[TowerTalk] Wireless Internet RFI

[Patrick Greenlee]

Wire a temporary lashup to let you easily and quickly temporarily run your 
receiver on battery power and then back to power supply (assuming 12 volt 
supply)

If the noise is from the power supply it will be obvious by its absence when 
you switch over to battery and turn the PS off. While running the receiver 
on battery power throw the main breaker in your breaker panel to the OFF 
position.  If any of the RFI goes away it is something in your house and 
going through the breakers one at a time with the main breaker on (killing 
one breaker at a time) you may be able to isolate which circuit is powering 
the offending RFI device.

On receive only most rigs use just a few amps at most so running the rig for 
the time required to do some trouble shooting doesn't require a monster 
battery.  A battery out of a lawn mower or similar should do the trick. If 
you have one of the handy dandy "jump start" thingies that will do nicely 
(this is the battery in a plastic carry enclosure NOT the start position of 
a HD battery charger.)

If the offending signal(s) arenb t killed by turning off your main breaker 
and temporarily disconnecting your phone line before it goes in the house 
then you need to do some DF work to determine the source.  A small loop 
antenna on a small battery operated gen coverage RCVR will help locate the 
source.  If you determine by aligning the null off the loop a line of 
position then move at right angles to that line until you get a hefty change 
of bearing in the null.  This establishes a second line of position. Where 
the two lines cross is where the source is. As you approach the source you 
need to redo the two lines of position to get a more accurate determination.

Patrick AF5CK

-----Original Message----- 
From: Earl Morse
Sent: Tuesday, July 30, 2013 7:36 AM
To: towertalk at contesting.com
Cc: cqkg8co at gmail.com
Subject: Re: [TowerTalk] Wireless Internet RFI

Brian,

Selecting the right bead is only the small part of the problem.  The more 
important part is knowing where to put the bead.

You didn't describe the noise other than that it is occuring at lower 
frequencies.  From this, my first assumption is that you are dealing with 
switch mode power supply harmonics.  They will sound kind of broadband and 
occur ever 50-200 kHz or so.  Anyway thats a good place to start.

As for the ferrite, the most common ferrite out there is some flavor of 
Fair-Rite Type 43 with a permeability of 800-850.  It is used by electronics 
manufacturers for wideband noise suppression especially in the 20-200 MHz 
range.  It is the core you will find molded into or snapped onto common 
electronics cables.  It is also the most common core rolling around in the 
junk boxes at hamfests.  Though it is optimized for a higher frequency range 
it will work at lower frequencies.  Find the biggest one you can and then 
put as many turns of cable on it as you can fit.  When you find some 
improvement then you can either add more turns, another core, or change to a 
different material to optimize the results.

Good luck.  Remember that consumer electronics are completely cost reduced 
and many manufacturers will happily delete RFI suppression components 
because it doesn't affect performance and most users won't notice the 
increase in RF emissions.

Earl
N8SS
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Message: 2
Date: Mon, 29 Jul 2013 13:07:04 -0400
From: Brian Sarkisian <cqkg8co at gmail.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Wireless Internet RFI
Message-ID:
<CAKhJrARryLaHFfhO+LBEhS-017NypUAvCtjxn3REaRqsVqyi6A at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

I recently had an internet wireless antenna/unit installed as our DSL was
painfully slow.

Now I notice RFI in the AM broadcast band and into the 160 meter band.
There may more
RFI issues on other bands however at this point I haven't noticed anything.

I see that Fair-Rate makes a series of "New Low Frequency Suppression Cable
Component
ferrites, though I am not sure what I should purchase.

It looks like that I should be looking for a "certain impedance" for a
particular frequency.

Any help would be appreciated.

73 de Brian, KG8CO


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