Elecraft 2T-Gen User Manual

ELECRAFT 2T-gen 2-Tone TEST OSCILLATOR

Rev B, March 10, 2010

Introduction

The Elecraft 2T-gen is a 2-Tone test oscillator that can be used to make distortion measurements on SSB
transmitters and amplifiers. The 2T-gen is battery operated and provides sufficient output level to be
connected directly to the microphone connector of almost any transceiver.

Specifications

AF Output Level 200 mV max, adjustable, female RCA connector
Frequency 700 Hz and 1900 Hz
Harmonic Distortion -55 dB typical
Current Drain About 3mA from on-board 9-V battery
Size PC board: 3.5"L x 2.4"W; 1.0"H

Parts Inventory

R2,R6 (2) Res, 8.25 k 1% (gry, red, grn, brn, brn), E500176
R3,R9 (2) Res, 3.3k 5% (org,org,red), E500017
R5,R11 (2) Res, 1M 5% (brn,blk,grn), E500024
R4,R10 (2) Res, 100k 5% (brn,blk,yel), E500006
R1, R7 (2) Res, 6.8k 5% (blu,gray,red), E500115
R8,R12 (2) Res, 22.6k 1% ( red, red, blu, red, brn), E500175
R13, R14 (2) Res, 10 k 5% (brn, blk, org), E500015
R15,R16,R17,R18 (4) Res, 22K 5%, (red,red,org), E500090
R20 (1) Res., 47K 5% (yel,vio,org), E500067
C1, C3,C5,C7 (4) Mono Cap, 0.22uF (224), E530079
C2,C4,C6,C8 (4) Poly Cap, 0.01UF (103), E530009
C9, C10 (2) Electrolytic Cap, 22 µF E530143

D1 (1) Red LED, round, E570025
R19,R21 (2) 10k Pot, E520005
S1 (1) Miniature slide switch, E640009
JP1, JP2 (2) 3-pin header, E620053
J1 (1) RCA Connector, E620057
U1, U2 (2) LMC6842AIN, E600011
Q1,Q3 (2) Transistor, 2N3904, E580017
Q2,Q4 (2) Transistor, 2N7000, E580002

(1) 2T-gen Printed Circuit Board, E100256
(4) Self-adhesive mounting feet, E700024
(2) 2-pin jumper block, E620055
(2) 4-40x5/16 machine screws, E700077
(2) #4 internal tooth lockwashers, E700010
(2) 4-40 machine nuts, E700011
(1) Battery Holder, E980074

1

Assembly

 Sort the resistors by value. Some of the color bands may be hard to read; use a magnifying glass if necessary. A

Digital Multimeter (DMM) should be used to confirm the values.

 Orient the printed circuit board with the silk-screened side up and the title “2T-gen” at the upper left.
 Install the following resistors in their indicated positions, starting at the top of the PC board and working down

and right. (Complete the left column, below, then the right column.)

__ R10, 100k, 5% (brn,blk,yel)
__ R16, 22k, 5% (red,red,org)
__ R11, 1M, 5% (brn,blk, grn)

__ R8, 22.6k, 1% (red, red, blu, red, brn)

__ R7, 6.8k, 5% (blu,gry,red)
__ R9, 3.3k,5% (org,org,red)
__ R12, 22.6k, 1% (red, red, blu, red, brn)
__ R15, 22k, 5% (red,red,org)
__ R14, 10 k, 5% (brn, blk, org)
__ R17, 22k, 5% (red,red,org)

__ R5, 1M, 5% (brn,blk, grn)
__ R18, 22 k, 5% (red,red,org)
__ R13, 10 k, 5% (brn, blk, org)
__ R2, 8.25k, 1% (gry,red,grn,brn,brn)
__ R1, 6.8k, 5% (blu,gry,red)
__ R3, 3.3k,5% (org,org,red)
__ R6, 8.25k, 1% (gry,red,grn,brn,brn)
__ R20, 47 k, 5% yel,vio, org)
__ R4, 100k, 5% (brn,blk,yel)

 Install the mono ceramic capacitors listed below:

__ C7, .22µF (224) __ C5, .22µF (224) __ C3, .22µF (224) __ C1, .22µF( 224)

 Install the poly capacitors listed below:

__ C6, .01µF (103) __ C8, .01µF (103) __ C2, .01µF (103) __ C4, .01µF (103)

 Install the electrolytic capacitors listed below, Insert the long lead into the square pad.

