Since I have been testing a number of amplifier designs recently, I needed to be able to attenuate the output of my function generator to a lower level. To accomplish this, I decided to build a switched attenuator box to have some flexibility on the level of attenuation.

After designing the tuned IF amplifier, I wanted a second IF amplifier that handled most of the receiver's gain. This ended up being more of a learning experience than I anticipated.

Continuing along with my HF superheterodyne receiver project, I designed and tested a tuned IF amplifier to feed the crystal filter. The tuned IF amplifier determines the receiver's ultimate performance by providing stable, high-gain amplification and precise bandpass filtering.

When designing a superheterodyne receiver, terminating mixers properly is important. This is especially important for the second mixer which is responsible for converting the intermediate frequency (IF) into audio. Even at this stage of the circuit, maintaining a consistent 50 Ω termination across all frequencies is required to minimizing distortion products and maintain a high dynamic range.

In an RF receiver, a broad spectrum of signals is present at the input. Because of this, a narrow bandwidth filter is required to pick out only the desired signals. In the case of an amateur radio HF receiver, a bandwidth of 3 kHz is needed to receive single sideband (SSB) transmissions.

To optimize signal integrity and internal reflections within the HF superheterodyne receiver I am designing, I need to address mixing products. I tend to do this through the use of diplexers.

With my University Degree complete, I had much more free time to work on my superheterodyne reciever. Armed with more knowledge than my 2025 self, I decided it was worth redesigning most of it. Beginning with the frontend amplifier, I decided to try the cascode amplifier once again.

Among my radio equipment, the one tool I didn't have was a 50 Ω dummy load. Using a 250W rated RF resistor, I created a dummy load with a wattmeter made from an old VU galvonometer.

The previous cascode design was insufficient, so I redesigned it with much better results.

When testing the 20m superheterodyne reciever, there was a lot of noise generated by the previous frontend amplifier design, so I have decided to re-design the frontend amplifier. In this approach, I utilize the cascode configuration.

To amplify the IF portion of the 20m superheterodyne recievers signal chain, I though I would give the W7ZOI and K3NHI's termination insensitive amplifier design a try.

Still unsatisfied with my crystal filter, I decided to order some 8 MHz crystals. This decision ended up producing the best crystal filter for the reciever.

For the 20m superheterodyne reciever, I need two mixers for the RF-IF stage and IF-Audio stage. My initial diode ring mixer design functioned as intended, but this time I chose to make it more compact and to use different diodes. ~ I also built two this time.

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.

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.

With the ongoing superheterodyne reciever project, I designed and simulated a recieve amplifier to amplify the signals coming from the antenna. I have chosen to use a bipolar junction transistor in the common emitter configuration as my amplifier.

Lately I have been chipping away at the idea of creating a superheterodyne reciever (and potentially tranciever). One of the key blocks within the design of a superheterodyne reciever is a mixer. I have a number of options when it comes to mixer topologies, and among them I wanted to give the gilbert cell a look.