Local Oscillator/Control Introduction


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

The microcontroller implements a USB device which can control frequency of the programmable oscillator (Si570). Depending upon the VHF band selected (6m, 4m, or 2m) the frequency provided will be determined by a special, band-specific multiplier in the microprocessor. Refer to the Theory Section of the Home page for details on the process of generating the appropriate frequency.

The signal output from this stage will be consumed by two other stages:

(go directly to build notes)

Local Oscillator/Control Schematic

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

Local Oscillator/Controlschematic

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

(go directly to build notes)

Local Oscillator/Control Bill of Materials

Stage Bill of Materials

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

magwire30_8inMagnetic Wire, enameled #30Magnetic  Local Oscillator/Control
SO18 pin dip socketSocket  Local Oscillator/Control
T012T Bifilar #30 (4") on BN-43-2402 Xfrmr  Local Oscillator/Control
T01-coreBN-43-2402 (no markings!)none noneBinocular core  Local Oscillator/Control
U03Si570 Programmable OscillatorSiLabs 570 SiLabs 570I2C  Local Oscillator/Control
C030.01 uF103 103Ceramic  Local Oscillator/Control
C040.01 uF103 103Ceramic  Local Oscillator/Control
C300.1 uF(smt) black stripe (smt) black stripeSMT 1206  Local Oscillator/Control
C330.1 uF(smt) black stripe (smt) black stripeSMT 1206  Local Oscillator/Control
C340.1 uF(smt) black stripe (smt) black stripeSMT 1206  Local Oscillator/Control
C350.1 uF(smt) black stripe (smt) black stripeSMT 1206  Local Oscillator/Control
U04LTV-817 Opto-IsolatorLTV 817 LTV 817DIP-4  Local Oscillator/Control
U01ATtiny 85-20 PU w/V15.12 FirmwareAVR ATTINY85-20PU AVR ATTINY85-20PUDIP 8  Local Oscillator/Control
R0168 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6W  Local Oscillator/Control
R0268 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6W  Local Oscillator/Control
R032.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W  Local Oscillator/Control
R052.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W  Local Oscillator/Control
R062.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W  Local Oscillator/Control
R072.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W  Local Oscillator/Control
R082.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W  Local Oscillator/Control
R282.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W Not needed if ABPF is enabled in CFGSR for U1Local Oscillator/Control
R041 M 1/6W 5%brn-blk-grn-gld brn-blk-grn-gld1/6W  Local Oscillator/Control
D01BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial  Local Oscillator/Control
D02BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial  Local Oscillator/Control

Local Oscillator/Control Summary Build Notes

Local Oscillator/Control Detailed Build Notes

Bottom of the Board

Local Oscillator/Control Bottom View

Install Protective Topside Parts

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

Install Protective Topside Parts photo
R062.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 
R072.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 

Install Si570 Programmable Oscillator

Tin the eight pads for the si570

Align the Si570 as shown in the graphic below and solder the 1 pin. Verify that alignment is still good (adjusting and resoldering pin 1 until it is) and then solder the remaining seven pins.

Carefully examine the soldering under bright light and magnification. Most builders' Si570 problems can be traced to soldering defects, especially on the two end poins (pins 7 and 8) or to soldering in incorrect orientation

Install Si570 Programmable Oscillator photo
U03Si570 Programmable OscillatorSiLabs 570 SiLabs 570I2C 

Install SMT Caps

Solder the four SMT Caps - all 0.1 uF

Install SMT Caps photo
C300.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C330.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C340.1 uF(smt) black stripe (smt) black stripeSMT 1206 
C350.1 uF(smt) black stripe (smt) black stripeSMT 1206 

Top of the Board

Local Oscillator/Control Top View

Wind and Install T1 and Associated Components

You should take two 5" strands of #30 wire and twist them together ("bifilar") so you get around 3 twists to the inch. Using the resultant bifilar strand, thread it through the binocular core for two turns. Remember a turn is a trip that:

  1. starts at a particular hole
  2. goes into that hole and out of the other end
  3. goes into the hole nthat is across from the hole out of which it just exited, and
  4. Comes out of the hole at the opposite end and across from the original entry hole.

