With the new crystals characterized, I take on a new approach to designing a crystal filter.

To effectively build a Crystal filter, I characterized the new 4 MHz crystals I ordered. Using two methods, the NanoVNA-H with DiSlord firmware, and the G3UUR method.

After a dissapointing first attempt, I redesigned the crystal filter again. This time using a slightly different approach.

The next step in building my 20m superheterodyne reciever is the crystal filter. This filter will determine the selectivity of my radio's tuning and dynamic range. The goal is to make a crystal filter with a bandwidth of 3 kHz for SSB operation.

To prevent any strong out of band signals from overloading the frontend of my reciever, I designed a bandpass filter to place before the rf amplifier.

The next key component of my 20m Superheterodyne Reciever project was the mixer. In a previous post I did some experimentation with a Gilbert cell mixer, which yielded promising results, but there is a simpler approach that requires less components. This brings us to the double balanced diode ring mixer (or double balance mixer, DBM for short).

After the two previous designs, I decided to purchase some transistors rated for a higher frequency. This is a more pay-to-win approach to my previous issues, but works nonetheless. An additional bonus is the noise figure of the new transistors being significantly lower.

At my PC I usually use headphones and an FX-Audio DAC to listen to audio, but occasionally I will hook up my JBL partybox to play music with a speaker. The issue I was having was that the line level output from the DAC was at a fixed volume. So as a small, simple, 1 hour project, I made a stereo volume knob for the line level output.

Learning about the NanoVNA, I found that testing amplifiers without any attenuators resulted in terrible resutls. Because I want to test my amplifier designs using the NanoVNA, I made some simple 50 ohm attenuators.

Having acquired more knowledge on amplifier configurations and properties, I redesigned the front-end amplifier. This time using a common base as the first stage, then common emitter as a second stage, with a common collector at the output to match the impedance to 50 ohms for the VNA measurements.