AM Receiver - From 0 Hz up to 1.8 Mhz

 

Introduction

Frequency Table

Block Scheme

Electrical Scheme

Part List

PCB Layout

PCB

PCB Fully Assembled

How to adjust and use

 

 

 

A short introduction



This radio receiver can tune stations since 0 Hz up to 1,8 Mhz, quite uncommon situation because any normal AM receiver is only able to receive to long wave radio stations (150 to 433 Khz) and medium waves (520 to 1612 Khz).

Will this widening of the reception band be useful to anyone ? For those who live near the maritime coast, will be able to appreciate the reception in the band of 1600 the 1800 Khz where the naval stations work and get useful information, mainly the weather forecast.

The activity in such low bands (VLF 9 to 148.5 Khz) includes the comms with submarines, RTTY stations, the famous time clock signs of great accuracy, such as station DCF77 (77.5 Khz) and beautiful Earth's natural sounds like sferics, tweeks and wishtlers. (For more information about these sounds check The Natural Radio Home Page, in this site).

 

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Frequency Table

Frequency in Khz Callsign Service
18.3 UNID RTTY
53.6 RTO Moscow Meteo
60.0 MSF Rugby TS - Time Clock
75.0 HBG Nyon TS - Time Clock
77.5 DCF77 Mainflingen TS - Time Clock
82.8 MKL Royal Air Force- Edinburgh
111.3 SOA211 Varsovia - Meteo
117.4 DCF37 Offenbach Meteo
129.1 DCF49 BMPT Bonn
139.0 TBA TN Ankara
147.3 DDH47 Hamburg Meteo

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Block Scheme

 

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Electrical Scheme

 

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Part List

R C L Semicondutors Misc.
R1=1MOhm C1/C23/C35 = 10 pF L1=3.9uH D1=MV1401 (Motorola) LS1= Speaker 8 Ohm -1W
R2/R3=100 KOhm C2/C3/C5/C11/C17/C18/C21
/C24/C26/C27/C33/C36/C44/= 100 nF
L2/L3= 100 mH D2=1N4001 X1- Ceramic Filter10.7 Mhz (10M7A)
R4=1 KOhm C4/C9/C10/C28/C29=220 nF L4=1.5 uH D3= LED X2= Ceramic Filter SFR455H
R5=820 Ohm C6/C8=56 pF L5=680 uH T1=BF961 X3=Quartz Cristal 10.245 Mhz
R6=1.8 KOhm C7=180 pF L6=82uH T2=BF494 P1=Multiple Turn 50 KOhm
R7=150KOhm C12=22pF L7=12 uH T3=BC550C  
R8=3.9 KOhm C13=33pF   T4=J310  
R9=1.2 KOhm C14/C16/C43=100pF   IC1=SA612AN (Philips)  
R10=2.7 KOhm C15 = Adjust. 40 pF   IC2=TDA1572  
R11=330 KOhm C19/C20/C41=10 nF   IC3=LM386N  
R12=100 Ohm C22=120 pF   IC4=78L09  
R13=22Ohm C25=47 uF-16 V   IC5=78L06  
R14=1 Ohm C30=2.2uF - 16 V      
R16=10 KOhm C31/C34= 22uF - 16 V      
R17=820 KOhm C32=3.3 nF      
R18/R20=2.2 KOhm C37/C38=220 uF - 16 V      
R19=220KOhm C39/C40=10uF - 63 V      
  C42=39pF      

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PCB Layout

 

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PCB

 

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PCB Fully Assembled

 

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How to adjust and use

 

The calibration is made by the adjustment of C4 to define the local oscillator's frequency gamma. To make this adjustment, temporarily short circuit between the input of the antenna and the ground, binding a wire from the point A and ground. After that, turn P1 in the anti-clockwise direction. Slowly turn C15 from the central position until hearing a sign. You can use also a frequency meter between PINs 6 and 7 of IC1 and adjust C15 until read 10.7 Mhz.

The disadvantage of this way is that the load of the circuit by the measure device, can cause a certain frequency oscillation. To prevent this problem, connect a resistor with 10 KOhm between pin 1 and ground. In this situation, we will have the same frequency generated by the local oscillator and could easily be measured with one frequency meter or oscilloscope.

Finally remove the 10 KOhm resistor and the short circuit in A and connect a vertical antenna in that point. The antenna can be build by an isolated wire. The ideal wire size is between 10 and 20 centimeters. Bigger antennas will magnify the reception of atmospheric noise.

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10-06-2001