Local Oscillator and Control Introduction


This stage completes the component installation for the isolated USB ground plane and implements the microcontroller and local oscillator functionality.

The microcontroller implements a USB device which can control frequency of the programmable oscillator (Si570) and provides programmatic band-select switching signals to select from among bands 0, 1, 2, and 3. These bands are "super bands" which, depending upon the builder's choice of options, provide coverage of the traditional HF bands or a set of HF bands plus 6m.

(go directly to build notes)

Local Oscillator and Control Schematic

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

(Click for Full Schematic)
Local Oscillator and Controlschematic

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

(go directly to build notes)

Local Oscillator and Control Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

11 M 1/6W 5%brn-blk-grn-gld brn-blk-grn-gld1/6W
210 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6W
52.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W
12.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W
268 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6W
2BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial
1BN-43-2402 (no markings!)none noneBinocular core
10.01 uF103 103Ceramic
1ATtiny 85-20 PU w/V15.12 FirmwareAVR ATTINY85-20PU AVR ATTINY85-20PUDIP 8
2LTV-817 Opto-IsolatorLTV 817 LTV 817DIP-4
1Si570 Programmable OscillatorSiLabs 570 SiLabs 570I2C
1Magnetic Wire, enameled #30Magnetic
30.1 uF(smt) black stripe (smt) black stripeSMT 1206
18 pin dip socketSocket
12T Bifilar #30 (4") on BN-43-2402 Xfrmr

Local Oscillator and Control Summary Build Notes

Local Oscillator and Control Detailed Build Notes

Bottom of the Board

Local Oscillator and Control Bottom View

Install Protective Topside Parts

Install these resistors first, so as to protet against solder splashover at pins 4 and 8 off the Si570 (see below)

Install Protective Topside Parts photo
R072.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WN-S
R082.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WN-S

Install Bottomside Components

Watch out when installing C35 to avoid solder splashover into the adjacent holes for the T1 primary windings.

Note the orientation photo for the Si570 and install with correct orientation. Pay close attention to the pins 4 and 8, as their footpring is quite small relative to the other pads.

U03Si570 Programmable OscillatorSiLabs 570 SiLabs 570I2C 
C300.1 uF(smt) black stripe (smt) black stripeSMT 1206white pads
C330.1 uF(smt) black stripe (smt) black stripeSMT 1206white pads
C350.1 uF(smt) black stripe (smt) black stripeSMT 1206white pads

Top of the Board

Local Oscillator and Control Top View

Wind and Install T1

This is a transformer, wound using a "bifilar" strand. The strand is made of a single wire, doubled over to make two wires, and twisted together to about 3-4 twists per inch. It is then threaded through the binocular core for the required number of turns (2). Once wound, the strand is cut at the bent end, yielding four leads. Then, check the leads with an ohmmeter to identify which leads are electrically connected.

Since the windings are both of identical length, the identification of the "primary" and the :secondary" windings is easy: select one winding (i.e., pair of leads that show continuity) and call it "primary"; the remaining winding is the "secondary" winding.

If you are unfamiliar with winding and installing inductors, you may want to refer to the WB5RVZ construction hints for coils (toroidal) and transformers ( toroidal and binocular). Click here for details on identifying toroid cores.

Decoding the trqansformer specifications:

Transformers' windings are specified using the pattern "nnT/wXmmT" or "wXmmT/nnT", where:

  • "nn" is the number of turns in the single winding
  • "mm" is the number of turns in the multiple windings
  • "w" = the number of multiple windings (e.g., 2 = bifilar; 3 = trifilar, etc.)

Thus, e.g., "18T/2x9T bifilar #30" means, using #30 wire, produce a single 18 turn primary winding and two 9-turn secondary windings; "2x9T bifilar/ 18T #30" means, using #30 wire, produce two 9-turn primary windings and a single 18 turn secondary winding.

magwireMagnetic Wire, enameled #30Magnetic 
(total of 30 ft. provided in kit)
T012T Bifilar #30 (4") on BN-43-2402 Xfrmr 
change from 3Ttrifilar

Install Topside Ics

Double check the orientation on the two optoisolators. They should be oriented so that their "dimple" is in the upper left-hand corner.

