BITX20A SSB Transceiver
Assembly, Testing, and Operation
Arv – K7HKL
This article documents assembly, testing and operation of the Hendricks QRP Kits BITX20A SSB transceiver. This kit is based on an original BITX20 design by Farhan. Several improvements to the original design have been documented in posts on the BITX20 Yahoo Group, with further BITX20A kit design refinement and testing performed by Dan Tayloe – N7VE and Jim Kortge – K8IQY.
Assembly is divided into functional modules with testing of each module as it is completed. This assembly and testing sequence is:
1.Receive AF section
2.Transmit AF amplifier
3.BFO / Carrier Oscillator and associated mixer
4.Receiver 2nd IF
5.Transmitter 1st IF
7.Receiver 1st IF
8.Transmitter 2nd IF
9.VFO and RF mixer
10.Receive and Transmit low-level RF amplifiers
11.RF Bandpass Filter
12.Transmit RF PA section.
Before starting construction, there are some techniques that should be reviewed to help insure quality of the finished kit:
Soldering will be mostly PCB based. For this you will need a 25 watt or similar soldering iron with a small tip. If your soldering iron is not temperature controlled, you might want to add a conventional full-wave lamp dimmer to it's AC socket so you can manage the temperature.
DO NOT USE ACID-CORE SOLDER.
Soldering iron tip cleaning is necessary to allow quick soldering without overheating PCB pads and components. Use a dampened sponge or course steel wool type tip cleaner.
Most of the resistors will be installed vertically on the PCB. To make this look professional and to help avoid shorts or damaged components, you should bend one lead of these components over the edge of a PCB to make a consistent and visually appealing shape. It helps future trouble shooting to always make this bend in the most significant digit end lead so that the color code is always read top-down.
When installing components, install a few (usually 4 to 10) and then solder these before proceeding. After each soldering session, clip any excess lead length with small wire cutters and inspect each connection for shorts, cold solder joints, or other errors. Re-solder those connections which look like they might not be adequate. It helps to use a magnifying glass to check for soldering errors.
When you unpack the kit component bags, it helps to sort and compare what you have received with the BOM (Bill Of Materials). If you have a block of Styrofoam packing material you can insert one lead of these components in that as a way to keep them separated into sorted groups. This makes it much easier to find a specific component when assembling your kit.
If you have to unsolder and re-solder components on the PCB, it is much easier if you use a wooden toothpick (the round kind work best) to re-open holes in PCB pads.
Some sort of PCB holder makes circuit assembly much easier. Hendricks QRP Kits sells one such unit (www.qrpkits.com/pcbvise.html), but you can also use other manufacturer's units, or even manufacture your own homebrew PCB vise
Next blog entry will be start of actual BITX20A construction.