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RECEIVE CONVERTER FOR 630M BAND

630m band (472kHz-479kHz) Receive Converter. Under development


The receive converter consists of tree main elements, Low Pass Filter to mitigate strong AM broadcast band transmission over loading the receiver, a single transistor amplifier and Ring Mixer to step the 630m band (472kHz-479kHz) signals up to the 30m band frequency range of 10.472MHz-10.479MHz. While 472kHz-479kHz is the range of interest for this project the receiver converter is well capable good reception well below these frequencies.  

 

Fig 1 Schematic of the receive converter. This circuit is subject to further development.

 

Component details

TUF-1+ Frequency Mixers Module
Q1 Transistor - 2N3904 or 2SC2671 TO-92
Q2 Transistor - 2N3904 or 2SC2671 TO-92
R1 Resistor 1k 0.25W Carbon
R2 Resistor 1k 0.25W Carbon
R3 Resistor 100R  0.25W Carbon
R4 Resistor 470R  0.25W Carbon
R5 Resistor 10k  0.25W Carbon
R6 Resistor 680R  0.25W Carbon
C1 Capacitor - Ceramic - 220nf
C2 Capacitor - Ceramic - 15nf
C3 Capacitor - Ceramic - 20nf
C4 Capacitor - Ceramic - 20nf
C5 Capacitor - Ceramic - 15nf
C6 Capacitor - Ceramic - 100nf
C7 Capacitor - Ceramic - 22nf
C8 Capacitor - Ceramic - 50pf
C9 Capacitor - Ceramic - 22nf
L1 14.7uH = 10uH + 4.7uH Epoxy Dipped RF Radial Choke
L2 22uH Epoxy Dipped RF Radial Choke
L3 14.7uH = 10uH + 4.7uH Epoxy Dipped RF Radial Choke

 

 

Photo 1 Assembled receive converter.

 

Photo 1 Assembled receive converter.

 

Low Pass Filter 

 

With the 630 metre band being so close to the AM broadcast band it necessary to provide a low pass filter to attenuate potentially strong signals that may desensitise the receiver. AADE Filter Design 4.5 was used to design and analyse the receiver's low pass filter stage. 

Fig 2 AADE Filter Design 4.5 attenuation analysis of the receiver low pass filter circuit.

 Fig 2 AADE Filter Design 4.5 attenuation analysis of the receiver low pass filter circuit. 

The real world filter circuit assembly was testing and exhibited an attenuation curve approximately 25kHz higher in frequency as compared to the model. See Fig 3. The higher cut off frequency of the low pass filter was surprisingly high as the AADE Filter Design 4.5 application had generally provided fairly accurate modelling of similar filters, however the resulting low pass filter performance is sufficient for the proposed receive converter. The variation in modelling when compared with the physical circuit performance may be a result of the use of the cheaper Epoxy Dipped RF Radial Chokes.

Fig 3 Low Pass Filter attenuation measurements graphed with excel. 

Fig 3 Low Pass Filter attenuation measurements graphed with excel. 

 

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Page last revised 05 May, 2015  
 

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