[RFI] Telephone Interference - blowing out phones?
Dana Roode <K6NR@ARRL.net>
Sun, 02 Jan 2000 14:19:45 -0800
Let me update you about the problem I reported below. First off, I
would like to thank all of you who responded to my e-mail, I've not
had a chance to reply to each of you. I received about 20 replies
with all sorts of useful information, suggestions, and moral support.
This list is a great resource. I will not need to resort to QRP.
I responded to my neighbor's angry letter in a very diplomatic
fashion, ignoring the threats, and concentrating on the issue at
hand. I explained the situation to her, noting that it was a
"technical problem, not a legal problem" (quote from one of the RFI
write-ups), and pointed her to the URL for the FCC phone RFI bulletin:
This is a great document that spells out the situation for the
consumer. Its particularly important since it comes from the FCC and
not me or some Ham organization. I closed my letter to my neighbor
with an offer to help, if she was willing to work with me (without the
My neighbor responded in a positive fashion, I asked her some
questions, and setup a time to help debug the situation. The phones
involved were the wired variety, she had given up on cordless earlier
because of interference from me. The fix I gave her for TVI last
March was working fine. The telephone interference wasn't literally
constant, it was a weekend/evening thing, fitting my operating
I did my homework, read the ARRL RFI Book chapter on phone RFI (the
ARRL's book is *very* helpful), read other write-ups on the Web, and
all of your e-mail. I ordered a "bullet-proof" phone from
Pro-distributors in Texas - I planned to leave it with my neighbor if
necessary and use it as a "debug" device otherwise. I also got a $20
RadioShack 43-591 phone, which you folks thought was good in RFI
situations. I got plenty of FT140-43 toroids from Amidon (they are a
few miles away), and a couple of K-Com phone filters.
I arranged a time for my brother, KA6CCF, to key the rig while I was
at my neighbor's house. Wow, her GE wall-phone heard me on every
band, even without the Amp. In fact, her phone picked up the small
FRS walkie-talkie I was coordinating with my brother on too. These
phones are great receivers. I tried the RFI phone - problem was gone,
indicating there was no audio rectification elsewhere on the line. I
tried her phone connected through a cord over 9 turns on a FT140-43 -
problem solved. I didn't even need a K-COM filter.
When my brother transmitted on 10 meters, I could hear a thunderous
sound echoing throughout my neighbor's house. No wonder she was
angered after my 10 meter contest weekend. Her son's stero was the
culprit, eventhough it was turned off. A FT140-43 on the stereo side
of each speaker lead solved the problem.
I told her to log further problems - date, time, severity - so I could
figure out frequency, reproduce and resolve them. In the end, my
neighbor was very appreciative, and didn't attribute the problem to
me. I think the FCC document was key in putting things in perspective
for both of us.
Thanks to everyone for your help and advice. Now, on to solve my
power line noise problem, which has made the radio fairly useless over
the past few weeks.
PS: Can 400w from an antenna 30 feet away blow out a phone? Most
folks, including me, thought not. Ed Hare did a quick computer model
of the situation, and from his information I came away thinking it was
possible after all. And, my neighbor had no reason to make it up (she
never asked me to pay for any broken phones).
Dana Roode wrote:
> [Originally written 12/13/99, second try at posting]
> Hi all,
> I've been a ham for 30 years and have only been involved in a few
> interference situations. Unfortunately, I've got one now, and I'd
> like your input and ideas.
> I've lived at my present location for about 11 years, without any
> interference complaints (other than a odd burglar alarm case from a
> house a block away). There have been three different neighbors in the
> house next door - the first two had no complaints, but the current one
> does. I received a letter from her today, after thinking things were
> OK after a conversation and a visit several months ago. At that time
> the main complaint was with regard to her TV, I found a poor cable
> connection, and added a toroid on the cable. She doesn't mention TVI
> in the letter, so maybe I made some progress there.
> She has several complaints, but the most serious appears to be with
> regards to her telephone. She says that there is constant
> interference on her phone lines, completely disrupting conversations.
> She claims that "at least three phones have been blown out in the past
> year". I don't yet know what kind of phones she means, but I will be
> asking. I had previously given her a filter for her phone, and she
> says that she has contacted the phone company and paid to have filters
> installed, all to no avail.
> I was on 10 meters this weekend, running 400w into my vertical on my
> roof, base at about 30'. No interference to my phones or anything
> else in my house. My neighbor's house is 10 feet away from mine,
> about 30' from my vertical. My equipment is grounded to a set of 8'
> copper grounding rods right outside the window; I run with a low pass
> filter. (I'm wondering if those transmitting common mode chokes are
> necessary or helpful, since I don't use one).
> Anyone ever hear of phones being blown out due to RFI? If the phone
> company has installed filters, what's left to try in resolving the
> When I last spoke with her, she said she had problems with both
> cordless and wired phones. What are folks experiences with cordless
> phones? Are the current variety pretty sensitive to nearby
> transmitters? We have a 49mhz cordless, but don't use it enough to
> know if it works when I'm transmitting.
> Are there professionals out there that deal with cases like these?
> What's the best way to get good help from the phone company?
> Any input on any of this will be appreciated. Meanwhile, QRP is
> looking better all the time,
> Dana Roode
> Irvine, California
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