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For some reason this didn't get reflected. Lets try again....
> Gerry,
>
> A couple things. First, I've never heard of an FCC requirement regarding
> antenna separation from neighbors, living spaces, etc., as long as you meet
> the applicable RF exposure requirements. You can check the amateur
> regulations on the web (I don't remember the address, but there's a link
> somewhere on the www.fcc.gov website). There's also some good info you can
> download from the ARRL website (www.arrl.org).
>
> Computer speakers are generally pretty straightforward. Start by adding
> clamp-on ferrite cores at the speakers themselves on both the audio and
> power leads. Remember that you need several turns of wire through a typical
> core in order to have sufficient inductance to have much effect at HF. I
> had a similar problem with a low-band vertical temporarily mounted about 20
> ft from my wife's computer, and by adding common-mode chokes (radio shack
> cores w/about 6 turns each) was able to run a full kilowatt without
> affecting the speakers. In some cases, you may also have to add cores at
> the computer end of the audio line also, depending on whether the RF is
> affecting the amplifiers in the speaker cases or the computer sound card
> itself (or both).
>
> Wrapping a "grounded" wire around the leads probably won't do much. What
> happens when you you grab them is that your body acts like a lossy series
> resistor and reduces the common-mode RF currents (there is "lossy-line"
> wire available commercially which has a lossy ferrite based material in the
> insulation, but it's way too expensive for amateur applications & I've never
> seen it sold in small quantities). There's also a lot of misinformation
> about "grounding" floating around. In this case, what you would want in
> terms of "grounding" is to keep all the various portions of the computer
> system at the same RF potential, which generally has very little to do with
> a connection to physical earth. Unfortunately, this probably isn't real
> practical if it's not your installation.
>
> If multiple speaker leads are physically co-located, you can reduce the
> number of cores required by wapping them all in one core.
>
> All of the above assumes that common-mode RF currents induced in the
> interconnecting wiring is the mode by which RF is getting into the
> amplifiers. This the most common coupling mode, but there is also a
> possibility that the amplifier circuit inside the speaker case is picking up
> RF directly. In this case, you would need to either modify the internal
> amplifier to be less susceptible to RF, or add shielding to the speaker
> case, neither of which is a very practical solution. Alternatively, you can
> become a QRP operator, which may not be very attractive either.
>
> Phones & TV's are also sometimes amenable to suppression of common-mode
> currents. Add telephone filters (or clamp-on ferrite cores installed as
> above) at the telephone instrument. Again, if the phone is picking up the
> RF internally there really isn't a lot you can do except offer to replace it
> with one of the models known to have good RF susceptibility characteristics
> (see list archives for previous discussions of RFI-immune phones).
>
> Depending on the coulpling mechanism, adding a choke (as many turns as will
> fit wrapped around a ferrite rod) or filter to the TV's power cord may
> help. What sometimes happens in the that TV antenna leads and the AC power
> cord act like an antenna, with the result that RF currents are forced to
> flow through the TV itself. Breaking this path with chokes or a good filter
> may help. If the mechanism is front-end overload on the TV tuner, a
> high-pass filter in the antenna lead may also help. If the mechanism is RF
> pickup by the internal wiring in the TV, you're kind of out of luck.
>
> Be very, very careful "grounding" things like a computer if the building
> wiring does not include the 3rd wire fault protection conductor. You can
> easily create a safety/fire hazard in the event of a fault. Any additional
> "grounds" need to be referenced back to the building power source ground
> with a conductor appropriately sized to provide a fault protection current
> path. Check your local electrical codes carefully, particularly if you're
> modifying someone elses equipment (the local library will have a copy). The
> same concern applies to your station, by the way....
>
> Good luck. Maybe if you have some initial success with your neighbor's
> speakers, he'll be a litte more co-operative in resolving the other
> problems.
