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. 2022 Sep 8;22(18):6784.
doi: 10.3390/s22186784.

High Performance Broadcast Receiver Based on Obsolete Technology

Laurenţiu Teodorescu  1   2 , Gabriel Dima  1
Affiliations

High Performance Broadcast Receiver Based on Obsolete Technology

Laurenţiu Teodorescu et al. Sensors (Basel). .

Abstract

Since its inception, the electronics industry has mass-produced equipment. The fast evolution of electronic technologies made obsolete the entire generation of products and even technologies. Until the government issued regulations and guidelines on how to address the issue of reuse of obsolete electronic equipment, with special regard to the ones still operating (e.g., give it to family/friends, donate to charity, or sell to individuals or recycling companies), most of it was thrown out with usual rubbish, with a destructive effect on the environment. This paper presents the design techniques and methods for revaluation of obsolete vacuum tube analog receivers, with a focus on the manufacturing steps of a high-performance receiver. The choice of receiver type is not accidental at all, since tube technology is still a real success among audiophiles many providers offer vacuum tube amplifiers at considerably high prices. The redesign implied the original FM unit replacement with a DSP-based AM/FM tuner while the AM RF vacuum tube section has been preserved with the original architecture to allow the reception of the broadcast stations for the long-wave band and the alternative operation with the silicon tuner for the medium-wave and short-wave bands. The electrical performances of the modified receiver in terms of reliability, sensitivity, selectivity, and distortions on the reception chain are clearly superior to the original one, while the power consumption of the RF section is reduced more than 10 times from 11.5 W-15.5 W to 1 W. Last, but not least important, the proposed solution implied the use of few additional parts and resources and extended significantly the lifetime of the original vacuum tubes receiver. The work has been developed to serve as an example of how obsolete electronic equipment can be redesigned and reused avoiding its complete recycling or even worse, its disposal with usual rubbish. It has been imagined and performed as the initial step in launching a professional student contest on the reuse/redesign of obsolete equipment aimed at raising awareness regarding the issue of pollution with e-waste amongst students from the electronic departments of Romanian technical universities.

Keywords: digital receiver; digital signal processor; environment protection; high fidelity; obsolete analog radio; radio frequency; recycling method; vacuum tube.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The block diagram of the original vacuum tube receiver.
Figure 2
Figure 2
The proposed architecture of the broadcast receiver.
Figure 3
Figure 3
The structure of the modified audio amplifier.
Figure 4
Figure 4
The first stage of the audio amplifier.
Figure 5
Figure 5
The replacement of the multi-tap potentiometer by an equivalent circuit.
Figure 6
Figure 6
The structure of the input filter by considering the impedances of the RC filters and four discrete values for the cursor of the volume potentiometer.
Figure 7
Figure 7
The influence of the R65 (bass cut) potentiometer in the voltage transfer function of the audio preamplifier (R71, R81 have the maximum values).
Figure 8
Figure 8
The influence of the R71 (volume) potentiometer in the voltage transfer function of the audio preamplifier (R65, R81 have the maximum values).
Figure 9
Figure 9
The influence of the R81 (treble cut) potentiometer in the voltage transfer function of the audio preamplifier (R71, R65 have the maximum values).
Figure 10
Figure 10
The tone register circuit.
Figure 11
Figure 11
The frequency response of the tone register filters.
Figure 12
Figure 12
The power audio amplifier (2nd and 3rd amplifying stages).
Figure 13
Figure 13
The PA negative feedback network.
Figure 14
Figure 14
The measurements setup for the audio amplifier section of the broadcast receiver.
Figure 15
Figure 15
The amplitude–frequency characteristic of the audio amplifier for various values of R65 (bass–cut) and R81 (tone–cut) potentiometers (Stereo mode, sine wave input signal, 10 Hz ÷ 100 kHz range, 0 dBv voltage).
Figure 16
Figure 16
The block diagram of the filter board.
Figure 17
Figure 17
The frequency response introduced by the filter board used for THD measurements (input signal: sine wave, range 10 Hz–100 kHz, amplitude 0 dBv).
Figure 18
Figure 18
The block diagram for the power supply section.
Figure 19
Figure 19
The structure of the tuner section.
Figure 20
Figure 20
The measurement setup for the digital RF receiver.
Figure 21
Figure 21
The setup for noise figure measurement.
See this image and copyright information in PMC

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