YAESU FT 950 SSB 2,4Khz roofing filter

As a backup to my FT 2000 radio I am using a FT 950, which has the same 69,450MHz first IF frequency. The  first IF stage features three roofing filters (15 kHz, 6 kHz, and 3 kHz) automatically selected by mode. Each roofing filter is a four-pole, fundamental-mode monolithic crystal filter design. Unfortunately, some choices made in the first IF design of the rig left is with quite a poor performance score in one area - close-in high-strength signal handling capability. The original Yaesu 3 kHz filter measures only about 7 kHz wide at -6dB.  After Jeff AC0C wrote that  FT2K/FT950 excellent NS roofing filter in no longer in a production I have decided to make my own roofing filter. Roofing filter attenuates and reduce IMD3 products and DSP has less bandwith to process.

After I successfully installed in the second IF 450kHZ a selection of  2 (two)  Murata +/- 2kHz CFWLA450KJFA ceramic filters placed in a cascade and  therefore reduced IF noise and IF image(see picture 1) ,  I also decided  to improve the FT 950  input IMD performance with my own SSB roofing filter.  The same roofing filter can also be used for FT 2000 receiver.

Picture :1  New 450Khz  IF

A homemade SSB the 4 pole 50 Ohm Cohn crystal filters of 2,7 KHz bandwidth at  6dB has been modeled with a AADE Filter design V4,5 program and is built from discrete 3rd overtone crystals. Crystal parameters:  3rd overtone  FL 69,450 Mhz , RR = 20 oHm, C0 = 4pF, FL= 5ppm, package UM1  (see picture 2 and 3)

Picture:2 Cohn  4 pole filter  modeled with an AADE Filter design

Picture:3  Input impedance modeled with an AADE Filter design

To improve the impedance mismatch between 1st mixer and roofing filter I added a diplexer to properly terminate the roofing filter. Diplexer terminates the impedance of the roofing filter to the first  mixer in a wide frequency range. To compensate filter loss I have added ultra-low noise (0,55dB) and  high performance MMIC LNA- SPF 5189Z (or MMIC PGA 103+)with output third order intercept point typ +38.5 dBm. To lower the MMIC  gain a 4dB T attenuator has been built at the output.(see picture 4)

Picture: 4  The 69,450Mhz roofing filter circuit

Unlike Jeff AC0C, I decided to improve the ultimate attenuation and   installed my new 2,7 kHz roofing filter before the original YAESU 3kHz XF1004 filter.( see picture 5)

Picture: 5 

Before the 2,7 kHz roofing filter has been built in the Yaesu 3 kHz filter measures about 6-7 kHz wide at -6dB. The spectrum is taken from the 2nd IF TP 1056 and shows  the filter shape of the original FT filter.( see picture 6)

Picture 6 : Spectrum taken before 2,7kHz  roofing filter has been built

Preparing the 2,7 kHz roofing filter for installation

1.       Locate the working area on the PC board ( see picture 7)

Picture 7: Working area

2.       Unsolder SMD capacitor C 1583 (see picture 8)

Picture: 8

3.  Cut the PCB trace between T1026 and original Yaesu XF 1004 3kHz filter (see picture 8)

4. Solder the input coax center conductor to the center pads of T1026 (see picture 8)

5. Solder the input coax shield to the transformer T1026 casing.(see picture 8,9)

Picture: 9

6. Solder the output coax center conductor to the input pad of original XF1004   Yaesu 3 kHz filter (see pictures 7,8,9)

7. Solder the output coax shield to the ground near filter XF1004 (see pictures 7,8,9)

8. Solder back SMD the capacitor C 1583

9. Connect 9V DC to the new filter from pin 14 - J 1005 ( see pictures 10,11,12)

Picture:10

Picture: 11 

Picture:12

9. Trim T1026 and T1033 to maximum signal level

After the 2,7 kHz roofing filter has been built in ,(see picture 13)  the front end is far more selective and a new filter measures about 2,7 kHz wide at -6dB and 8kHz at -50dB. The spectrum is taken again from the 2nd IF TP 1056 and it shows a new filter shape .(see picture 14)

Picture: 13 Roofing filter  build in

Picture :14  Spectrum taken after 2,7kHz roofing filter has been built in

More about the built in procedure can be seen from the pictures above.