>
> Keith
> KB6B
>
> "gm@netsync.net" wrote:
>
> > Hello,
> >
> > I wonder if I could get some advice on an RFI problem. I live in an
> > apartment that is part of a large house. There is one other apartment
> > here too, and my neighbor there has been complaing about RFI from my HF
> > rig. His main complaint is that I'm coming through the speakers on his
> > computer. My main antenna is a Butternut HF5B 2 el mini-yagi that is
> > mounted up on the roof. The bottom of the antenna is roughly 15 to 20
> > feet above his computer, and 5 feet away horizontally.
> >
> > My first question is: In the eyes of the FCC, is my antenna too close to
> > his apartment? I have heard some people say that the FCC expects a ham's
> > antenna to be at least 50 feet away from any neighbors, otherwise the
> > ham can be blamed for interference. Is there any truth to this? I
> > normally run 100 watts output, and I know that my neighbor's apartment
> > is within the FCC's RF saftey limits. I occasionally run 500 watts for
> > DX pile-ups, which is also within limits, but I only do it when the
> > neighbor is out. It's very possible that the FCC will be coming here to
> > look at the problem, so I need to know if my antenna is too close (at
> > 100w), and if I could be held responsible for the RFI problem.
> >
> > I also have dipole for 30 and 40 meters, but I only use it when the guy
> > is out. That antenna is roughly parellel to his 2nd floor apartment, and
> > about 20 feet away from it. There isn't enough room here to put up
> > anything better.
> >
> > As for cleaning up the RFI, I have not been able to do much since my
> > neighbor is not very cooperative. The problem is from HF fundamental
> > frequencies. I'm coming through the speakers on his computer, which he
> > insists on leaving on 24 hours a day. He won't turn off his amplified
> > speakers - not even before going to bed at night. He uses rabbit ears
> > for a TV antenna, and we are in a fringe reception area. His TV is at
> > least 30 feet from my antenna, and I clobber every channel. He also says
> > I come in through the phone line.
> >
> > Since his main complaint is with the computer speakers, that is where I
> > have been trying to help him so far. I don't seem to cause any
> > interference at all on his monitor. I tried using ferrite beads on
> > various speaker cables and mananged to reduce the interfence by maybe
> > 50%, but it is still very noticeable. I only had 2 beads, so I couldn't
> > do as much as I wanted, but I doubt that beads alone would have done the
> > job. He has a total of 5 speakers, with 2 separate ampifiers. At one
> > point I grabbed a hand-full of the speaker wires and the interferece
> > dropped WAY down. I'm thinking I might be able to wrap several turns of
> > wire around these cables, then ground the wire to simulate the same
> > thing. Does that make any sense? His computer is grounded btw. I
> > grounded it because the AC wiring in this place is not grounded.
> >
> > For the phone line, I will try a bead or a torroid core. For the TV,
> > I'll try a high-pass filter, but I have doubts that it will help much.
> >
> > It's been hard to do much of anything because the neighbor isn't very
> > cooperative. We agreed yesterday to work on the problem at noon today,
> > before he would go to work at 2 pm. He wouldn't answer his door or his
> > phone when I tried to reach him several times between 12 and 1:30.
> > Finally, just before he had to leave for work, he anwered his door. He
> > said he "must have been sleeping" earlier. This is typical for this this
> > guy, - it's happened before. So, I'm about ready to just go ahead and
> > operate and let him make complaints to the FCC. It's easier than dealing
> > with his lousy attitude. I need to know first though if my antenna is
> > too close to him. I'll probably be able to get in his place one last
> > time to try a few things though, so any advice on solving the RFI
> > problems is also appeciated. I've never had problems with RFI before, so
> > all of this is new to me.
