[RFI] NOISE GADGETS
David Jordan
wa3gin at erols.com
Wed Nov 10 13:52:54 EST 2004
1st, go the the NIC and determine if the RFI is coming in from the
outside phone plant. If yes see note (A) below.
(A) A common surplus AC brute force line filter will do a splendid job
of removing RF from your house phone lines. Place the line side towards
the NIC and the load side towards the phone instrument/s. Ground the
metal case.
2nd, if RFI is not originating from the outside plant, take precautions
as noted in (A) and add additional filters at the telephone jack/s
which feed the phone instrument which is experiencing the RFI.
Have Fun,
dave
wa3gin
dgsvetan at rockwellcollins.com wrote:
>Jim and Howard,
>
>A couple of things I'd like to mention relative to twisted pairs:
>
>1. Twisted pairs are most effective at minimizing common mode effects at
>low frequencies. Ma Bell (remember her?) used 600 ohm twisted pairs for
>the station wiring for a very long time. 'Real" telephone wire IS made of
>twisted pairs. The twisting is why you can hear the person on the other
>end, and not 60Hz hum. However, the twisting will not prevent the coupling
>of RF into the telephone device. The RF arrives equally on all wires
>within the cable jacket and couples very nicely thru the stray cap of any
>hybrid transformers or active coupling devices used to interface the
>telephone line. Ferrites applied to the phone line, as close to the
>telephone instrument itself as possible, will reduce or eliminate RFI to
>telephones IF it introduces enough loss/series impedance at the RF
>frequency. Again, from numerous prior posts, don't expect the Radio Shack
>ferrites to help you keep lots of HF RF out of your phone.
>
>2. Howard - what sort of wire do you have for your in-house phones?
>Unless the builder ran "speaker wire", I would guess that he really did run
>twisted pair. This is especially true if you do not have a lot of hum on
>your phones. Note that the twists for telephone wire are not given in
>twists per inch, but in twists per foot. Therefore, you have to expose a
>foot or two of the wire (remove outer cable jacket) to see if the conductor
>pairs are twisted. What colors are the wires? Station wire cable will
>have RED, GREEN, YELLOW, and BLACK conductors, with the pairing being R/G
>and B/Y. Actual multiple pair telephone cable will have a BLUE/BLU-WHT
>pair as pair #1, followed by ORG/ORG-WHT as pair #2. It sounds like your
>builder probably had some sort of deal with the electrician and/or telecom
>provider in not letting you or your friend do wiring. Luckily, my wife
>and I were able to put in sweat equity on our house a few years ago by
>letting the electrician do all the 120/240 stuff and us doing all of the
>telecom stuff (telephone, intercom, Cat 5E for LAN, A-V distribution, etc).
>
>3. Jim, yes, it is possible that you might have some of the old carbon
>pile "protectors" on your phone lines. I believe that if corrosion sets in
>on those things, you might get RFI effects from the galvanic detector
>action within the corroded areas. A good visual inspection might be in
>order. On the other hand, I am convinced that, with few exceptions, most
>of the available consumer telephones today are junk as far as RF
>susceptibility. If you look back in the archives of the reflector over the
>past two or three years, there were some postings about a particular model
>of Radio Snack phone that was pretty close to bullet-proof. The best
>phones for RF rejection are the original 500-type sets from WECo and ITT
>Kellogg. If you have them, or find them, keep 'em and use 'em!
>
>That said, let me relate the following:
>
>My last job back in the Chicago area was at Lindgren RF Enclosures (now
>ETS-Lindgren), located in Glendale Heights. The company's building was
>located in an industrial park that was directly adjacent to 50 kW AM radio
>station WMAQ, at 670 kHz. I estimated that our building was about 1500 to
>2000 feet from the base of 'MAQ's tower. I took some rough spectrum
>analyzer measurements, and it appeared that the steel and concrete
>structure of the building was worth about 40 to 50 dB attentuation,
>relative to the 670 kHz signal just outside the walls. Amazingly, there
>were no phone system problems within the building. Now, also adjacent to
>the WMAQ tower area (around the corner from the industrial park) was an
>apartment complex, built with frame construction. Over time, a few
>Lindgren employees did live in that complex. Some of them came to me with
>complaints that they could not use their home telephone because of WMAQ's
>signal. Luckily for them, I had a stash of ferrites that I had gotten from
>Lindgren's Elmag filter division (now, no longer in business) that were
>used in certain facility filters. These ferrites were about 2 inches long
>by 5/8 inch diameter with a roughly 1/4 inch hole thru the center. I
>suggested that they take the ferrite home, unwire the phone from the line
>connection, pass the line thru the ferrite as many times as possible, and
>then reconnect. I also advised them to use as short of a cord as possible
>between the phone body and the handset. As far as I know, it worked every
>time. Problem: I never did get the specs on that ferrite!
>
>Best wishes with your projects.
>
>73, Dale
>WA9ENA
>
>
>
>
>
>
>
>
> "Jim Brown"
> <jim at audiosystems To: "RFI List" <rfi at contesting.com>
> group.com> cc:
> Sent by: Subject: Re: [RFI] NOISE GADGETS
> rfi-bounces at conte
> sting.com
>
>
> 11/09/2004 06:27
> PM
> Please respond to
> Jim Brown
>
>
>
>
>
>
>On Tue, 9 Nov 2004 16:10:38 -0700, Howard Lester wrote:
>
>
>
>>Thank you!
>>
>>One 'quick' question: just how beefy do the speaker cables need to be to
>>
>>
>get
>
>
>>good, solid bass? (I will go to the site to read the articles.) I am not
>>
>>
>yet
>
>
>>aware of, say, 14 gauge twisted pair wire - shame on me, I guess.
>>
>>
>
>West Penn, Gepco, and Belden all make stranded twisted pair cable in the
>#12 - #14
>gauge range. You can also "roll your own" out of stranded THHN from Home
>Depot by
>sticking it in a twist drill. And you can "double up" on pairs of
>instrumentation cable.
>
>
>
>>I have known for a long time about twisted pair helping to reject RFI.
>>
>>
>Tell
>
>
>>that to the homebuilders; they seem to refuse to use it for telephone
>>wiring, even though it is allegedly "code."
>>
>>
>
>Don't know about the "code" part, but CAT5 and similar cables make
>EXCELLENT
>telephone wiring. For one thing, they have very low capacitance, so they
>will help a bit
>with data transmission.
>
>
>
>>I had a ham friend who offered
>>to do the wiring of my new home with correct telephone cable. Even though
>>she worked for the phone company, my builder refused to allow her on the
>>premises. If I wanted twisted pair, I would have had to pay a premium. I
>>said screw it -- it's only my house, and I'm the only ham around. No one
>>around (also with 'bad' wiring) has complained about my 100 watt station.
>>
>>
>
>One of the last instances of RFI that I'm chasing with my KW station (and
>antennas quite
>close to the house) is into my wife's telephone. I've got a bunch of
>ferrites on the wiring,
>but it's still getting in. I'm starting to wonder if maybe it isn't
>rectifying in some of the
>ancient telco termination gear in my basement. I haven't shifted all my
>telco stuff to
>CAT5 yet, but I probably should.
>
>Jim
>
>
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