After this modification and  adding a selection of  2 (two)  4kHz Ceramic filter in second IF 450kHz ,   I measured IMD and RMDR dynamic range at offsets of 2kHz  and 5kHz  with   2 x -6dBm  DC4KU   HF- Zweitongenerator FA-2-HF.  Two-tone third order dynamic range (IMD DR) is the diference between MDS and the levels of two interfering signals causing IMD products 3dB over the noise floor. RMDR is Reciprocial mixing dinamic range , measured as a 3dB increase in noise floor.    See Picture 15 

Picture 15: DC4KU  Two- tone RF generator -6dBm

Results of two tone IMD testing - 1.st preamp OFF ; 500Hz Bandwith; Roofing 2,7KHz; AGC Off , Test band is 7MHz ;

MDS = - 128 dBm, 
Blocking above noise floor @ 10 kHz ,measured as 3dB increase in noise floor  107 dB
IMD2 Dinamic range second order on 14 Mhz    = 76 dB

Spacing offset:                                              IMD DR3:                    RMDR              

2  kHz                                                               86dB                       90 dB           
5 kHz                                                                88dB                       98 dB              

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 86*dB results are very good.

I have been testing the new roofing in CQWW_2019 CW/LP   contest with more than 2010 QSOs  and I was really satisfied with a new installation. I used the radio on the air  several days before  CQ  WW Contest and great difference was noted  between the 6kHz filter and the new 2,7 kHz filter at dynamic range

With a little changes the same filter can be build also in FT2K

Warning !!! Changing any hardware inside FT950 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.

Note for simplified installation  10.08.2020

I found that is much easier  to  unsolder (zero) oHm  SMD resistor R 1393 to insert  roofing  filter in cascade with original Yaesu 3kHz roofing filter. See pictures  below.

FT 950 narrow IF filter

I am using the FT 950 as a second rig as a backup for my FT 2000. The FT 950 use  the same 450 kHz Ceramic filter as the FT 2000 transceiver . The CF 1001  has been built in the second 450kHz  IF with a BW of about 15kHZ, because the FT 950 can be used in FM as well as in AM mode. 
see: Picture 1

Picture 1: FT 950 IF schematics.

However for SSB and CW the original filter CF1001 -CFWLB450KE1Y is too wide to reduce the signals that are reaching the DSP.( see Picture 2)

 Picture 2: Original IF (Measured on TP 1054, Roofing 15Khz).

Because I don't work on FM and AM mode I decided to install a selection of 2 (two) Murata +/- 2Khz CFWLA450KJFA ceramic filters placed in a cascade.

Picture 3: Murata +/- 2Khz filters placed in a cascade.

Cascaded Murata CFWLA450KJFA filter will reduce much better stopband suppression and bandwidth on SSB and CW is reduced to 4Khz. Therefore it will also reduce IF noise and IF image. FM will be degraded, but AM not excessively.  Normal 2,4 kHz SSB and CW will not be affected. After these changes the signals will be better managed with a DSP.

Picture 4: New bandwith (Measured on TP 1054, Roofing 15Khz).




Preparing the new Cascaded Murata CFWLA450KJFA 4kHz filter for installation:


1. Locate the work area on the PC board (see picture 5)

Picture 5 :  Work area location.

     2. Unsolder SMD resistance R 1415, 0 Ohm (see picture 6)
3. Unsolder SMD resistance R 1433, 390 Ohm (see picture 6)

Picture 6 : 

4.   Stick with glue 2x new  4kHz Murata filters on the existing original  filter CF1001 (see     picture 7).

5.   Connect with a thin  wire the output from a transformer T1027 with the first  new 4Khz     Murata  filter input.

6.   Connect with a thin wire the output from first new 4Khz Murata filter with an input of the     second 4Khz Murata filter.

7.   Solder back with a thin wire the 390 Ohm SMD resistor between the second  Murata  4kHz   filter output and T 1030 input.

8.   Adjust carefully transformers T1027 and T 1030 for maximum S meter deflection 
 (see picture 8).

Picture 7: The final filter installation.

Picture 8 : 450kHz  filter layout and  T1027 and T1030 transformer location.

One Murata CFWLA450KJFA filter has 6dB attenuation, but I did not detect a large difference in signal strenght after the new filter, which has been built in. 
Because the FT 950 receiver is too sensitive on low bands, I decided, after this modification not to increase an IF gain.  However, we can change the IF gain in the FT 950 Hidden Menu setting E01iGN to E10iGn if we want.  (Please see FT 950 Technical Supplement, page Alignment –IF Gain adjustment.)

Please carefully note that this  Hidden service menu is accessible for maintenance for an technician experts. More about the build in procedure can be seen from the pictures.

After building new filters it is still possible to receive AM, but FM will be degraded. I have been testing my receiver in CQWW_2019CW contest with more than 2000 QSOs and I was really satisfied with the new installation.

CFWLA450KJFA filter can be purchased online in Poland at: https://www.hesta.pl/pl/

Picture 9 : Murata  4Khz filter specifications.

Warning !!! Changing any hardware inside FT950 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 an average HAM. Professional assistance is advised if you are not sure if you have this ability.