> >
> > Thanks,
> > Gerry KA2MGE
> >
> > --
> > FAQ on WWW: http://www.contesting.com/FAQ/rfi
> > Submissions: rfi@contesting.com
> > Administrative requests: rfi-REQUEST@contesting.com
> > Questions: owner-rfi@contesting.com
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Message-ID: <3A43EB37.70706F71@qnet.com>
To: <rfi@contesting.com>
Date: Fri, 22 Dec 2000 16:00:55 -0800
From: blackburn <blackburn@qnet.com>
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To: rfi@contesting.com
CC: "gm@netsync.net" <gm@netsync.net>
Subject: Re: [RFI] RFI Troubles
References: <3A43D516.2720@netsync.net>
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Gerry,
A couple things. First, I've never heard of an FCC requirement regarding
antenna separation from neighbors, living spaces, etc., as long as you meet
the applicable RF exposure requirements. You can check the amateur
regulations on the web (I don't remember the address, but there's a link
somewhere on the www.fcc.gov website). There's also some good info you can
download from the ARRL website (www.arrl.org).
Computer speakers are generally pretty straightforward. Start by adding
clamp-on ferrite cores at the speakers themselves on both the audio and
power leads. Remember that you need several turns of wire through a typical
core in order to have sufficient inductance to have much effect at HF. I
had a similar problem with a low-band vertical temporarily mounted about 20
ft from my wife's computer, and by adding common-mode chokes (radio shack
cores w/about 6 turns each) was able to run a full kilowatt without
affecting the speakers. In some cases, you may also have to add cores at
the computer end of the audio line also, depending on whether the RF is
affecting the amplifiers in the speaker cases or the computer sound card
itself (or both).
Wrapping a "grounded" wire around the leads probably won't do much. What
happens when you you grab them is that your body acts like a lossy series
resistor and reduces the common-mode RF currents (there is "lossy-line"
wire available commercially which has a lossy ferrite based material in the
insulation, but it's way too expensive for amateur applications & I've never
seen it sold in small quantities). There's also a lot of misinformation
about "grounding" floating around. In this case, what you would want in
terms of "grounding" is to keep all the various portions of the computer
system at the same RF potential, which generally has very little to do with
a connection to physical earth. Unfortunately, this probably isn't real
practical if it's not your installation.
If multiple speaker leads are physically co-located, you can reduce the
number of cores required by wapping them all in one core.
All of the above assumes that common-mode RF currents induced in the
interconnecting wiring is the mode by which RF is getting into the
amplifiers. This the most common coupling mode, but there is also a
possibility that the amplifier circuit inside the speaker case is picking up
RF directly. In this case, you would need to either modify the internal
amplifier to be less susceptible to RF, or add shielding to the speaker
case, neither of which is a very practical solution. Alternatively, you can
become a QRP operator, which may not be very attractive either.
Phones & TV's are also sometimes amenable to suppression of common-mode
currents. Add telephone filters (or clamp-on ferrite cores installed as
above) at the telephone instrument. Again, if the phone is picking up the
RF internally there really isn't a lot you can do except offer to replace it
with one of the models known to have good RF susceptibility characteristics
(see list archives for previous discussions of RFI-immune phones).
Depending on the coulpling mechanism, adding a choke (as many turns as will
fit wrapped around a ferrite rod) or filter to the TV's power cord may
help. What sometimes happens in the that TV antenna leads and the AC power
cord act like an antenna, with the result that RF currents are forced to
flow through the TV itself. Breaking this path with chokes or a good filter
may help. If the mechanism is front-end overload on the TV tuner, a
high-pass filter in the antenna lead may also help. If the mechanism is RF
pickup by the internal wiring in the TV, you're kind of out of luck.
Be very, very careful "grounding" things like a computer if the building
wiring does not include the 3rd wire fault protection conductor. You can
easily create a safety/fire hazard in the event of a fault. Any additional
"grounds" need to be referenced back to the building power source ground
with a conductor appropriately sized to provide a fault protection current
path. Check your local electrical codes carefully, particularly if you're
modifying someone elses equipment (the local library will have a copy). The
same concern applies to your station, by the way....
Good luck. Maybe if you have some initial success with your neighbor's
speakers, he'll be a litte more co-operative in resolving the other
problems.