SO18 pin dip socketSocket 
for ATTiny85
U01ATtiny 85-20 PU w/V15.12 FirmwareAVR ATTINY85-20PU AVR ATTINY85-20PUDIP 8(dimple in upper right)
U04LTV-817 Opto-IsolatorLTV 817 LTV 817DIP-4(dimple in upper left)
U05LTV-817 Opto-IsolatorLTV 817 LTV 817DIP-4(dimple in upper left)

Install Remainder of Topside Components

Careful installing the resistors and diodes clustered near the USB connector area. Builders have been known to insert these into the wrong holes. Review the board layout and the orientation column below to double check the orientation.

The body of each zener is to be located above the silkscreen circles for D1 and D2 on the board with the diodes mounted standing perpendicular to the board in a hairpin fashion. The banded end of each diode is then at the lead of the diode that loops back to the circuit board.

D1BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial 
The band end of the diode is the hairpin lead - see board layout
D2BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial 
The band end of the diode is the hairpin lead - see board layout
C030.01 uF103 103Ceramichoriz
R0168 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6WN-S
R0268 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6WN-S
R032.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WE-W
R052.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WW-E
R062.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WW-E
R092.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WW-E
chenged from 221
R1210 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WN-S
R1310 k 1/6W 5%brn-blk-ora-gld brn-blk-ora-gld1/6WN-S
R041 M 1/6W 5%brn-blk-grn-gld brn-blk-grn-gld1/6WE-W

Download and Install Required Software

All of the latest versions of essential firmware configuration programs, USB driver and their associated documentation can be obtained from Fred PE0FKO's website:

In order to test (and later, operate) your rig, you must download and install required software (SDR programs and Dynamic Link Libraries, along with hardware drivers. The actual steps and programs may vary, depending upon your computer's windows operating system version (XP, Vista, or Windows 7) and architecture CPU/memory (32 bit or 64 bit).

The following links are provided and, as of 7/8/2010, are current:

SoftwareRole/PurposeDownload LinkNotes
CFGSRConfigure/Control Ensemble microcontrollerdownload
SRDLLdll for Softrock controllersdownload
USB driver(s)drivers for ATTiny85 USBdownloadZip file with 32 and 64 bit drivers*.
WinRadHDSimple SDR (RX only) Programdownload
(Windows XP) PowerSDR-IQ V1.12.20Version of FlexRadio's PowerSDR tailored for I/Q Soundcard-based SDRs downloadHas Si570 Control Capability
(Windows 7, Vista) PowerSDR-IQ V1.19.3.15Version of FlexRadio's PowerSDR tailored for I/Q Soundcard-based SDRs downloadHas Si570 Control Capability (Please see Christos' message 43204 on the Yahoo Reflector)

*Note on installing PE0-FKO's USB Drivers: Fred's website has an excellent step-by-step guide to instaling the USB driver.

Install Driver

The correct procedure is to download the driver and put it in a suitable folder, then plug in the USB lead, Windows should detect new hardware has been found and you need to manually point it to the folder containing the drive. It should then install correctly. Certainly does on Win2000 and XP. On Vista or Windows 7, there used to be some issues with driver signing. There have been messages on the forum describing methods of working around these issues. One such solution is addressed in the author's MOBO4.3 builders notes.

LibUSB - "Unknown Device" Error

Others have experienced the dreaded "Unknown Device" problem upon plugging in the USB cable after having installed the LibUsb driver. This "unknown device" problem (and a remedy for those who are using Logitech cordless mouse and/or various wireless internet connection adaptors) are discussed in message #45071 and Message #47755 on the Yahoo Softrock40 Group

Install/Run CFGSR ("ConFiGureSoftRock")

Once the driver is installed, if you run 'CFGSR' that will either automatically 'open' the firmware, or if not, you need to go to the 'USB' tab and select it from the list displayed in the bottom box. Which way depends on if you have 'CFGSR' set up to auto connect on program start or not.

Test Local Oscillator

You can use 'CFGSR' to exercise the Si570 using the 'Tune' tab that makes it into a 'VFO'. Just a case of setting the frequency, and the Si570 should output a signal at 4 times the frequency displayed on the main display on the screen. The 'Test' tab can also be used to look at all the various Si570 registers etc, but probably unnecessary as if you can hear or measure the Si570 output frequency, you know it is working.

