PA3ANG – Dutch Ham Radio Station – Homepage & Weblog

!! WE HAVE GOT THE CONTENT OF THE EPROM ON FILE. SEE BOTTOM OF THE PAGE !!

NOTE: I DO NOT HAVE READY TO BUILD KITS, PCBS OR EPROMS AVAILABLE. THIS PAGE JUST SHOWS HOW YOU CAN BUILD SUCH A RECEIVER. THIS PROJECT WAS 15 YEARS AGO!

Introduction

Listening to airplanes is and has always been a fascinating hobby. To do so, you need a good receiver. I decided to design and build a high performance and dedicated VHF-AM receiver. (we are talking 1994)

When I was working as a professional engineer at one of the biggest telecom companies in the world, I had the opportunity to design an build several synthesised receivers covering 118 to 136 MHz with an AM de-modulation method. Using the possibility to measure the design with high standard equipment and playing with several VCO and PLL circuitry, I ended up in with this design of a high performance AM receiver with an excellent dynamic range needed for ‘near by’ operations (listening at the field) and outstanding sensitivity to receive far away ground stations. (when listening at home)

Design

The receiver is build around a TDA 1072 AM Receiver Circuit and the used frequency synthesiser is a NJ8820 CMOS Controller. All components are general available on the market. The design is from 1994 and has not been taken further in designing a PCB or Kit to reproduce.

Click on the image to enlarge

The conserve power, during portable operations, this receiver has no digital display. In stead ‘avaialble’ BCD switches are used. Thes switches act as adress lines for the EPROM. During switching (or actually some milliseconds after the adress is stable) the corresponding data is latched into the PLL. Thereafter the EPROM circuitry is switched again to conserve power and to lower the risk of internal interference with the RF circuitry.

3235 means that the receiver is tuned to 132.350 MHz

The EPROM does contain also 80 adresses with preset frequencies. In that case the first and last digit are 0 (zero).
Furtermore, only 0, 2, 5 and 7 are valid for the 4th digit as they represent 00, 25, 50 and 75 kHz.
For example: ‘0340‘ means memory channel 34 and ‘1832‘ stands for 118.325 Mhz.

Hereunder you find the list with memory channels as they are programmed into the EPROM and valid in 1994.

Note that some of the programmed frequency are changed or no longer in use.