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   Home   Help Search  
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Author Topic: Noise Blankers & Distortion  (Read 3564 times)
N5IOS
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Posts: 9




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« on: March 25, 2006, 06:55:15 AM »

  Like many of you reading this, I have strong local intermittent man made rfi, most likely from the power poles.  I have found that  the noise  blanker on my Kenwood TS-50 will take most of it out.  However, it also distorts all strong SSB signals.  The noise blanker on my old TS-130S will take out the noise without distorting strong SSB signals.  However, the 130S has a lot of other problems (hi) that make using it a pain right now.  Does anybody know of a modern transceiver that has
 a noise blanker that: (1) actually works, and
(2) does not distort strong SSB signals?   I have asked lots of hams who have local noise problems about this on the air, and so far nobody has found an answer.
Thanks.
73,
Bob  
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W3LK
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Posts: 5639




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« Reply #1 on: March 25, 2006, 04:16:57 PM »

You will be much better off to call your local power company and work with them to fix the actual problem.

To answer your question, virtually all noise blankers introduce some distortion to one degree or another.

73,

Lon - W3LK
Baltimore, Maryland
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N5IOS
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Posts: 9




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« Reply #2 on: March 25, 2006, 08:25:44 PM »

Thank you for your suggestion, Lon.  My local power coop is also in the propane business, the internet business, and has no interest in or knowledge of rfi.        

The noise blanker on my old TS130S, as I said, does not distort strong SSB signals, and takes out most (nearly all) of the interference.  The purpose of my post was to see if anybody knows of a more modern hf transceiver with an effective noise blanker that might do the same.  Perhaps no such transceiver exists.  
73,
Bob  
   
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WW5AA
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Posts: 2086




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« Reply #3 on: March 26, 2006, 09:03:28 AM »

Bob,

If your Co-op will not help you out, contact the NM Public Utilities Commission. I'll just bet they will have the Co-op folks out in a Hurry. Find out where the most line noise is originating, usually a transformer or bad pole ground. I use a HT set at 139.50. These days the supervisor at the power company stops by every so often to make sure i'm not having a problem. Seems he doesn't like calls from the Public Utilities Commission. Good luck!

73, de Lindy
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N5IOS
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Posts: 9




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« Reply #4 on: March 26, 2006, 12:40:27 PM »

Thank you, Lindy, for your suggestion.
However, I had hoped that somebody had experience with a modern transceiver, with a functional noise blanker that did not create noticeable distortion on strong SSB signals.  I really wanted to learn about noise blankers rather than pwr companies, etc. (hi)
73,
Bob    
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W3LK
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Posts: 5639




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« Reply #5 on: March 26, 2006, 02:34:13 PM »

<< Thank you for your suggestion, Lon. My local power coop is also in the propane business, the internet business, and has no interest in or knowledge of rfi. >>

That doesn't matter. They are REQUIRED by federal law not to interfer with radio reception, they are REQUIRED to find the problems and fix them or risk big fines, which the FCC will levy against them.

If they won't make the effort, file a complaint with your state's Public Utilities Commission AND file a complaint witn the FCC.

This may be the long way around, but it is the best way in the long run.

73,

Lon - W3LK
Baltimore, Maryland
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W3LK
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« Reply #6 on: March 26, 2006, 02:36:26 PM »

<< However, I had hoped that somebody had experience with a modern transceiver, with a functional noise blanker that did not create noticeable distortion on strong SSB signals.>>

As I said earlier, virtually all noise blankers introduce distortion on SSB signals. Fix the underlying problem and the need for the noise blanker will go away. Smiley

73,

Lon - W3LK
Baltimore, Maryland
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N5IOS
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« Reply #7 on: March 26, 2006, 02:45:02 PM »

Thanks again, Lon.
However, I am interested in information about noise blankers - not pwr companies.
73,
Bob
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N4VNV
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« Reply #8 on: March 27, 2006, 07:12:17 AM »

If you have a rig with a "user" adjustable noise blanker, you can adjust it to the level of distortion in each occurence. (i.e. IC746PRO etc.)
 I think I read the the top of the line Ten Tec has such a noise blanker as you and all of us wish we had.  But I'm on a fixed income and pretty much stuck with the lower priced rigs.
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W3LK
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Posts: 5639




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« Reply #9 on: March 27, 2006, 07:56:55 AM »

<< However, I am interested in information about noise blankers - not pwr companies. >>

Then I guess you really aren't interested in solving the problem - just finding a way to cover it up.

