Re: Noise blanker test.

[Mike WA8BXN]

Jack,
 
With a hope to be helpful by providing peer review on the experiment that
you are trying to do, I offer two quick observations. One is no mention of
the input amplitude of the noise pulses, and particularly varying their
amplitude. Second thought is that having a real signal to which you are
adding the noise pulses to might give more information than just the effect
your noise pulses have on no signal receiver noise. A noise blanker could be
entirely removing the noise pulses but that leaves holes in the resulting
signal you are hearing (the no signal noise of the receiver). You would hear
something (changes in the background noise) but not the noise pulses
themselves.
 
I hope some of these words may ring a bell or light a bulb giving more
insight on your results or other experiments you may want to do.
 
73 - Mike WA8BXN
 
 
 
 
 
-------Original Message-------
 
From: wa9fvp
Date: 09/30/11 13:42:27
To: [hidden email]
Subject: [Elecraft] Noise blanker test.
 
I made an attempt to plot the noise blanker performance and log the results
In an Excel spread sheet. I found that the test was in valid so I used a
Different approach.
 
The test involves using a function generator that's built into my Agilent
DSOX3024. The generator is set for pulse mode with a 200mv P-P pulse
Repeating 15.5 every 15ms. The pulse rate is similar to a car with a bad
Ignition system speeding by your ham shack. To insure that there's no RF
Getting back into my very expensive oscilloscope, I connected the generator
Output to the K3's RX port. The settings were adjusted by listing to the
Noise at the speaker.
 
I determined that without the DSP or the I.F. Noise blanker turned on there
Are "sweet" spots and "hot" spots. That is the sweet spots are where the
Pulse width is adjusted so that the noise is minimum and the hot spots are
Where the noise is maximum. I found that every 70ns, there’s a sweet spot
And 35ns form the sweet spot there's a hot spot. Adjusted the pulse width
>From 20ns to 1 ms and the hot spots and sweet spots were right on target.
 
So what does this mean? There conditions where you can have a motor, car or
Any electrical device that generates a pulse with in the sweet spot will
Never be heard on you K3. On the other hand there are conditions where the
Noise source generates a pulse width that’s with in the hot spot, will the
Noise blanker effectively reduce the noise.
 
In my original test I didn’t know that there were sweet and hot spots. I
Ran the test by simply turning the NB and adjust the NB level. My new
Approach is a lot more simple and doesn’t require checking every sweet and
Hot spot
 
All settings from NAR1 to NAR4 are totally useless. It offered no noise
Reduction regardless of the pulse width and pulse rate. Settings from NAR5
To NAR7 were somewhat effective but the noise reduction was spotty and the
Noise level would vary every 5 or 6 seconds.
 
MED 1 and 2 are useless settings and MED3 is spotty. MED4 to MED7 reduces
The noise considerably. The same is true for WID 1 and 2. Usless! WID3 is
Spotty and WID4 to WID7 are the best settings.
 
 
http://elecraft.365791.n2.nabble.com/file/n6848682/k3_blkr.bmp 
 
-----
Jack WA9FVP
Willco Electronics
--
View this message in context: http://elecraft.365791.n2.nabble
com/Noise-blanker-test-tp6848682p6848682.html
Sent from the Elecraft mailing list archive at Nabble.com.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft 
Help: http://mailman.qth.net/mmfaq.htm 
Post: mailto:[hidden email]
 
This list hosted by: http://www.qsl.net 
Please help support this email list: http://www.qsl.net/donate.html
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[alorona]

Hi, Jack,

> The test involves using a function generator that's built into my
> Agilent DSOX3024. 

Ah, excellent choice. :^)

> The generator is set for pulse mode with a 200mv P-P pulse
> repeating 15.5 every 15ms. 

I don't know what this means.


> I determined that without the DSP or the I.F. noise blanker
> turned on there are "sweet" spots and "hot" spots.  That is the
> sweet spots are where the pulse width is adjusted so that the
> noise is minimum and the hot spots are where the noise is
> maximum. 

I think what you're probably hearing is the sin(x)/x spectrum of the pulse.
Every pulse has a spectrum that looks like "sine x over x", or "sinc". Page 9 of
this document: http://cp.literature.agilent.com/litweb/pdf/5989-4839EN.pdf 
shows the spectrum of a repeating pulse. You'll notice that it has peaks
and nulls, exactly as you noted. Instead of adjusting the pulse width to observe
the peaks and nulls sweeping through your receiver, you could have left the
pulse width alone and tuned the receiver across these peaks and nulls. 

Believe it or not, it's more difficult for the receiver to eliminate pulses when
you're near a null than when you're at or near a peak. This has to do with the
noise blanker threshhold.

R,

Al  W6LX
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html