[RFI] RFI/EMI MAJOR Problems
jim at audiosystemsgroup.com
Thu Nov 30 01:59:13 EST 2006
>1) Get the antenna off of the roof and out into the backyard away from the
>house. You are essentially radiating back down into your house and every
>wire in your attic is acting like an antenna. The further away from the
>house you mount your antenna, the better off you will be.
I disagree. N3OX was right on target -- the wire that you are calling "ground" is
part of the antenna, and it's carrying the full the antenna current and is
radiating into your home equipment. Resonant, elevated radials are a good move.
That one move all by itself may do most of what you need. Study the ARRL Antenna
Book and ON4UN's book for detailed advice on those radials.
>2) Your choice of toroid material is not optimally suited for attenuation of
>HF signals. According to Amidon's data sheets, #43 material has optimum
>frequency attenuation between 40 mhz and 400 mhz. In general, that is above
>the frequency range you are attacking. I have had good success with #77
>material, which has maximum attenuation from 0.5mhz thru 50 mhz.
WRONG! See the measured data for multiturn chokes and tutorial on my website.
This data was done by a very good engineer with excellent HP gear. Amidon is a
sales and marketing company. #31 is by far the superior material for HF
suppression -- it is good from the AM broadcast band to above 10 meters, and is
greatly superior to #77 or #78. #43 is just as effective as #31 above about 7 MHz.
>3) Are you using clamp on toroids or donuts in all of your applications?????
>Using donuts allows you to get 10-12 wraps of cable around the ferrite
>material and places a significant amount of cable "surface area" in contact
>with the ferrite when compared to the use of "clamp on" ferrites. In other
>words, winding a cable on a 2.5" OD (outer diameter) donut uses about 8-10
>inches of cable at a minimum. In order to achieve the same amount of
>supression in a cable using clamp on ferrites, you would need to clamp on
>the equivalent of 8-10 inches of ferrites .
You are correct about turns, but it has nothing to do with "contact" -- the
ferrite material simply provides a path for magnetic flux that adds a very lossy
parallel resonant circuit in series with the wire that runs through it.
>4) Get everything clean without using the linear amplifier.
And start all over when you turn on the amp? That doesn't make sense to me. If it
isn't broken, the primary contribution of the linear from an RFI point of view is
to increase the voltage or current by 10 dB or so in the victim circuit. Since
virtually all detection is square law, the difference translates into 20 dB more
detected signal. Also, the original post noted that things got really bad when he
got past 500 watts, which is less than 5 dB down from 1500 watts. This means that
he will fix all of the problems caused by that power increase simply by reducing
the field strength in the house by 6 dB. The radials stand a pretty good chance of
doing that and more.
Jim Brown K9YC
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