'SP-2B2C' is a project to design, build and document in a video series the design and construction of a two band (40 and 20m) crystal locked (channelised) QRP CW transceiver.
The rig is entirely scratch-built, from 'borrowed' designs, circuit elements and ideas. It is a compact, neat pocket rig that will provide more than adequate service as a simple parks and portable rig, but it comes into its own for SOTA where the crystal-locked channels will not be a major impediment to making contacts.
Frequency control is provided by separate dedicated and trimmed 7MHz and 14MHz crystal oscillators with buffers and with a fixed transmit offset.
The receiver is a conventional Direct Conversion design with strong band pass filtering and an SA612 mixer, followed by a dual op amp for audio filtering and gain, and an LM386 for headphone or speaker listening. It has ample gain both in the shack and on a windy summit.
The transmitter duplicates a significant part of the popular QCX and MTR radios using a high speed logic gate as a digital driver, to three BS170 FETs in parallel for a full 5 watts on both bands. Keying for a straight key is done using discrete components.
The receiver draws about 50mA and the transmitter up to 0.8A on key down. Band switching is done with two miniature telecom relays.
Schematic: vk3hn.files.wo...
Blog: vk3hn.wordpres...
Part 1 - Concept
Part 2 - Receiver PCB
Part 3 - Receiver Band Pass Filters
Part 4 - Receiver build & test
Part 5 - Tx PCB, keying, pre-driver, LPFs
Part 6 - Transmitter driver
Part 7 - Transmitter PA and tests
Part 8 - Case assembly and field test
22 окт 2024
