[Elecraft] [KX3] Noise blanker comments

[Robert Vargas-KP4Y]

 Hi Wayne,
Thanks for the nice info on the KX3 NB operation. How does the much lower opposite sideband rejection limits the effectiveness of the KX3 in a competitive environment? I have always imagined that everything is good as long as a strong signal doesn't get closer than 1 khz. Am I understanding this right? What would be the IMDDR3 of something like the K3 or K3S at 1 khz spacing? I have never had any issues with the KX3 during contest with IMD, but then I have small antennas; therefore, signals are not very strong.
Thanks,Robert-KP4Y/W4

    On Friday, December 11, 2015 10:49 AM, Wayne Burdick <n6kr at elecraft.com> wrote:
 

 David,

The KX3's noise blanker is implemented entirely within its DSP. Ahead of the DSP are the mixer and its duplexer, which have a finite bandwidth, and possibly the roofing filters, which have much narrower bandwidths. Because of this, there's no way for the DSP to gain access to wideband data for blanking purposes. 

While this does reduced effectiveness on some types of noise, the blanker still works well on most. I use it every day at my QTH on noise ranging from telephone-pole ESD to appliances and computer peripherals. And because the blanker is strictly operating within a narrow bandwidth, it cannot easily be "pumped" by signals well outside the IF passband.

The KX3's narrowband filtering also gives it a big advantage in blocking dynamic range compared to other SDRs that have nearly unlimited input bandwidth. For example, Sherwood measured the KX3's BDR at 138 dB, compared to something in the low to mid 120's for "pure" SDRs. The KX3 is also fifth on Sherwood's list for 2-kHz IMDDR3, again because of the narrow roofing filter.

Since the DSP controls blanking, it may be possible to implement additional noise blanking algorithms in the future. That is definitely on our list. If you send us a detailed description of the types of noise you encounter, we could try to duplicate them in the lab during this effort.

73,
Wayne
N6KR


On Dec 11, 2015, at 3:59 AM, David Anderson <gm4jjj at yahoo.co.uk> wrote:

> Still interested in any comments about how the KX3 noise blanker is implemented, and if it could be improved to make it as effective as the wide band RF blanker in HDSDR.
> 
> I now have the SDRPlay tracking the KX3 VFO so that in the event of static rain QRN I can switch to the SDRPlay for good copy when the KX3 is useless.
> 
> 73 from David GM4JJJ
> 
>> On 9 Dec 2015, at 20:30, <gm4jjj at yahoo.co.uk> <gm4jjj at yahoo.co.uk> wrote:
>> 
>> I use my KX3 on 144 MHz (with external transverter). 
>> 
>> Comments regarding the KX3 Noise blanker:
>> 
>> It is effective for some kinds of power line noise and ignition noise, I normally leave it on at a setting of 6.
>> 
>> It is not effective at all with heavy rain or snow static. 
>> 
>> By way of comparison I have an SDRPlay dongle connected to the same transverter and using the HDSDR software can enable the RF noise blanker in that software and it can reduce an S9+20 rain static noise that masks all signals to almost zero and allows me to decode a distant weak CW beacon that is just above the noise floor. On the KX3, just S9+ noise no matter what setting used on the NB.
>> 
>> I wonder if the DSP noise blanking could be improved in the KX3 to blank such heavy static? Does the KX3 noise blanker work in the demodulated audio or the RF domain?
>> 
>> Many thanks.
>> 
>> -- David GM4JJJ
>> 
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