Ensemble RX Home Introduction

General

Retired Kit

This kit is the earlier, now retired Ensemble RX version. These instructions are provided for those who possess and might have delayed building that version of the Ensemble RX kit. The latest version is the Ensemble RX II. Kit.

The Ensemble RX kit and its 4.5: X 2" board represent the culmination of a long line of Softrock SDR receivers from Tony Parks, KB9YIG. The line began with the Softrock 40 RX and went through several iterations of receivers. The most recent receiver was the All-band receiver with an add-on automatically switched bandpass filter. This current kit is a considerable refinement on that kit and streamlines the kitting process for Tony.

The Ensemble RX kit provides coverage of ham bands from 160-10m, in four different optional "super bands" (each with underlap and overlap within the parameters of the associated bandpass filter):

1. 160m - Continuous coverage from 1.8 to 2.0 MHz
2. 80m and 40m - Continuous coverage from 3.5 to 7.3 MHz
3. 30m, 20m, and 17m - Continuous coverage from 10.1 to 18.168 MHz
4. 15m, 12m, and 10m - Continuous coverage from 21.0 to 29.7 MHz

The band coverage is via 4 switchable "bands" ("superbands"). Band switching is performed under program control, in conjunction with programmatic control of the receive frequency. This control is provided by an Atmel ATTiny85 micro-controller, acting as a USB device to control the Si570 programmable oscillator and automatically switch to the appropriate band (0-3) as the frequency changes.

As a welcome improvement over other models, this kit provides pcb-right-angle jacks for all external connections: Antenna, USB from the PC, I/Q output to the PC, and Power to the Board. Thus, once built, the kit can be placed in a suitable enclosure and handled thereafter as a "blackbox peripheral" to the PC.

The design of the Ensemble RX is very similar to the receiver design of its sibling Ensemble RXTX. The major difference is the greater band coverage of the Ensemble RX kit (roughly 4 "superbands" on the RX vs. 1 "superband" on the RXTX).

This kit is an excellent value for both the licensed amateur and the SWL who is comfortable with building electronics kits. The skill level and experience requirements are medium-level because of the small size of the components, the requirement to be able to solder SMT parts, and the requirement to wind and install inductors. Thousands of builders have proven this is not an insurmountable set of requirements. If you are new at this, you should try one of Tony's sub $20 monobander RX kits as a "starter/learner" kit.

Several hams have provided interesting/informative galleries of photos as they have followed these build notes:

• Ulf, K1ULF

Recommended Enclosure

Tom KM5KH offers a very nice enclosure for the Ensemble RX line.

Theory of Operation

Basic Theory

For a very readable (if somewhat dated) presentation of the fundamentals of SDR receivers, see the presentation by Bob, G8VOI..

Block Diagram

This receiver implements a quadrature sampling detector to produce low frequency I and Q signals for input to the stereo line in inputs of a PC sound card. The I and Q signals are the product of the quadrature sampling detector (QSD) stage, in which bandpass filtered "chunks" of RF are mixed with quadrature clock signals to produce the down-converted I and Q signals. These products (the I and Q pairs) are identical to each other in all respects except phase, where they are 90 degrees apart.

The I/Q products of the QSD ("mixer"), when input to the appropriate SDR program through the PC's STEREO line-in soundcard input, result in a spectrum display on the PC which will show signals arrayed around a "center frequency". This "center frequency" is the frequency of the I/Q outputs from the Quadrature Clock Generators. The bandwidth of the signals either side of the center frequency will be approximately equal to the sampling rate of the PC's sound card. Thus, if the local oscillator is tuned to produce 28.4 MHz to the Quadrature Clock Generators, they will output two signals (I and Q clocks) at 7.1MHz (the "center frequency"). If the PC's sound card has a 48 kHz sampling rate, then the SDR program can translate the QSD's I/Q outputs into a chunk of spectrum that is 24 kHz either side of the center frequency of 7.1 MHz: i.e, 7.076 - 7.124 MHz.

As the user tunes the receiver, varying the frequency of the local oscillator, the micro-controller tracks the frequency and switches the appropriate bandpass filter into the RF chain. The SDR program's display will update to show the new center frequency and adjust the scale to reflect the current +/- bandwidth around that center frequency. At all times, the operator can see all signals that are within this movable "window" (whose total width is 48, 96, or 192 kHz, depending upon the sampling rate of the PC's soundcard).

The receiver is controlled via a USB connection from the PC. This USB connection provides a "USB 5V" bus for the local oscillator and micro-controller. A separate 3.3 V voltage regulator on the 5 USB 5 volt bus provides power to the programmable oscillator, the Si570.

The RX has an Atmel ATTiny85 micro-controller unit which, acting as a USB device, and on the "USB 5V" rail, controls the frequency output of the programmable local oscillator (Si570) and provides two switching signals which can be used to select one of four filter banks in the band pass filter

The output of the local oscillator is at a frequency which is 4 times the desired center frequency of the receiver and is consumed in the Quadrature Clock Generators.

The Quadrature Clock Generators divides the local oscillator frequency by 4 to produce two clock signals - QSE Clk 0 and QSE Clk 1 - which will be used to clock the QSD stage. These I and Q clock signals are identical in all respects but phase (they are in quadrature - 90 degrees phase separation).

Rf at the antenna jack is filtered through the Bandpass Filter Stage, where one of four "chunks" of the HF band is selected by the micro-controller, based upon the tuning of the programmable Local Oscillator. The filtered RF is passed as input to the QSD Stage.

The Quadrature Sampling Detector (QSD) Stage acts very similar to a mixer. It incorporates a high-speed switch that is clocked by the two QSD clock signals from the Quadrature Clock Generators and switches the incoming RF into a RC sampling network. The result is two outputs at low frequency and also in quadrature, which are the down-converted, baseband analogs of the incoming RF signals.

The outputs of the QSD stage are then fed into a pair of high gain Operational Amplifiers to produce the I and Q baseband signals which will be input to the PC soundcard's stereo Line In.

(go directly to build notes)

Ensemble RX Home 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)

Ensemble RX Home Bill of Materials

See Project Bill of Materials

Ensemble RX Home Expert's (terse) Build Notes

• Review schematics: sheet1 and sheet 2
• Build USB Side
• Build Auto BPFs
• Build QSD Clocks, Mixers, and OpAmps
• Operate Radio

Board Top

Board Bottom

(Note: 0.1 uF SMT caps are mounted to the WHITE pads; 0.01 uF caps mount to YELLOW cap pads - do not conuse these with the yellow identification of the "1" pins for the ICs.)

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 USB Power Supply Stage
• Build and Test the Local Oscillator and Control Stage
• Build and Test the Quadrature Clock Generator Stage
• Build and Test the Auto Band Pass Filters Stage
• Build and Test the Quadrature Sampling Detector Stage
• Build and Test the Operational Amplifiers 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 deciphering the winding specifications, core specifications,and construction of 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) (See BGMicro for Spare Tips)
  • 
    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.

Ensemble RX Home Completed Stage

Top of the Board

Bottom of the Board

Ensemble RX Home 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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