I Didn't Build This!
Builder beware! These build notes are based upon the author's experiences with predecessor kits, rather than being based upon the author's build (NOT!) of the actual Ensemble RX VHF kit. Thus, there are no photos of the "completed" board, usually found at the end of each stage. In addition, many of the test results are theoretical, not supported by actual measurements on the actual kit abuilding.
I didn't do the photos, Either!
Many thanks and kudos to Nils Brolund for the fine photography on the completed kit.
This kit, based upon a design by Jan G0BBL, and implemented and distributed by Tony KB9YIG, extends the Ensemble II RX kit , replacing the front-end with a circuit that down-converts VHF signals in the 2m, 4m or 6m bands to HF signals that can be received in the RX's "back-end" (which is essentially the Ensemble II RX).
The parts provided in this kit permit the builder to select which of the major VHF bands to implement; all the parts for all the options are included in the kit. Band-specific parts are identified throughout the documentation; the builder makes his/her choice at build-time.
Relationship to the Ensemble RX II HF/LF Kit
This kit reuses a large percentage of the design of the Ensemble II RX (HF/LF) kit. Refer to that kit's home page for a theory discussion on the radio. This kit reuses the following stages, basically untouched, from the Ensemble II RX:
- Power Supply
- USB Power Supply
- Local Oscillator and Control
- Quadrature Clock Generator
- Quadrature Sampling Detector
- Operational Amplifiers
The main difference is in the RF and COntrol stage, which is based upon an earlier design for a VHF add-on board for the Softrock V9.0 RX. The theory of the Software Designed Radio can be gleaned from the Ensemble II RX documentation. Here, we will concentrate on the differences (where the RF/Auto BPF functionality is replaced with the stage described in the following paragraphs.
This discussion will use, as an example, a 144 MHZ signal that will be down-converted to an IF in the apporpriate HF frequency range for detection in the "standard SDR" stages.
The incoming signal from the Antenna terminal (or, via a jumper wire from J1/P100 Pin 1) , e.g., 144MHz, is filtered, then pre-amplified by Q1 and fed to a double-balanced mixer, U7.
U7 also receives a Local Oscillator signal via from the Si570's (U3's) LO Out. This local oscillator signal must be at a frequency (in our example, 115.2 MHz) which, when mixed with the incoming 144 MHz signal, will produce both a difference (144 - 115.2 = 28.8MHz) and the sum (144 + 115.2MHz = 259.2MHz). Fred PE0FKO's Firmware handles this translation. See notes below on how to program the AVR (U1) to result in an IF frequency that is equal to the Ensemble's quadrature clock frequency.
Intermediate Frequency (IF)
The output of the mixer at U7's pin 2 is filtered to remove the sum (image frequency). The (difference) IF is transformed into two anti-phase signals by T2 and fed to the Ensemble's Quadrature Sampling Detector via T2's secondaries and the coupling resistors R16 and R17. At this point, the radio operates pretty much the same way that the HF/LF versions of the Ensemble II RX operate.
Tuning the band is then done in the Ensemble VHF RX on signals centering around the quadrature clock frequency (converted in software to the corresponding VHF frequency display values).
Calculating the LO Frequencies
Care must be taken to calculate the LO frequencies so as to arrive at an IF that is exactly equal to the quadrature clock frequency. This is done using a multiplier factor that is specific to the band. This multiplier for 2m is 0.8; for 4m and 6m it is (4/3).
Calculation of LO frequency for 2m band
To determine the correct frequency for the SI570 for the 2m band, multiply the Desired VHF frequency by 0.8 - see following table:
|VHF||LO=0.8*VHF||Quad = LO/4||IF=VHF-(4*quad)||Shortcut = 0.2*VHF|
Calculation of LO frequency for 6m band
To determine the correct frequency for the SI570 for the 6m band, multiply the Desired VHF frequency by (4/3)- see following table:
|VHF||LO=(4/3)*VHF||Quad = LO/4||IF = VHF - (4*quad)||Shortcut = (1/3)*VHF|
Calculation of LO frequency for (EU) 4m band
To determine the correct frequency for the SI570 for the (EU) 4m band, multiply the Desired VHF frequency by (4/3)- see following table:
|VHF||LO=(4/3)*VHF||Quad = LO/4||IF = VHF - (4*quad)||Shortcut = (1/3)*VHF|
For the bands below 2m (i.e., 6m and, in the EU, 4m) the LO frequency will be higher than the desired VHF frequency. This calls for swapping the I and Q leads from their normal ring/tip orientation (this can be done by appropriately installing the jumper wires in the operational amplifier stage.(go directly to build notes)
(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 MaterialsSee Project Bill of Materials
Project Expert's (terse) Build Notes
Latest schematic sheets are at:
- Stuff all the parts
- test it all
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/Control Stage
- Build and Test the Quadrature Clock Generator Stage
- Build and Test the RF Front End Stage
- Build and Test the Quadrature Sampling Detector Stage
- Build and Test the Operational Amplifiers Stage
- Build and Test the External Connections Stage
- Build and Test the Software Setup 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 deciphering the winding specifications, core specifications,and construction of 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:
Haakko 936 ESD Solder Station (under $100)
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)