Yaesu FT 950 CW 1,4kHz roofing filter

After 2,7kHz roofing filter has been build in

 and succesfully tested in various contest,s  like WPX, Russian DX  Contest  and  CQWW160m  I have  decided to build narrower roofing filter which will be more suitable for CW.

                                        

I have chosen compromise between bandwith and filter 50 Ohm  impedance and therefore I have constructed 1,4 kHz wide roofing filter. BW -6dB  1497Hz  - 60dB  9284Hz. See pictures 2,3 and 4. The spectrum has been taken from   TP 1066   (see Service manual).  After the measurements I was suprised because measurments results are impresive on spacing 2 kHz. If I compare these results with Sherwood test,s  they are comparable with K3, TS 590SG  and   IC7610  Sherwood results. I allow  one or two  dB  tolerance in my measurements  because I am using ham equipment and no professional HP instruments as Sherwood did. A great help in construction this roofing filter has been  found in Horst Steder DJ6EV  article  » Monolitihic Crystal Filters » and his  » Crystal Ladder Filter Programm » Dishal« - See picture 1.  With  smaller changes this CW roofing filter can be used also in FT2K transceiver.

Measuring with :  1.st preamp OFF ; 500Hz Bandwith; Roofing 1,4KHz; AGC Off , Test band is 7MHz ;

MDS -127 dBm Noise floor

RMDR  (2kHz) 93 dB  (5kHz) 102dB

IMD3  (2kHz)  94dB    (5kHz)  95dB

Blocking  spacing 100 kHz : greater than 137 dB

 Lo noise spacing 10kHz : 139,9 dBc/Hz.

According to the experts’ opinion (e.g. Rob NC0B and Tom W8JI), the IMD DR3 of 85 dB is enough for CW. Thus my 2 kHz IMD DR3 94 dB results are excellent.

Picture 1:    Simulation CW filter with Dishal DJ6EV  programm

Picture 2 :  SSB and CW roofing filter connections

Picture 3 :  More than 60 dB filter ultimate attenuation

This  Filter Characteristic Diagram is comparable to the IC-7851 ---1.2kHz Optimum Roofing Filter.

Picture 4:    -6db  CW roofing filter bandwith

Picture 5: Measurments on 450kHz IF - TP 1054

I also  decided  to modify the AF passband. You can simply get rid of some hiss which sounds like a white noise  to roll off the highs with    820  pf  cap added parallel to capacitor C1571 . The receiver is now super quiet ( See picture 6 )

Picture 6 : AF modifications

The same Roofing  Filter can be  with minor changes used for up conversion receivers  with first  intermediate frequency (IF)  between 60 in 75 Mhz  like : 

        ICOM IC : 756, 765, 775, 7400, 7410, 7700,7850,7851

Kenwood  TS: 450, 850, 870, 950

                  Yaesu  FT :  450, 847, 897, 920, 1000D, 1000MP, 9000

Warning !!! Changing any hardware inside FT950 or FT2K will void your warranty. I am not responsible for any hardware failure. You made this mods on your own risk.! This modification requires a high level of soldering skill, possibly beyond that normally possessed by the average HAM. Professional assistance is advised if you are not confident that you have  this ability.