[Lf] Synchronous Noise Blankers

[Vittorio De Tomasi]

Hi Richard,
I saw the blanker circuit some months ago, and it is on my "to-do" list. 

However I still think that it is better to chase the noise source and to
stop it, rather than resigning to the use of noise blankers. 
Trying to locate noise sources using LF/MF receivers is a loss of time:
at these frequencies mains cables are driving the RF energy along their
path, and you can be easily misleaded. 

However the spectrum of noise sources often extends to VHF and up (I
remember a halo lamp pouring out noise till to 1.1. GHz !!!). On these
frequencies the direction finding of the source is straighforward, the
only problem is that you have to be reasonably close to the noise source
to hear it, because the radiated energy does not travel through cables
at these frequencies (the range can vary roughly from less than one
meter for small wall transformer power supplies to 10-20 meters for halo
lamps). Try to use a VHF scanner (with AM/SSB reception, of course!) and
a small dipole connected to it: maybe you will be lucky. Then silencing
the source usually becomes a matter of "social engineering", unless the
noisegenerator belongs to you! 
To solve problems, I usually show to the owner how much energy is 
radiating, and I draw some figures about the added cost to his mains
fee: it usually works...

I have somewhere a bookmark to an english site about RFI problems,
solutions and horror stories: as soon as I find it, I'll post it here.


vy 73

Vittorio IK2CZL



Richard Goodman wrote:
> 
> Gentlemen,
>     Get out your soldering irons.  Finally a project that met every
> expectation I had and then some!   I had looked at the Synchronous Noise
> Blanker by John Reed,  KA5QEP on the Longwave Home Page.    It looked kind
> of interesting.... I also spoke to Andre.  He sent me a letter and drawing
> showing some modifications that he made to this device.  To make a long
> story short,  I built this thing.  I've been having severe problems with
> line noise.  Quartz Halogen "Torchette" lamps were a big problem... but the
> killer was something that would come on for several hours every evening.
> It was super strong.... about half to 3/4 meter deflection on my RX320.  It
> totally wasted the entire LF spectrum from 60 KHz up above 300 KHz.  Just a
> huge raspy buzz.  Usually starts up about 5 PM and sometime goes until
> after midnight.  I tried locating it with an AM broadcasr radio but it
> seems to come from every electricial outlet  and all wiring in the house.
> I shut off every circuit breaker but it was still there! I think it's
> coming from a transformer located about 100 feet from the house (but I'm
> not absolutely sure).
>     This noise blanker almost COMPLETELY gets rid of it ... it's amazing.
> I went from total overlaod to being able to copy the AMRAD beacon perfectly
> (with Spectran).  You can barely tell the interference is there.... after
> awhile I switch the filter off to see if the interference has gone away
> (but with the filter out it's as bad as ever).   It seems to raise the
> noise floor just a little bit but I'm still able to do serious weak signal
> work with the filter running.... BEST WORKING PROJECT THAT I'VE EVER BUILT!
> 
>         Thanks John Reed,  KA5QEP and also to Andre, N4ICK  !!
> 
>                 I EAT TORCHETTE LAMPS FOR BREAKFAST NOW  !!!!!!!
> 
>                         73
> 

-- 
*************************************************************************
Vittorio De Tomasi         ik2czl at amsat.org
Home page:                 http://space.tin.it/scienza/vdetomas 
My DSP page:               http://www.freeyellow.com/members/padan

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