Thursday, February 26, 2009


I was listening to 160 this morning. I was listening to OA4TT run some JA's and any other takers. My band noise this morning was running about -120dBm and the OA4 was about ten dB above the noise perfectly Q5

All of a sudden I was greeted by this:

I occasionally get this noise, and it basically takes out anything in the pass band. It usually only lasts for a couple minutes, but during that couple minutes I'm screwed. I clicked on the NB and here is what I saw

Virtually all the noise was eliminated and my noise floor returned to -120dBm and the OA4 was perfectly readable again. So the radio has a noise blanker, what's the big deal?

The big deal is the noise blanking is done in software. The noise is eliminated, period. It does not leave clipped holes in the signal like an analogue noise blanker and it does not affect the AGC. There is no noise bleed through into the pass band at all, and virtually no distortion. The noise floor is not affected. It is absolutely amazing. The OA4 was running a +1 split on his pileup. During the course of my listening there were a couple of the wide band CW Yaesu rigs that started banging away at him with signals in the -60 dBm area (ten over 9). With the NB on there was absolutely NO AGC pumping or added distortion even with these loud wide signals tempting fate. Here is a real change in how ham radio is done, a noise blanker that truly just eliminates noise without adding additional spurious response. This is the difference between making a contact and no contact. I have never experienced a blanker that works so well. Because it has no "parts" in hardware and is totally mathematical its behavior is perfectly characterized. You may love your knob, but I love the absence of noise. Noise messes with my demeanor. It makes the radio experience go from fantastic to funky in a NY minute. To tell the truth with the advent of point and shoot tuning I ain't much on knobs either.

This brings up another promise as yet to be fulfilled, what about eliminating static? What if you place a "watch receiver" somewhere in the pass band that listens to just static, that gives you the information of what the static looks like. Suppose you invert that signal and add it to the signal you are listening to, such that the static in the signal is the exact opposite amplitude of the inverted static? You would cancel the static. Since SDR is not real time but a little bit behind real time (due to processing) you have the luxury to do this kind of manipulation in software that you could never do in hardware. This is not yet implemented, but all the pieces are present. Given how well the noise blanker works can a static blanker be far behind? Here I think is one place where the Flex approach to DSP shines. Let's say your legacy radio has DSP. The question is does it have enough DSP? Is there enough room in the DSP to keep adding and adding features? Is the DSP fast enough to accomplish something like a static blanker? Clearly if the DSP is your computer you have plenty of room and speed, and if you run out of room and speed its a simple matter to increase both parameters.

Signal are always present. If a VK is sending on 3505 at 12 in the afternoon his signal is present to my radio. The question is can I get far enough down in the noise to hear him. One day I did work a VK on 80M at 12:49 in the afternoon. In the summer we are limited in our DXing by static. Suppose you could eliminate the static. Take a look at the above pictures and imagine the possibility


I captured said NOISE on audio and converted to an MP3 file I turn the blanker off and on several times


(note: the above is really only 2 pictures one with the noise and one after the noise was blanked. because of the way I do screen capture I have to dump clip board memory between screen captures which is kind of a curly shuffle. The before and after pics were the same so I just made 2 screen dumps for illustration, but the story is accurate)