20.1 MHz mixer filter and buffer amplifier
I still needed to filter and amplify the TUF-1 mixer output to make a usable 20.1 MHz local oscillator for my Jupiter receiver. I didn’t have a lot of board space left and had to compromise.
Above — Post mixer filter amplifier sandwich. I’ve never tried this before in a post-mixer filter scheme and ran T68-6 toroids [ should have run size 50 or less ‘roids to save space ]. At some point I must have shorted and fried the MPSH81 and had to clip it out of the crammed board and replace it. This oscillator project fought me from start to finish.
Frequency domain analysis of the entire 20.1 MHz local oscillator output. All non-20.1 MHz tones are down by at least 54 dB. Not great for me, but OK. Prior to placing the board in its metal box, the LO and RF tones were down closer to 60 dB, but the metal box de-tuned, and/or de-Q’ed my T68-6 filter resonators.
Lacking both time and patience to spend more time wrestling with this oscillator. I just bolted the lid on and sighed in relief when it was done.
The 16.93 MHz LO tone is especially tough to filter since it’s close to the IF. A 16.93 MHz notch filter might be employed downstream from the oscillator box. The output power = -6.79 dBm.
Above — The final box. A lot of work and parts for a simple 20.1 MHz VFO! It might be better to make a synthesizer with a Si5351A or a VXO affair, but I went my own long way.