__ C10, 22uF 25 V __C9, 22uF 25 V

 Install the Red LED at D1. Insert the long lead into the square pad.
 Install R19, a 10k (103) pot, on the left edge of the board as shown by its outline.
 Install R21, a 10k (103) pot, on the left edge of the board as shown by its outline.
 Install J1, the RCA connector, on the left edge of the board as shown by its outline.
 Install switch S1, on the left edge of the board as shown by its outline.
 Install the headers, JP1 and JP2 near the top and bottom edge of the board.
 Install U1 and U2 in their indicated positions. Align the notch in the top of the package with the outline on the

printed circuit board.

 Install Q1, Q2, Q3, and Q4 in their indicated positions. Align the flat side of the package with the outline on the

printed circuit board.

 Install the jumper blocks on the pins marked “T” on JP1 and JP2.
 Install the battery holder at BT1. Use 4-40 hardware
 Install 4 mounting feet on the back side of the board as shown in the photo on page 7.

2

Initial Test



Set S1 (small slide switch) to the OFF position.

 Install a 9V battery into its holder.
 Connect the output of the 2T-gen to the input of a sound system or to headphones using a suitable

adapter cable.

 Set R19 and R21 to about mid-range.
 Turn on the 2T-gen. The round red LED will light.
 The 2T-gen output should be heard on the sound system or headphones.
 Place the jumper block over the “NT” pins or JP1 and JP2 in turn and confirm that only a single tone is

heard when the jumper block is in place.

 Return the jumper blocks to the “T” position.
 This completes the initial test. Turn off the 2T-gen to conserve the battery

Using the 2T-gen

Controls and indicator LEDs

 Power-on LED (red): Turns on when the 2T-gen is in use.
 Output Level Adjust: Allows adjustment of the output level to the desired level.
 Balance: Allows adjustment of the two tones to produce equal transmitter output power.
 JP1 and JP2: Provide control of the oscillators. Placing a jumper block over the “NT” pins will turn off

the associated oscillator. Placing a jumper block over the “T” pins, or removing it entirely, will turn on
the associated oscillator. JP1 controls the 700 Hz oscillator and JP2 controls the 1900 Hz oscillator.

Applications

The 2T-gen has been designed to provide a 2-tone signal source for testing of SSB transceivers and
associated amplifiers. This type of testing is almost universally used as a measure of transmitter linearity for
amateur radio equipment. Results of 2-tone IMD tests can be found in every ARRL review of new
transceivers and power amplifiers.

When connected to the 2T-gen, the ideal SSB transmitter will produce an output that consists of only two
frequencies, for USB these will be the carrier frequency plus 700 Hz and the carrier frequency plus 1900 Hz
and for LSB the frequencies will be carrier minus 700 Hz and carrier minus 1900 Hz.

Actual transmitters will produce spurious output at additional frequencies as a result of nonlinearity. The
highest amplitude spurious output will normally be the third-order product and the next highest will be the

order product. Higher-order products may also be present at lower amplitudes. These spurious products

5th
are referred to as the intermodulation distortion (IMD) products.

The 3rd order product will appear at a frequency offset from the carrier by 2F2 –F1 and the 5th order product
will be offset from the carrier frequency by 3xF2-2xF1. For the 2T-gen, F1 is 700 Hz and F2 is 1900 Hz,

3