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.