Design background
The JUMA-RX1 receiver was
designed for a RX-design competition announced by SRAL (The Finnish Amateur
Radio League). The task was to design and build a receiver which is suitable
for construction by a novice radio hobbyist, and which, due to its relative
simplicity, is as educational and useful as possible. The rules of the
competition were published in Nov, 2004 issue of Radioamatoori.
General
The JUMA-RX1 receiver designed
and built is based on the principle of Direct Conversion. The local oscillator
(VFO) has been implemented by a microcontroller-driven DDS (Direct Digital
Synthesizer). This facilitated compact and simple construction resulting
in excellent frequency stability and general coverage reception between
100 kHz…7.1 MHz. JUMA-RX1 is basically a DSB-type (Double-SideBand) receiver
suited for SSB and CW reception. Current consumption of the receiver is
less than 50 mA.
| Mechanical
construction
The case (Fig. 1 and Fig. 2) is made of a small (142 x 42 x 72 mm) commercial aluminum box consisting of a chassis and its cover. The holes for display, controls and connectors have been drilled (and sawed) to the front and rear panels of the chassis. There’s a small loudspeaker below the cover. |
 Figure 1. JUMA-RX1 front view |
 Figure 2. JUMA-RX1 rear view |
| The
building blocks of the receiver
There are two printed-circuit boards in the receiver, the RX-main board and the DDS-control board. The display is a ready-made LCD-module (Figure 3). The RX-main board contains the mixer, necessary amplifiers, SSB-filter, AGC, and voltage regulation. The RX-main board provides the DDS board with S-meter voltage and 12 V supply voltage. Local oscillator signal is generated by the DDS board. The DDS board incorporates
a digital local oscillator driven by an on-board microcontroller. Frequency
is adjusted by a rotary encoder read by the micro-controller which then
sets the DDS frequency. In addition, the on-board microcontroller drives
the LCD display indicating frequency and bar-type S-meter readings or supply
voltage. The microcontroller also generates acknowledgement audio tones.
|
 Figure 3. JUMA-RX1 construction |
Happy home brewing!
73 de Juha OH2NLT and Matti
OH7SV