Project Introduction

General

This set of builders notes is under redesign due to the changes Tony has made to make for a combined kit with all of the components required to do any of the five available options (post 1 Jun1 2010).

The Softrock Lite II, the sequel to the SR Lite V6.2 series , provides an economical entry-level kit for the ham or SWL who wants to experiment with Software Defined Radio (SDR).

The Lite II circuit board size is 2.5 inches by 0.9 inches. All SMT components are mounted on the bottom of the board .

Ordering Information

Prices and availability of the kit are found at the Softrock Ordering Website.

This kit was originally offered in several versions, corresponding to bands of interest. It has, since, changed over to the Combined Lite II. This "combined" kit will include all components needed to build the kit as a 160m, 80m, 40m, 30m, or 20m receiver. The 15m option is no longer offered. The builder can decide which kit to build at commencement of the build; the parts for any of the options are included in the shipment. The Combined Lite II kit will be priced at $20 plus $1 for US postage or $2 for DX postage.

As of 11 June, 2010, the options in this series will include:

40m kit option (the example used herein)
• 40m kit will tune the following ranges:
• 40m when used with a soundcard that samples at 48 kHz - 7.032 to 7.08 MHz
• 40m when used with a soundcard that samples at 96 kHz - 7.008 to 7.104 MHz
• 80m kit option
  • 80m kit will tune the following range:
  • 80m when used with a soundcard that samples at 48 kHz - 3.49825 to 3.54625 MHz
  • 80m when used with a soundcard that samples at 96 kHz - 3.47425 to 3.57025 MHz
• 160m kit option
  • 160m kit will tune the following range:
  • 160m when used with a soundcard that samples at 48 kHz - 1.819 to 1.867 MHz
  • 160m when used with a soundcard that samples at 96 kHz - 1.795 to 1.891 MHz
• 30m kit option
  • 30m kit will tune the following range:
  • 30m when used with a soundcard that samples at 48 kHz - 10.100 to 10.148 MHz
  • 30m when used with a soundcard that samples at 96kHz - 10.076 to 10.172 MHz
• 20m kit option
  • 20m kit will tune the following range:
  • 20m when used with a soundcard that samples at 48 kHz - slightly below 14.024 to 14.070 MHz
  • 20m when used with a soundcard that samples at 96 kHz - slightly below 14.00 to 14.094 MHz
The 30m and 20m kits will all make use of 1/3 sub- harmonic sampling.

Prices for any one of the above kits are found at the Softrock Ordering site.

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Original Versions of SR Lite II

Before the current Combined SRLite II, the SR Lite II came in six versions corresponding to the 160, 80, 40, 30, 20, and 15m bands. These versions were described in the common schematic, which had a table of band-specific component values. The changes from that schematic to the current version are summarized below:

• Drop 15m option
• X1 now 14.089MHz for 80m.
• C8/C9 no longer band-specific; now 390 pF
• R7/R8 no longer band-specific; now 4.99k
• R5 and R6 are now band-specific (49.9Ω on 160, 80, 40; 10Ω on 30, 20)
• Toroids all go to T30-6
• New L1 and T1 winding info for all (all have same uH as original versions, except 30m T1, which goes to 0.18 uH)
• U4 no longer band-specific - it is LT6231 in all options

The original notes have been compiled into a PDF file by Philippe F6CZV for those who would prefer to have a single, printable source of the instructions.

Note: 8.215 MHz SoftRock Lite II for K3 IF application

Tony also offers a version of the Softrock Lite II kit that provides panadaptor capability on a K3 by tapping into the IF.

The SoftRock operates with the crystal frequency divided by 4. The SoftRock center frequency will be about 8.191 MHz and when used with a soundcard that can sample at 96 kHz will give IF band coverage from 8.143 MHz to 8.239 MHz where the K3 IF center is 8.215 MHz.

The kit is built very much like this kit, with the exception of the following changes:

• C10 100pF
• C11 not used
• L1 34T of #30 on a T25-2 core (4.0 uH)
• T1 9T of #30 on primary and 5T of #30 in each of the two secondary windings "bifilar" over the top of the primary on a T25-2 core (0.25 uH on primary)
• C3 = 100 pF
• C4 = 1500 pF
• Crystal X1 is 32.768 MHz

Theory of Operation

Many thanks to Jan G0BBL and Tony KB9YIG for their input to this and the stages' theoretical discussions.

• This receiver is patterned on the classic "direct conversion" receiver, in that it mixes incoming RF down to audio frequencies by, in effect, beating the RF against a Local oscillator such that the mixer products are in the sub 100 kHz 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.
• As a result, the (baseband) mixer products can vary in frequency from zero to +/- some theoretically high super-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 mixer's baseband 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 II achieves this by dividing the local oscillator's frequency by 4 (with attendant phase shifts to achieve quadrature).
• The output of the divider chain is two signals, I (In-Phase) and Q (Quadrature), identical in all respects but phase i.e., they are "in quadrature").
• RF from the antenna is bandpass-filtered for the band that is specific to the kit.
• The two quadrature signals from the Divider stage are fed into the mixer stage, which mixes the bandpass-filtered RF down to two baseband signals that are also in quadrature and otherwise identical to each other.
• These two signals are provided to an amplifier stage where they are amplified and low-pass filtered 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 baseband signals 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 48 kHz spectrum. Soundcards capable of higher sampling rates (e.g. 96 kHz or 192 kHz) will yield proportionately wider bandwidth, provided their internal audio filters do not cut off the higher audio frequencies.
• Mike Collins KF4BQ (whose photos of the completed board are found further on in this page) has performed extensive tests on this receiver and has found it to be an exceptionally powerful receiver. Considering the cost, nothing out there can beat it!

(go directly to build notes)

Project Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

(above schematic has clickable areas that can be used for navigation)

(go directly to build notes)

Project Bill of Materials

See Project Bill of Materials

Project Expert's (terse) Build Notes

Board Top

Board Bottom

Summary (Experts') Build Notes

10 June 2010: The latest schematic from Tony is available at this link. This schematic combines the schematics for the various options into a single schematic.

• Conduct BOM inventory. Note: the inventory covers all options, so there will be parts left over at the end of the build. Also note that some items in the inventory are expected to be builder-furnished (e.g., hookup wire, power cables, etc.
• Install all SMT Caps (bottomside)
• Install SMT ICs (bottomside). Note: you should install the 16 pin U3 BEFORE installing the 14 pin U2.
• Install 17 topside resistors. Note R7 and R8 are band-specific
• Install 12 topside ceramic capacitors (6 of which are band-specific)
• Install topside Semiconductors and IC (U1, D1, Q1, Q2)
• Install topside band-specific crystal and grounding lead
• Install and wind topside band-specific inductors (L1 and T1)
• Make external connections
• load and run Rocky and test the radio

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 Divider Stage
• Build and Test the Operational Amplifiers Stage
• Build and Test the Band Pass Filter Stage
• Build and Test the Mixer Stage
• Build and Test the External Connections Stage

Background Info

Tools

Winding Inductors

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.

Soldering

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

View the above in full-screen mode on Youtube.

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:
  • 
    Velleman VTSS5U 50W Solder Station (approx $20 at Frys)
  • 
    Haakko 936 ESD Solder Station (under $100) 

ESD Protection

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.

Work Area

• 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.

Misc Tools

• 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

Project Testing

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.

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.

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