[RFI] Re: rfi-digest V1 #42
Cortland Richmond
Cortland Richmond" <cortland_richmond@qmgate.optilink.dsccc.com
24 Mar 1998 09:35:24 -0800
RE>rfi-digest V1 #42 3/24/98
Ed, K0il, writes
>>...The 2 inch long ferrite clamp on "beads" sold by radio shack are about $3 or $4 each. I used about 25 of them on the Stereo and 10 more on the leads from the computer to mouse and keyboard and monitor."
These ferrites are usually not very effective at low frequencies. Just as a rule of thumb, I'd count on 50 to 100 ohms at 100 MHz and about ZERO ohms at 10 MHz for one pass of wire through the core.
Where this many were needed, it is likely the same result could have been obtained by top-quality shielded cables, adding grounding clips inside the computer, or adding additional shield over the existing cables, or combinations of these measures. 25 ferrites is a LOT of money, especially at Radio Shack's retail price.
Cortland, KA5S
--------------------------------------
Date: 3/23/98 20:49
To: Cortland Richmond
From: rfi@contesting.com
rfi-digest Monday, March 23 1998 Volume 01 : Number 042
In this issue:
Re: [RFI] Television RFI
[RFI] Re: Computer noise and other RFI problems
[RFI] Television RFI
[RFI] Telephone RFI
See the end of the digest for information about na-user-digest
----------------------------------------------------------------------
Date: Mon, 23 Mar 1998 08:57:30 -0600
From: "k0il@qsl.net" <EEDWARDS@oppd.com>
Subject: Re: [RFI] Television RFI
>When my tv is off, I receive spikes on my HF receiver spaced about
>54kHz apart (switching power supply?). They are typically about S9.
>When the tv is turned on, the spikes turn into broadband noise typically
>around S4 to S5.
I have a similar problem with my Sony XBR trinitron TV, but only while it is
on. I am lucky that it is quiet when it is turned off! It's mainly
bothersome on 17 & 15 meters. In addition to generating RFI, it rcvs RFI
quite well too!
The XBR is a fine TV except for the cheap power supply. I've had two fail on
me, and they generate more & more noise until they fail. I also tried
wrapping everything into & out of the TV. It helped on the RFI into the TV,
but not at all on the noise coming out of it.
I also considered getting an ANC-4, but have decided to what until I get my
tower up this summer to see if having the ham antenna further away from the TV
helps. I use an R5 vertical on the roof directly above the TV now.
73,
de ed -- K0iL
k0il@qsl.net
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------------------------------
Date: Mon, 23 Mar 1998 09:51:21 -0600
From: "Wendell Wyly" <w5fl@flash.net>
Subject: [RFI] Re: Computer noise and other RFI problems
No, DX4WIN is not the place to post RFI stuff. I did not see your question
on the rfi reflector.
Radio Shack sells a pretty good RFI filter for phones. I bough my neighbor
one and installed one on my phone and then bought the Radio Shack 43-585B
phone. The filter cost $20 or you can buy the 43-585B phone that is RFI
"proof" for $20. Both work well and both are recommended by the ARRL list
of RFI devices that they have tested.
Most problems with my computers have been through the keyboard and mouse or
monitor signal or power cord. The 2 inch long ferrite clamp on "beads" sold
by radio shack are about $3 or $4 each. I used about 25 of them on the
Stereo and 10 more on the leads from the computer to mouse and keyboard and
monitor. Also put in better grounding for the transmitter. Worked for me.
The problem in my case was that the equipment (computer) was not (never)
certified to FCC Class B as it is required by law to be. I recently bought
a 17 inch monitor and made sure it met European Standards for radiation
(CE). It is Mitsubishi Diamond Pro 87TXM and is MUCH quiter than my old
monitor. No RFI problems with it with KW and 2 element quad 30 feet from
shack. My computer case and the Metal ISOTEL surege suppressor are also
well grounded as is the printer.
I have no RFI of any kind with my TV and Component Stereo on any band with 1
KW. The ferrite clamp on "beads" work well, unfortunately you need a bunch
of them.
Also used 2 of them on the wiring to the photoelectric eyes and manual push
button (at the control box) to the garage door opener. Before that my wife
said she could hear me sending code through the garage door opener. It
works perfectly now.
Wendell Wyly W5FL w5fl@flash.net
(A real 5 located near Weatherford Texas)
- -----Original Message-----
From: Pete Smith <n4zr@contesting.com>
To: dx4win@qth.net <dx4win@qth.net>
Date: Monday, March 23, 1998 5:25 AM
Subject: RE: Computer noise
>At 06:50 PM 3/21/98 -0800, you wrote:
>>Gents
>>Friend of mine was having similar QRN from his computer. No amount of
>>toroids on the cords helped, nor did grounding.
>>
>>What finally cured it was to install a filter-type plug in the computer
>>power supply. These are widely available at your electronic supply,
Mouser,
>>Allied, etc. Pain in the neck but it worked for him.
>
>Not quite the same question, but an allied one -- I've posted it to he RFI
>reflector at contesting.com but got no response (no messages at all) in a
>week.
>
>After two years with no RFI problems, my wife got a new computer and I'm
>bothering it. Nothing terribly dramatic, but enough monitor flicker to be
>very annoying. Just starting the pursuit of solutions, but my suspicion is
>that it's coming into her computer on the power or phone lines, because my
>antennas are 200 feet from the house so direct pickup through the computer
>or monitor case seems less likely. I think I know how to handle the phone
>line, if that's the issue, but what do people recommend as a line filter?
>My last one was 30 years ago!
>
>
>
>73, Pete Smith N4ZR
>n4zr@contesting.com
>
>"That's WEST Virginia. Thanks and 73"
>
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------------------------------
Date: Mon, 23 Mar 1998 18:32:44 -0500
From: JACK ALTHOUSE <Palomar@compuserve.com>
Subject: [RFI] Television RFI
>When my TV is off, I receive spikes on my HF receiver spaced about 54 kHz
apart (switching power supply?). They are typically about S9.
>When the TV is turned on, the spikes turn into broadband noise typically
around S4 to S5.
First find the exact path the RFI is taking. To check the TV power cable
with Radio Shack "clamp-on" core you must make 5 turns or so on the core to
be effective. If no change disconnect the antenna cable. If RFI disappears
treat the cable with ferrite. Check anything else connected to the TV.
If no change then the path is direct radiation from the TV. Shielding
required. A coax cable from your receiver terminated in a small one turn
wire loop can snoop (cautiously) around the TV chassis to find the source.
Apply shielding to that area (cautiously and non-shorting).
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------------------------------
Date: Mon, 23 Mar 1998 21:43:01 -0600
From: Samuel Macy <sammac@interaccess.com>
Subject: [RFI] Telephone RFI
Has anyone successfully reduced RFI by shunting a .001 or .002 mfd
capacitor across a phone line? Sam
Samuel C. Macy W2DNN
486 Glenwood Trail
Elgin, Illinois 60120
(847)695-0218
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------------------------------
End of rfi-digest V1 #42
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