Mark V


 NB Mod






Noise Blanker Mod for Mark V by VK5EME

See also NB Mod for Power line Noise by VK5EME

See also NB Mod Info by W8JI (scroll down the page)

Doug, as you probably remember I spend some time a while ago doing a simple modification to the Noise Blanker as an interim to finding time to look at things more closely.  I have spent many hours in the past few months & have modified the NB to make it as good as the TS940S which I regard as having one of the best Noise Blankers.  I have just finished a 2 page modification to dramatically improve the Noise Blanker on the FT1000MK5.  I hope that it can help others that may have bad power line insulators enjoy HF on the MK5.   

The NB performance on the MK5 was found to be good to average when compared with many current model transceivers, but poor compared to older Radios.  The benchmark for comparisons was the Kenwood TS940S which has a very effective NB. 

Many Transceivers along with circuit diagrams were examined to determine what circuitry was used, & the effectiveness of the NB.  It was discovered early on that many of the older Transceivers that use a Diode gating circuit, had a much better NB than some of the more modern Radios that use a FET gate.  The MK5 uses Diode Gating so this may be why the NB works reasonably well.  I however was not able to use the MK5 under very severe interference conditions from leaky 11kv power line insulators adjacent to my location.  The TS940 was quite easily able to get rid of the noise most of the time allowing me to still operate on HF.  Not even the TS940 NB or any other radio will get rid of high frequency noise from electronic equipment such as Inverter Air conditioners, or from Corona discharge from power lines etc. 

Problems with the MK5

  •  Poor NB performance on Strong Power line noise

  •  Poor performance on very low level Power line noise around S1 level, masking weak signals.

  •  Audio Distortion on strong signals with the NB on. 

  •  NB Adjustment Range steps are too large making finer NB level adjustments impossible.  

    How Should the NB Work ? ( My Own Thoughts & Modifications )


    1/         NB AGC: Signals stronger than about S5 need to start making the NB AGC work.  This will cause lower distortion on a strong SSB signal which probably won’t be heard on a weaker SSB signal with a lower S:N.  As the SSB signal decreases, the NB effect needs to increase so that weaker signals can be pulled from the noise.  The NB AGC circuit time constant C2006 4.7uF was experimented with, but was found to be close to what is required for a SSB signal.  Resistor R2027 15kohm sets the NB feedback.  A 47k pot was fitted in place of R2027 to experiment with the feedback.  The best option was to short it out R2027 with a wire link to give more NB feedback.  This gave an AGC action starting at around S5, compared to S9 with the 15k resistor.   


    2/         NB GATING:  Excessive NB gating causes the distortion normally heard on stronger SSB signals.  This can either be lack of NB AGC, or the bias voltage on the NB gating transistor.  As we have now got the NB AGC working well, we can now experiment with the NB gate bias.  Next I fitted a 5k pot in the position of R2280 the NB gate bias resistor.  The best setting of the pot was found to be 1k5, the original value of R2280 being a 2k2.    A 1k5 resistor was then fitted in the R2280 position.  


    3/         NB LEVEL:  The NB level needs to be adjustable so that it can be set accurately, depending on the level of power line noise.  The MK5 has a A1 to A15 level that changes the voltage to the NB AGC circuit.  The circuit uses a D-A converter that has quite large voltage steps making fine adjustments impossible.  The NB only starts to work with a level of A12 to A13 & I wanted it to start working at a lower A level & have finer adjustments up to A15.  The solution is the modify the D-A circuit to make the steps smaller which then gave a A7 to A15 adjustment.  The voltages measured on Pin 1 of  the D-A Q5011 before & after the modification are shown below.   The solution is to fit a 47k resistor from the +ve side of C2005 to the +9v power rail. 






















































    Please Note.  The above modifications all need to be done to get the NB improvement.  Doing only one or two of the mods, will not work as they interact with each other.  ie. the NB AGC will affect the NB level.  The NB level mod will affect either the gating or NB AGC mods. 


    All modifications are on the IF UNIT PC board


    Final Comments


    1/         Transceivers can vary when manufactured & quite often may not have the optimum performance in the NB compared with an identical model.  Things like component tolerance, or receiver gain before the NB can & will affect the NB performance.  Some experiments to improve the NB on Transceivers recently, have revealed that SOT ( Select On Test ) resistors have forgotten to be fitted to the Noise Blanker gate circuit in the factory.  I would also suggest that you check the alignment of the NB IF transformers. 


    2/         Transceiver manufacturers need to put more effort into the receiver noise blanker design & alignment.  I believe that it is one of the most important parts of a good Radio receiver in our now commonly noisy environments. 


    3/       There is no reason why all these above adjustment points, other than cost, could not be incorporated in New design transceivers as adjustable electronic pots accessed by menu settings. 


    4/         Receiver AGC on the MK5 needs to be slower on the slow position for more comfortable listening on the lower HF bands.  It needs to have a fast attack, slow decay.  Another set of electronic pots & adjustments in menus would be worth the extra costs.  The TenTec Orion has the goods in this area. 

    Mark VK5EME


     Noise Blanker Mod for Power Line Noise on the FT1000MP Mark V:

    I have been experimenting & comparing the circuitry on various radios over the past weeks. The FT1000MP MK5 does not seem too good with power line noise especially on weak signals. The Kenwood TS940 was found to have the best noise blanker compared to many other radios. I have come up with a very simple modification that may be useful to many that have very bad power line noise but don't mind blanking it & putting up with slight distortion on strong signals. This mod will however only make NB A work & NB B will have very bad distortion on all signals. The modification greatly improves the ability of receiving weak signals using NB A. The mod will reduce most S9 power line noise to S1.


    1/ Short out Diode D2009 with a wire link ( Located on the IF-Unit PC Board )
    The diode is a glass type & is accessible between the IF Noise blanker coils T2001 & T2002. Just solder a wire link across the diode.

    2/ Make sure that coils T2001 & T2002 are adjusted for maximum as per the service manual. ( My unit was not optimum )

    This is an initial modification & further experimenting needs to be done with the NB AGC feedback circuit to reduce the strong signal distortion with the noise blanker on.
    I hope that this help some that require better noise blanker performance.

    Regards Mark VK5EME


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This site was last updated 04/22/20