GeneralThe Softrock Lite V6.2 series provide an economical entry-level kit for the ham or SWL who wants to experiment with Software Defined Radio (SDR). As of 10/26/2008, the offerings in this series are (links are to schematics in Yahoo Groups files folder):
40m kit option (the example used herein)
- 40m kit at $10 US/Canada and $11 for DX will tune the following ranges:
- 40m when used with a soundcard that samples at 48 kHz - 7.032 to 7.08 MHz
80m kit option
- 80m kit at $10 US/Canada and $11 for DX will tune the following range:
- 80m when used with a soundcard that samples at 48 kHz - 3.504 to 3.552 MHz
160m kit option
- 160m kit at $10 US/Canada and $11 for DX will tune the following range:
- 160m when used with a soundcard that samples at 48 kHz - 1.819 to 1.867 MHz
Upgraded 30m kit option
- 30m kit at $12 US/Canada and $13 for DX will tune the following range:
- 30m when used with a soundcard that samples at 48 kHz - 10.100 to 10.148 MHz
Upgraded 20m kit option
- 20m kit at $12 US/Canada and $13 for DX will tune the following range:
- 20m when used with a soundcard that samples at 96 kHz - slightly below 14.00 to 14.094 MHz
Upgraded 15m kit option
- 15m kit at $12 US/Canada and $13 for DX will tune the following range:
- 15m when used with a soundcard that samples at 96 kHz - slightly below 21.00 to 21.092 MHz
Note that the components shown in thes builders' notes are for the 40m option. The Bill of Materials provides a chart depicting the components that are band-specific and shows their values. If you are building the kit for one of the other options/bands, you should refer to this chart.This kit has been retired. Its replacement is the SR Lite II
- This receiver is patterned on the classic "direct conversion" receiver, in that it mixes incoming RF down to audio frequencies by beating the RF against a Local oscillator such that the mixer products are in the audio frequency range.
- Unlike the traditional DC receiver, the SDR does not "tune" the local oscillator's frequency to beat up against a desired RF signal. Instead, the local oscillator is at a fixed frequency. This fixed oscillator frequency is referred to as the "center frequency".
- As a result, the mixer products can vary in audio frequency from zero to +/- some theoretically high audio frequency. In fact, the practical limit is one-half the soundcard's maximum sampling rate.
- The "tuning" (and demodulation and AFC and other neat radio things) happen in the software part of the Software Defined Radio. It is the magic of Software that makes for the extraordinarily high selectivity in the direct conversion hardware (which is notorious for great sensitivity but terrible selectivity).
- The software requires the AF mixer products to be provided to the PC as two separate signals, each identical to the other, except that they are 90 degrees apart in phase ("in quadrature"). The SR Lite achieves this by setting the local oscillator to a frequency that is 4 times the desired center frequency and then dividing that frequency 4 times (with attendant phase shifts to achieve quadrature).
- The output of the divider chain is two versions of the center frequency, identical in all respects but phase.
- The two center frequency signals are in quadrature and are fed into the mixer stage, which mixes the RF down to two audio signals that are also in quadrature.
- These two signals are provided to an amplifier stage where they are amplified to levels acceptable to the PC's soundcard stereo line-in inputs.
- A soundcard which can sample 48 kHz, can digitize an incoming "chunk" of audio frequency from 0 to 24 kHz. Such a soundcard, using its stereo line-in inputs for the I and Q signals, will yield an effective bandwidth of 48 kHz: 24 kHz above the center frequency and 24 kHz below the center frequency. The SDR software in the PC manipulates the digitized I and Q signals to deliver, demodulate, condition, and filter signals within this bandwith.
(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)
(go directly to build notes)
Project Bill of MaterialsSee Project Bill of Materials
Project Expert's (terse) Build Notes
See Tony's original builders notes
Project Detailed Build Notes
For the non-expert builders among us, this site takes you through a stage-by-stage build of the kit. Each stage is self-contained and outlines the steps to build and test the stage. This ensures that you will have a much better chance of success once you reach the last step, since you will have successfully built and tested each preceding stage before moving on to the next stage.
Each stage is listed below, in build order, and you can link to it by clicking on its name below (or in the header and/or footer of each web page).
- Inventory the Bill of Materials
- Build and Test the Power Supply Stage
- Build and Test the Local Oscillator Stage
- Build and Test the Dividers Stage
- Build and Test the Operational Amplifiers Stage
- Build and Test the BPF Stage
- Build and Test the Mixer Stage
- Build and Test the External Connections Stage
To learn how to wind coils and transformers, please read the
- tips from the experts and then
- view the excellent videos on KC0WOXs Website
- or take a read of Dinesh's VU2FD guidelines.