Sorry I wasted my time and yours.

Lon W3LK
Baltimore, Maryland
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N5IOS
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Posts: 9




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« Reply #10 on: March 27, 2006, 08:23:06 AM »

Thanks, K4SFC, for your relevant reply!   The next time I buy a new rig it will have an adjustable noise blanker for sure.  I will also see what I can learn about the new top of the line Ten Tec - just out of curiosity (hi).  
73,
Bob

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AA4PB
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Posts: 14722




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« Reply #11 on: March 30, 2006, 06:18:11 AM »

Its going to be really difficult to get a good answer on noise blankers because there are so many variables. What works in one location may be worthless in a different location. One person can tell you the blanker in his receiver works great and someone else who has the same receiver will say the blanker is worthless.

In general, the more effective the blanker is at removing the noise, the more distortion it causes on strong signals. The best is probably to have a blanker that gives you some adjustment although I have found that the adjustment often gives me two choices; distorted signals without the noise or clear signals with the noise.

You might also want to investigate some of the external blankers that use a separate noise receiver and antenna so they can pick up your power line noise without being bothered by the other signals on the band.

Most noise blankers are designed to remove very narrow noise pulses with sharp rise and fall times. Automotive ignition noise meets this requirement and the blankers are often quite effective. Power line noise can meet this requirement and the blanker works or it can be wider and the blanker will be ineffective. I have an intermittant power line noise that changes from day to day depending on the humidity. On some days the 756PRO blanker is quite effective and on other days it does absolutly nothing.

The bottom line is that you shouldn't count on any noise blanker being effective on power line noise unless you take the radio home and actually try it on "your" noise. Even then, as in my case, you may find that your noise suddenly changes and the blanker becomes ineffective. That's why you are getting the advise that the best solution is to eliminate the noise at the source. That's not easy, I know.
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Bob  AA4PB
Garrisonville, VA
N5IOS
Member

Posts: 9




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« Reply #12 on: March 30, 2006, 05:55:00 PM »

  Thanks, AA4PB.  All points well taken.  By the way, does your 756 Pro have DSP at the IF stage?  I am curious if that helps on your noise at all.  My only DSP is "after the fact" - on the audio output.  My noise here is either full on or full off - all or nothing.  When it is on, the NB in either Kenwood takes most of it out - one with distortion, one without.
If I were a few blocks away, I'm sure the noise would be a little different.  There are places in this county where the HF spectrum is pretty quiet - but not many (hi).
73,
Bob      


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AA4PB
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Posts: 14722




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« Reply #13 on: March 31, 2006, 01:35:24 PM »

Yes, the DSP is in the last IF, inside the AGC loop. That helps when using the narrow filters as it keeps signals outside the filter passband from "pumping" the AGC and affecting the overall gain of the receiver. As far as the actual noise reduction filtering I don't know that it is any better than having DSP in the audio stage. The big advantage is being able to set the IF filters at any bandwidth you desire.
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Bob  AA4PB
Garrisonville, VA
AD5X
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Posts: 1578




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« Reply #14 on: April 25, 2006, 05:39:44 PM »

The way that most noise blankers work is that they turn off the signal-path (blank it) in the presence of impulse noise.  If you think about it, this is the same way that a mixer works.  I.e., the LO signal biases the mixing diodes on and off.  The result is that you get mixing products (sum and differences of signals with the LO and each other).  So the problem is that if you have other strong signals in the band, the NB can effectively mix these with the desired signal and noise, causing  mixing products that fall in-band with your desired signal.  So, as has been said before, you trade off impulse noise suppression against added distortion.  I.e., TANSTAAFL - there ain't no such thing as a free lunch.  Everything is a trade-off!  

Phil - AD5X
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