Arrl Cmos Oscillator Receiver Testing

The MTG1 Multitone Test Generator

A clean multitone signal generator is needed to test home-brew equipment. Heres one that's easy to build.

by Detlef Rohde, DL7IY

Described here is a test generator that is useful for checking the performance of short-wave transmitters and receivers. It consists of the TTG1, an audio frequency two-tone generator that was presented in the German Amateur Radio magazine cq-DL.1 This device is useful for linearity measurements of SSB transmitters and amplifiers.

The MTG1 adds an RF two-tone signal that is necessary for testing of a receiver's large-signal capabilities. Also included in the same box is a device called a "needle-pulse generator" that delivers a comb of constant amplitude marks (-73 to -67 dBm) spaced 50 or 100 kHz apart. This part of the MTG1 is useful for receiver testing and other measurements. With

'Notes appear on page 6.

Titiseestrasse 12 D13469 Berlin Germany

Crystal Stabilized Transmitter

modern components, a very compact assembly of the unit is possible as shown in the photo. Fig 1 shows the circuit diagram.

Mode of Operation

The MTG1 contains three independent crystal-stabilized oscillators from which the output signals are derived and sent to three separate jacks.

The audio frequencies, F1 and F2, are derived from a reference oscillator operating at 14.24 MHz. As in the TTG1, low-pass filtering of two square-wave signals provides a two-tone sine-wave signal with very low distortion. A very simple CMOS oscillator chip with binary dividers (4060) generates a clock signal at 222.5 kHz for the switched-capacitor filter, a

MAX293 from Maxim. The 3-dB corner frequency of the low-pass is set by this clock signal to 2.225 kHz. Square-wave frequencies of 1.738 kHz (F2) and 13.9 kHz are available on pin 2 and pin 13 of the oscillator chip, respectively.

To get two non-harmonic output frequencies which fit into the window of an SSB-filter, the 13.9-kHz wave is

Dl7iy Rohde
0 DL7IY 07/94

L1.L3 : 3 pH, 22 turns on Amidon T50-2 #22 enameled wire L2 ; 3,5 (jH, 24 turns on Amidon T50-2 #22 enameled wire

Fig 1

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