in order to mix the LSB intelligence in the product detector down to baseband (audio).

Arduino Code

[ryersong]

Thank you, particularly for the step by step paper calculations.

[Avrora]

Hi Charlie! Can you please explain to me? 10:11 At the middle of the page you have calculation for 500:50 transformer. Inductance Xl = 712 and Xl = 7144. It is ok, I understand. But what is it 200 and 2000?
Oleg, UR7WKH

[russoft]

Hi Charlie. In place of the crystal filter module, I assume one could build up a crystal ladder filter with a few crystals? I'm trying to build on a shoestring budget so don't want to buy a crystal filter but have access to the test equipment to build my own. I assume selection of IF frequency isn't too critical (I can't source 9 MHz crystals as cheaply as 10 MHz).

[berndb.]

Hello Charlie,
Thank you for presenting your concept. I am always very happy about a new video of your projects. I'm looking forward to the next. Maybe even before Christmas? ;-)
Unfortunately I did not get any further with my TRX. At the moment it looks on the qrl as if there would be no next year. A lot to do....

73 Bernd