Saturday, March 1, 2014

Minima - BFO Mixer

I have started working on the next Farhan Minima Module for my experimental receiver (see previous post). This module will be the BFO Mixer which is used for SSB Modulation and Detection.

The circuit and layout is simple and will use the same SMA connectors as my previous constructed modules.
Proposed BFO Mixer

My proposed BFO Mixer board will 1x1.2 inches, which is laid out with DipTrace.

Farhan's Minima Transceiver requires for two 1N4148 Diodes for the mixer. He suggests that the diodes should be matched, and provided a test fixture and procedure to help find a matching pair.

I have several old 1N4148 Diodes from which to pick from, but I decided to order a fresh batch which hopefully will be manufactured from the same processing batch.

While looking for Diodes to order, I discovered the 1N4148 is manufacture as a SOT-23 MMBD4148 (single diode), and a dual diode as MMBD4814SE. Of course, for my projects I am always looking for the smallest package(s) available, and with two diodes in one package this part is a big win. This diode is available in four configurations; single diode, dual common cathode (CC), dual common anode (CA), and dual one of each (SE). To meet Farhan's circuit connection requirements, my BFO Mixer will use the SE configuration.

I tried to find information about the manufacture of this dual diode, that is; I wanted to know if the two diodes are from the same die, or if they are just two chips put into a common SOT-23 package. The information was not found. I am hoping the two diodes will be a matched pair.

I think the dual diode part will work fine for my project. More details to follow.

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