Keith
KB6B
"gm@netsync.net" wrote:
> Hello,
>
> I wonder if I could get some advice on an RFI problem. I live in an
> apartment that is part of a large house. There is one other apartment
> here too, and my neighbor there has been complaing about RFI from my HF
> rig. His main complaint is that I'm coming through the speakers on his
> computer. My main antenna is a Butternut HF5B 2 el mini-yagi that is
> mounted up on the roof. The bottom of the antenna is roughly 15 to 20
> feet above his computer, and 5 feet away horizontally.
>
> My first question is: In the eyes of the FCC, is my antenna too close to
> his apartment? I have heard some people say that the FCC expects a ham's
> antenna to be at least 50 feet away from any neighbors, otherwise the
> ham can be blamed for interference. Is there any truth to this? I
> normally run 100 watts output, and I know that my neighbor's apartment
> is within the FCC's RF saftey limits. I occasionally run 500 watts for
> DX pile-ups, which is also within limits, but I only do it when the
> neighbor is out. It's very possible that the FCC will be coming here to
> look at the problem, so I need to know if my antenna is too close (at
> 100w), and if I could be held responsible for the RFI problem.
>
> I also have dipole for 30 and 40 meters, but I only use it when the guy
> is out. That antenna is roughly parellel to his 2nd floor apartment, and
> about 20 feet away from it. There isn't enough room here to put up
> anything better.
>
> As for cleaning up the RFI, I have not been able to do much since my
> neighbor is not very cooperative. The problem is from HF fundamental
> frequencies. I'm coming through the speakers on his computer, which he
> insists on leaving on 24 hours a day. He won't turn off his amplified
> speakers - not even before going to bed at night. He uses rabbit ears
> for a TV antenna, and we are in a fringe reception area. His TV is at
> least 30 feet from my antenna, and I clobber every channel. He also says
> I come in through the phone line.
>
> Since his main complaint is with the computer speakers, that is where I
> have been trying to help him so far. I don't seem to cause any
> interference at all on his monitor. I tried using ferrite beads on
> various speaker cables and mananged to reduce the interfence by maybe
> 50%, but it is still very noticeable. I only had 2 beads, so I couldn't
> do as much as I wanted, but I doubt that beads alone would have done the
> job. He has a total of 5 speakers, with 2 separate ampifiers. At one
> point I grabbed a hand-full of the speaker wires and the interferece
> dropped WAY down. I'm thinking I might be able to wrap several turns of
> wire around these cables, then ground the wire to simulate the same
> thing. Does that make any sense? His computer is grounded btw. I
> grounded it because the AC wiring in this place is not grounded.
>
> For the phone line, I will try a bead or a torroid core. For the TV,
> I'll try a high-pass filter, but I have doubts that it will help much.
>
> It's been hard to do much of anything because the neighbor isn't very
> cooperative. We agreed yesterday to work on the problem at noon today,
> before he would go to work at 2 pm. He wouldn't answer his door or his
> phone when I tried to reach him several times between 12 and 1:30.
> Finally, just before he had to leave for work, he anwered his door. He
> said he "must have been sleeping" earlier. This is typical for this this
> guy, - it's happened before. So, I'm about ready to just go ahead and
> operate and let him make complaints to the FCC. It's easier than dealing
> with his lousy attitude. I need to know first though if my antenna is
> too close to him. I'll probably be able to get in his place one last
> time to try a few things though, so any advice on solving the RFI
> problems is also appeciated. I've never had problems with RFI before, so
> all of this is new to me.
>
> Thanks,
> Gerry KA2MGE
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/rfi
> Submissions: rfi@contesting.com
> Administrative requests: rfi-REQUEST@contesting.com
> Questions: owner-rfi@contesting.com
--------------F8ABB40278746BF86F181EC4--
--
FAQ on WWW: http://www.contesting.com/FAQ/rfi
Submissions: rfi@contesting.com
Administrative requests: rfi-REQUEST@contesting.com
Questions: owner-rfi@contesting.com
|