- You can review the common construction techniques for inductors for details on toroidal and binocular inductors.
If you are not experienced at soldering (and even if you are somewhat experienced at soldering), refer to Tom N0SS's excellent tutorial on basic soldering techniques.
The video below describes techniques for soldering SOIC 14 (and 16 and 8) SMDs
For the more adventurous, there is a process using solder paste and an electric oven called the reflow process, which can be used to install all the SMT chips to one side of the PC Board. This is documented by Guenael Jouchet in the following Youtube segment:
- Read the Primer on SMT Soldering at the Sparkfun site. It is a very good read and it speaks great truths. Then take the time to watch the video tutorial on soldering an SOIC SMD IC.
- Solder Stations. Don't skimp here. Soldering deficiencies account for 80 percent of the problems surfaced in troubleshooting. It is preferable to have an ESD-safe station, with a grounded tip. A couple of good stations that are relatively inexpensive are:
You may wish to review the message topic beginning at Message 43554 for a common-sense discussion on ESD.
- Avoid carpets in cool, dry areas.
- Leave PC cards and memory modules in their anti-static packaging until ready to be installed.
- Dissipate static electricity before handling any system components (PC cards, memory modules) by touching a grounded metal object, such as the system unit unpainted metal chassis.
- If possible, use antistatic devices, such as wrist straps and antistatic mats (see Radio Shack's Set for $25 or the JameCo AntiStatic mat for $15)).
- Always hold a PC card or memory module by its edges. Avoid touching the contacts and components on the memory module.
- Before removing chips from insulator, put on the wrist strap connected to the ESD mat. All work with CMOS chips should be done with the wrist strap on.
- As an added precaution before first touching a chip, you should touch a finger to a grounded metal surface.
- If using a DMM, its outside should be in contact with the ground of the ESD mat, and both leads shorted to this ground before use.
- See the review of ESD Precautions at this link.
- You will need a well-lit work area and a minimum of 3X magnification (the author uses a cheap magnifying fluorescent light with a 3X lens. This is supplemented by a hand-held 10 X loupe - with light - for close-in inspection of solder joints and SMT installation.
- You should use a cookie sheet or baking pan (with four sides raised approximately a half an inch) for your actual work space. It is highly recommended for building on top of in order to catch stray parts, especially the tiny SMT chips which, once they are launched by an errant tweezer squeeze, are nigh on impossible to find if they are not caught on the cookie sheet.
- It is most important to solidly clamp the PCB in a holder when soldering. A "third-hand" (e.g., Panavise or the Hendricks kits PCB Vise) can hold your board while soldering. In a pinch, you can get by with a simple third-hand, alligator clip vise. Jan G0BBL suggests "A very cheap way is to screw a Large Document Clip to a woodblock which will clamp the side of a PCB."
- Magnifying Head Strap
- Tweezers (bent tip is preferable).
- A toothpick and some beeswax - these can be used to pickup SMT devices and hold them steady while soldering.
- Diagonal side cutters.
- Small, rounded jaw needle-nose pliers.
- Set of jewelers' screwdrivers
- An Exacto knife.
- Fine-grit emery paper.
Project Completed Stage
Top of the Board
Bottom of the Board
Each stage will have a "Testing" Section, outlining one or more tests that, when successfully completed, provide you with the confidence and assurance that you are heading in the right direction towards a fully tested and built transceiver.
When you perform a test, you should always record the results of the test where indicated in the Testing section. This will make troubleshooting via the reflector much easier, since you will be communicating with the experts using a standard testing and measurement regime.
When comparing measurements to those published in these notes, the builder should be aware that actual and expected values could vary by as much as +/- 10%. The idea behind furnishing "expected/nominal" measurement values is to provide the builder with a good, "ballpark" number to determine whether or not the test has been successful. If the builder has concerns about his measurements, he should by all means pose those concerns as a query in the Softrock reflector so the experts can provide assistance.
This kit can be built and reliably tested using nothing more than a common multimeter. Tests assume that the builder has a decent digital multimeter of sufficiently high input impedance as to minimize circuit loading issues. Measurements will be taken of current draws, test point voltages, and resistances.
Most stages will have a current draw test, in which the builder tests the stage's current draw in two different ways:
- First, testing the draw through a current-limiting resistor
- Then, when that test is OK, removing the current-limiting resistor and measuring the real current draw.
You can always use Rocky to generate I and Q signals for tests requiring these audio signals (this is the author's preferred way)