tecsun: Tecsun R-9701 - Technical details

These observations are based on the "R-9701-V7" PCB with a date code of "2013.06.15" that also shows a "(2SK373)" label printed in the PCB silkscreen. This design version shows a few differences to a previous design as seen in the schematic diagram.

The antenna signal is passed thru a band pass filter (F3 in the schematic diagram, BPF88108 on the R-9701-V7 PCB).

The F3 secondary coil feeds the FM signal directly to the CD2003GP AM/FM Tuner IC RF FM input pin 1.

The F3 primary coil feeds the SW AM signals to the Front-End amplifier/1st Mixer Q11 thru a low pass filter C38, L3, C21.

The SW 1st local oscillator Q2 uses one from seven crystals (X1=16.8MHz; X2=17.9MHz; X3=20.4MHz; X4=22.5MHz; X5=24.4MHz; X6=26.05MHz; X7=28.5MHz), one per SW band.

The 1st IF output is handled by T9 and CF4 (10.7MHz) that passes the 1st IF signal to the CD2003GP IC AM RF input pin 16.

The band pass of each SW band is around 500 kHz, a common value in these kind of crystal stabilized local oscillators circuits (see the scale dial values). 

The SW 2nd local oscillator is handled by the CD2003GP IC pin 12 using T7 and variable capacitor PVC4 section, where the 2nd IF signal at 455 kHz is obtained at pin 4 and injected to pin7 thru CF5 (455 kHz) amplified by Q9 (missing in the R-9701-V7 PCB).

The AM MW signal tuned by the magnetic antenna L1 and variable capacitor PVC1 section is passed directly to the CD2003GP IC AM RF input pin 16. The MW local oscillator is handled by the CD2003GP IC at pin 12 using T8 and variable capacitor PVC4 section. The MW IF frequency is 455 kHz.

The additional transistors are used as switches to select the different RF bands.

The audio signal from CD2003GP IC is passed to the Audio Amplifier IC thru capacitive coupling C12 and volume potentiometer.

The 16 Ohm 0.25 Watt 16T57Z-2 built-in speaker is driven in BTL mode by the Audio IC.

 

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