Do that series twice with the twisted pair and you have a transformer with two windings (each winding corresponding to one of the two twisted single wires). Each winding (primary and secondary) is two turns. Since the windings are identical in length and number of turns, you can arbitratily pick either one as the primary, with the remaining winding serving as the secondary winding.

(Hint: use an ohmmeter (or other continuity checker) to identify which wire-ends go together to make the ends of a winding.

The board layout error on the 6m/4m/2m RX Ensemble board where either the primary or secondary leads of T1 needed to be crossed for best performance has now been corrected with the latest 6m/4m/2m RX Ensemble circuit board. The new circuit board, now supplied in 6m/4m/2m RX Ensemble kits, has the date 9/8/12 in the silkscreen printing on the top surface of the board.

Wind and Install T1 and Associated Components photo
magwire30_8inMagnetic Wire, enameled #30Magnetic 
T012T Bifilar #30 (4") on BN-43-2402 Xfrmr 
C030.01 uF103 103Ceramic 
C040.01 uF103 103Ceramic 
R082.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 

Install Remaining Resistors and Zener Diodes

R28 is only needed if you disable ABPF and choose the option to have PTT control of the Quadrature Sampling Detector's enabling. We have chosen to NOT implement that capability in this documentation.

Install Remaining Resistors and Zener Diodes photo
R0168 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6W 
R0268 1/6W 5%bl-gry-blk-gld bl-gry-blk-gld1/6W 
R032.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 
R052.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 
R282.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 
Not needed if ABPF is enabled in CFGSR for U1
R041 M 1/6W 5%brn-blk-grn-gld brn-blk-grn-gld1/6W 
D01BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial 
D02BZX55C3V3 3.3V zener diodeBZX55C BZX55CAxial 

Install U1 Socket

Install U1 Socket photo
SO18 pin dip socketSocket 

Install U4 and Plug in U1

Some builders may opt to use a socket (not provided in the kit) for mounting U4, although it is not required. If you install U4 without a socket, double check the orientation, as removal post-soldering is not fun!

U04LTV-817 Opto-IsolatorLTV 817 LTV 817DIP-4 
U01ATtiny 85-20 PU w/V15.12 FirmwareAVR ATTINY85-20PU AVR ATTINY85-20PUDIP 8 

Local Oscillator/Control Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Local Oscillator/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_______

Continuity Test T1 Windings

Test Setup

Using an ohmmeter, check for continuity between the right-hand pad for C35 (point marked "A" - junction of C35 and T1-Primary winding) and the USB ground plane (point marked "B" - where C1 goes to USB ground plane). 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" - where pin 3 of U4 goes to the regular circuit ground). You should NOT get continuity; if you do get continuity, then you have a short in the windings or you have your windings crossed.

These testpoints are indicated on the schematic diagram at the top of this page and are identified so as to allow testing for continuity through the soldered joints of the coil winding.

Continuity Test T1 Windings

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Point "A" to Point "B"continuityYESyes_______
Point "A" to Point "C"continuityNOno_______

LO Output

Test Setup

Here we want to measure the output (4x center frequency for dividers). It is measured WRT (regular) ground (at the R8 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:

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

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 R8.

Below is an example of tuning the Si570 in CFGSR, selecting a center frerquency of 1.53 MHz (with an Si570 output frequency of 4x, or 6.12MHz. (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.)

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."


Frequency Will Not Change
Si570 Soldering

If the Si570 is putting out its default frequency, but does not respond to commands to shange the frequency, the most likely culprit is the soldering of pins 7 and 8 (on the long ends of the chip. Double check the soldering.

LO Output
USB Power Supply Quadrature Clock Generator RF Front End Quadrature Sampling Detector USB Cable/Plug To/From PC