VHF Airband Receiver

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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.
Note: we are talking 1994!!
Note: I do not have ready to build kits, pcb’s or Eproms available. This page just shows how you can build such a receiver. This project was more then 25 years ago.

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 used in the Netherlands in 1994.

Specifications

Frequency range 118 – 136 Mhz
Channel steps 25 KHz
Memories in EPROM (fixed)
Mode A3
Circuit type Double Conversion
Intermediate freq. 21.4 MHz and 455 KHz
Sensitivity 1uV @ 10dB S/N
Squelch sensitivity .7uV
Selectivity(-6/-60dB) 6 KHz/20KHz
Image Rejection 40 dB
Supply Voltage 13.8 Volt (9.0 – 16.0 V)
Accu NiCad 8x AAA Cells
Current Consumption 250mA (Approx.)
Size (w,h,d) 100 x 43 x 130 mm
Housing Metal
Antenna receptor BNC

The circuitry is build on a versatile PCB used for experimenting with RF grounding grid toplayer. The antenna is a VHF helical and the casing a modified ‘everywhere’ to buy casing. (I made it a little smaller)
The 8 ‘AAA’ NiCad cells are underneath the PCB. The EEPROM holds the data for the PLL and is controlled by the BCD switches.

To finish off the description a last picture of the receiver detailing out the frontpanel connections and components build up.

Block Diagram

As already outlined, I have never brought the design to maturity and to transform it into a re-buildable design or kit. Nevertheless you are free off course to use the design and create yours. The block diagram and schematics can help you in choosing the right components.

Band-pass filter
HF Amplifier
Mixer SCM1 or SBL1 type
MF Amplifier 21.4 MHz
MF stage 455 KHz and De-modulation
Squelch circuit
LF amplifier
VCO, Synthesiser and LPF
ROM and BCD switches
Power supply

Schematics

Download the complete schematic by clicking here.

EPROM content

We finally found a partner to read and copy the content of the EPROM. The 27512 EPROM contains the devider setting for the PLL. The data is now available in HEX or Motorola S1F format.
You can download it by clicking one of the links: hex  s1f

Future

Flying this airplane?

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