Local Oscillator and Control Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Local Oscillator and Control Testing

Current Draw

Test Setup

Power up the regular circuit side of the board

Measure the current draw on the 12 V power lead (WITHOUT the USB plugged in)

Plug in the USB cable and keep 12V power to the main circuit

Measure the current draw on the 12 V power lead (WITH the USB plugged in). You should get a slightly higher current draw.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Current Draw - NO USBmA< 84.3_______
Current Draw - USB plugged inmA< 95.3_______

Test T1 Windings

Test Setup

Using an ohmmeter, check for continuity between the right-hand pad for C35 (point marked "A") and the USB ground (point marked "B"). You should get continuity (~ 0 ohms). Then, check for continuity (~ 0 ohms) between the right-hand pad of C35 (point marked "A") and the regular ground (point marked "C"). You should NOT get continuity; if you do get continuity, then you have a short in the windings or you have your windings crossed. Test T1 Windings

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
"A" to "B"ohms~0_______
"A" to "C"ohms~ infinity_______

LO Stage Outputs

Test Setup

Here we want to measure the output (4x center frequency for dividers). It is measured WRT (regular) ground (at the R9 hairpion lead).


Be sure all software and drivers, etc., have been installed. Connect the USB jack via USB cable to the PC. You should hear the "BoopBoop" sound the PC makes when it recognizes a device (the Ensemble) has been attached to a USB port..

Next, run CFGSR.exe and you should get the following screen:

CFGSR General Tab

Then, check out the "Si570" tab. It should look like this:

CFGSR Si570 tab

Note that the Local Oscillator's outputs are measured with respect to the analog ground plane, NOT with respect to the galvanically isolated USB groundplane. The /QSD EN shunt is a good point for this ground connection.

Using the CFGSR Software (at the "Tune" tab), test scenarios for setting the center frequency (remember, the Si570 produces a signal that is 4 times the desired center frequency).

Measure the output at the hairpin lead of R9.

Below is an example of tuning the Si570 in CFGSR, selecting a center frerquency of 6.05 MHz (with an Si570 output frequency of 4x, or 24.2MHz. (Pay no attention to the lousy oscilloscope behind the curtains - the output is really a square wave, but the scope is a cheap USB scope that doesn't sample HF square waves very well.)

Testing Si570 output

You can place your mouse on the frequency in the center frequency field and turn your mouse wheel. The center frequency will increase or decrease and the LO Output frequency (4x) will increase or decrease at a rate 4 times that of the center frequency.

John, KB6QL, discovered this trick for those with no scope, counter, or HF radio to use in testing LO output:

"Turns out that local oscillator can be tuned for a frequency that is in the FM band. So, as a quick and dirty, I got out my little MP3 player-cum-FM-radio and tuned it to that frequency and let the headset cord/ant drape over the RX. It gave me full quieting. Then I switched the RX to another frequency and the quieting was gone."

Trouble Shooting

If the LO oscillates at the factory default frequency but will not respond to your attempts to change the frequency, the very first place to look is on the soldering of the Si570, most especially pins 7 and 8. Those pins - and their soldering - constitute the single most often found cause of inability to change the frequency of the Si570.

LO Stage Outputs

Validate Filter Selection Outputs

Test Setup

Start up CFSR again and tune the local oscillator through four frequencies (each being in the middle of one of the bands):

  1. 2MHz
  2. 6MHz
  3. 12MHz
  4. 24MHz

Measure the voltages at "FL SEL 0" (R13 hairpin) and "FL SEL 1" (R12 hairpin) with respect to regular ground

(The high/low values at R12 and R13 are used in the ABPF switching truth table, shown in the Automatic Band Pass Filter stage's introductory paragraphs.

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
R12 (for 2 MHz band 0)Vdc0100 mV_______
R12 (for 6 MHz band 1)Vdc0100 mV_______
R12 (for 12 MHz band 2)Vdc54.92_______
R12 (for 24 MHz band 3)Vdc54.92_______
R13 (for 2 MHz band 0)Vdc0100 mV_______
R13 (for 6 MHz band 1)Vdc54.92_______
R13 (for 12 MHz band 2)Vdc0100 mV_______
R13 (for 24 MHz band 3)Vdc54.92_______
USB 5V dc to the USB Power Supply 3.3 V dc from USB Power Supply Local Oscillator Output to Quadrature Clock Generator Filter Selection Signals to Auto-Switched BPF