High performance SSB filter for Direct Conversion RX
18.03.2006 OH7SV

Prototype of the high performance SSB filter

SSB filter response

This filter is using 3rd order active high-pass and 7th order passive low-pass with three elliptic zeros.
The design goal was to get better filter compared to original active filter used in my direct conversion TRX.
Th very first prototypes were contructed with single ended passive coils, but they picked up too much interference.
The filter shown here is using coils differentially to avoid the magnetic interference and the results are very good.
- approx. 20 dB lower noise =>  20 dB better dynamic range
- much better shape factor (2.6 => 1.77)

Short form performance
Band width 2.4 kHz @-6dB see response
Good shape factor 1.77 (-60dB / -6dB)
Insertion loss 0 dB
Ultra low noise, total output noise only 0.8 uVrms (300 Hz...3 KHz) see output noise density [nVsqr(Hz)]
Very high dynamic range 130 dB
Very good stop band rejection > 90 dB

TOKO 10RB inductors are used in the prototype
See schematics

Listen a sample SSB recording during a contest in 80 m band
Listen a sample SSB recording during a contest in 40 m band