Yaesu Ft 897D audio hiss reduction

I   have  owned  Yaesu FT 897D rig  that  they  seem to have to much audio hiss or more correct description :  »Noise in  the back ground audio«. This hiss-type noise is a little irritating if you use sensitive HI-FI headphones. After I have added recommended feedback circuit to power audio amplifier TDA 2003 ; see my Blog: ( FT 920, FT 897D and FT1000MP audio white noise reduction) I have found, that some hiss is still present. So I decided that the most effective way of addressing the rig noise was to modify the AF passband. You can simply get rid of it to roll off the highs with some paralleled caps added on the audio chain.(See picture 1)

Picture 1: FT 897D audio preamplifier Q1120

Preparing the FT 897D for adding some elements.

1. Carefully remove the top cover and gently remove the speaker cable.
2. Locate the work area on PC board ( see picture 2)

Picture 2:  Preamplifier Q1120 location

1. Solder 390 pF SMD capacitor  parallel to C 1456( 100pF)

1. Solder 560pF SMD capacitor parallel to C 1609 (100pF)

1. Connect the speaker back and close the top cover.

Before adding some elements simulations were done in EWB program which is a fast utility for these kind small changes on this circuit.  I decided on a 2,3 kHz corner frequency target because I often do SSB. The best way is to parallel the needed value with the stock caps.  In this way, no components need to be removed.  The cap sizes are in the SMD 0603 category. 

My observation after this mod is that the hiss level is far less with the cap changes. I also made some measurements (see picture 3)

Picture 3 : New  6dB  audio spectrum taken at headphone AF Output  - Mode FM

Warning  !!! Changing any hardware inside FT 897D 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.

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 920 diplexer

To  improve  impedance mismatch between the first mixer and roofing filter  a diplexer has been added to properly terminate the roofing filter. The diplexer terminates the output impedance of the mixer to the input impedance of the roofing filter in a wide frequency range. 

Picture 1

I decided to insert a SMD diplexer at the input of Inrad roofing filter.  The added SMD diplexer was built  near  roofing filter. 

Picture 2

Warning !!!  You made this mods on your own risk. I am not responsible for any hardware failure.This modification requires a some 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.

How To simply improve FT 950 Receiver Dynamic Range.

After I measured the receiver noise level on my antennas and I measured level between -73dBm and -121dBm (S-9 to S-1) on 500Hz  CW  bandwith, I found out that the receiver is too sensitive on 160, 80 and also on 40m. 

Picture 1:  Noise level measured on my antennas.

Picture 2:  ITU Noise level guidance

The noise from antenna was measured  with a calibrated S meter.
The antennas used in the Noise level determination were as follows:

• 1,8 MHz   40m long Inverted L
• 3,5MHz    20m long Inverted L
•    7MHz    Dipole
• 14 MHz    3el.Beam
• 21 MHz    3el.Beam
• 28 MHz    3el.Beam

Measurements were made at several times and with attempts to measure on the same frequences at similar day times.

How Much sensivity  Do We Need ? Arbitrary assumption are made: Add to measured receiver noise level 15dB. Oversensivity makes no sense ,only HF receiver Dynamic Range gets worse.

On the bands from 160 to 40m you should not use a preamp att all, because the antenna noise at these frequencies is still above the noise floor.  In order to improve the dynamic range I always switch on at lower bands IPO and  6-18 dB  antenna attenuator, which significantly improves the received signal-to-noise ratio. Also note that IMD3 products drop x3 by the selected attenuator value. For example: 6dB attenuator increase  IMD 3  for 18 dB !!.

In the FT 950 receiver  I have also  reduced   IF gain for about 10 dB. ( see  FT 950 Tehnical Supplement IF Gain Adjustment- Page ALIGNMENT 7 )

Alignment Parameter E-01iGn , E-02iGn and  E-03iGn   represents the receiver's  IF gain for 160, 80 and 40m. Turning  CLAR (VFO B)  Knob clockwise  increase the value and   a higher number  will reduce the IF gain. On 160 ,80m and 40m  I increase the value by 10. One value equals approximately 1 dB. Please be carefully, because this Hidden service menu is accessible for maintenance for an tehnican experts. 

You made this mods on your own risk. Do any of the setting at your own risk  ! 

Keep away from any modifications  if you are not sure.  

This modification requires a high level of  skill, 

 possibly beyond that normally possessed by the average HAM. 

Professional assistance is advised if you are not confident that you have  this ability. 

I could not be responsible if you,re doing something wrong. 

FT 920, FT 897D and FT1000MP audio white noise reduction

 

The  FT 920, FT 897D and FT 1000MP has the same audio amplifier TDA2003, where  white noise was rather disturbing. Therefore I added a recommended feedback  according TDA 2003 data sheet description. According to the recommended  formula, the RC circuitry cuts tones higher than 3 kHz. The additional serial RC circuit can be directly soldered between pins 2 and 4 of theTDA2003. See picture 1

For  SSB ( 2,7kHz)     Rx= 39Ohm    Cx= 270nF