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1-3 of 3 messages
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broadband receiver interference // DF'ing HF RFI
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by VE7NZ on October 2, 2009
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Hello All -
I have broadband RFI on my HF receiver using SSB and wonder if anyonne has seen the same and knows what it might be from:
1. It sounds like "open squelch" and shows n
o peaks or unique modulation at any intervals.
2. On 20m it is S8, 15M S5, and 10M S3.
3. It is very uniform in signal strength across each band.
4. I get a 2 S-unit decrease when not pointed East or West with my 3 el tribander.
5. It is 24/7 and is not coming from my QTH (I turned off the master circuit breaker and ran the radio off a battery to confirm). It has been occuring since I installed my rig a year ago with no change at all. Since I use mostly CW it has not been a priority to solve, but it is something I want to resolve.
Second question - I have access to battery powered analyzer with which I can walk the neighbourhood. Any suggestions for a small directional antenna i can build/use to expedite tracking it down?
Thanks, 73, Adrian VE7NZ
Vancouver, BC.
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RE: broadband receiver interference // DF'ing HF RFI
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by WB4BYQ on October 5, 2009
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I have had broadband rfi from electric blankets, battery chargers for boats, cars, that use the switching, computer regulation system. you will have to drive around your area with a radio and antenna, to find the source. use the attenuator on the radio to lessen the signal to narrow in on the source. also, a shorter antenna helps once you have found the general area of the rfi. study the fox hunting procedures that amateurs use, this will help. if you can get close the ac meter box, or service box on the house lay a very small dipole on the meter and see if the rfi source goes up in strength. once you find the source of the rfi, then you have do find the device.
common-mode chokes will be needed. see this information
or read the arrl rfi handbook.
http://atnm.mcars.us/HomeBrew/WB4BYQ/CommonModeChokes/
http://www.olympixcorp.com/rfchoke/ferrite.htm
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RE: broadband receiver interference // DF'ing HF R
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by WB6BYU on October 12, 2009
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Can you hear the signal on 80m? I was up in Vancouver a
couple months ago for a DF practice, mostly on 2m but the
international competitions also use 80m and someone may
have a hand-held DF receiver available. (The 2m receivers
may be handy once you get close enough to hear it on that
band also.)
The general solution for small DF antennas is to use a
loop. I've got a homebrew one around here that tunes
from 5 to 15 MHz, just using 3 or 4 turns of stiff wire
stuck through holes in a piece of wood - they are rather
simple to build, though some of the plans you see online
aren't that good.
One problem with using a loop, however, is that it relies
on finding a null. Once you get close enough that the
signal doesn't appear to be coming from a point source
(which can be quite some distance if it is radiated
from power lines) then the null gets indistinct and
the antenna becomes basically useless, except to sniff
around equipment to see where the signal is strongest.
Also they will couple to wires and other metal objects
in the area: in the OTHER city of Vancouver we found
on 80m that when we parked alongside the road the loop
coupled to the power lines, and the bearings to the
transmitter always corresponded to the direction of the
overhead lines, regardless of the transmitter location.
Do you only hear the problem when your receiver is in
SSB mode and not in CW? Or is it just not so much of
a problem when you use a narrow CW filter?
I have had cases where an interfering signal would only
wipe out parts of a band - 21.075 to 21.175, for example -
but I would be surprised if it affected the SSB frequencies
on several bands but not the low end for CW.
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