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[SOLVED] problem with sensitivity of SA615

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xandeyes

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hello everyone.
i have problem with sensitivity SA615.
my input frequency is 21.4MHz ( modulation 1KHz audio,lever 5.6kHz) and IF = 455KHz . the crystal OSC is 20.945 MHz

I rematching RF input, use ADS simulation and after installation, I measure with VNA , equal S11 = -15dBm ( at 21.4MHz)
the circuit attached below.

But the sensitivity very badly,measure,adjust the inductors and equal = 90uV ( at 12dB SINAD)

I had some experience to adjust IC FM/IF MC3361 ( RF input 21.4MHz , IF 455KHz and sensitivity about 3uV at 12dB SINAD )
therefor I know how to adjust quadrature detector terminal.

the datasheet SA615 show sensitivity achieved 0.22uV and how can I have this value with my RF input???

thanks so much.

// i use ceramic filter is murata cfukf455ka2x-r0
sa.PNG
 

BigBoss

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Edit :It doesn't need a differential input, I didn't see..
 
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vfone

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Assuming the crystal is right on 20.945 MHz, and the output resonator resonates on 455 KHz, I recommend to replace the 455 kHz filters with 100pF capacitors, just to see if you get the sensitivity.
Otherwise should be no reasons the circuit don't work.
 

xandeyes

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thank for your replies. I will to try replace filters...
 

xandeyes

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sorry for long time I don't reply because I havn't time.
my problem is in the power supply. I have a capacitor 47uF close PS but too far with IC. If I add a capacitor close vcc pin, the sensitivity is very well.
 

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