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) arenbt 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@contesting.com
Cc: cqkg8co@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
------------------------------
Message: 2
Date: Mon, 29 Jul 2013 13:07:04 -0400
From: Brian Sarkisian <cqkg8co@gmail.com>
To: towertalk@contesting.com
Subject: [TowerTalk] Wireless Internet RFI
Message-ID:
<CAKhJrARryLaHFfhO+LBEhS-017NypUAvCtjxn3REaRqsVqyi6A@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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