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Click on the picture for RFI filter construction.
I have very bad telephone RFI caused by a amateur (HAM) radio.
I have tried the following, k-com rfi-1, at&t z100b1, at&t m-150, at&t
m-150h (these are plug ins on the phone) the following were installed by
the phone co. on the wireing into the house, listeo 4885, a40ba,and two
other filters without numbers. Nothing works and they tell me they dont
have any other filters and haven't any other ideas.
Meanwhile I still
have the RFI problem with my phones and worst yet with the neighbors
Do you think your rfi killer RFI-1 will work and will you take
it back if it won't( I will pay the shipping back).
I get the RFI running my radio with 50 watts or with the linear amp
on with 600 watts. I am lookin forward to hearing from you.
Thanks for the inquiry. I'm surprised that the filters that you tried at
the phone didn't at least reduce the interference.
Our filters work
anywhere from 4 to 5 times better, depending on the frequency, than
To effectively evaluate a filter you should disconnect all other
equipment connected to the line and try the filter on one phone at a
The filter should be as close to the phone as possible and if it
works there, you could then try it at the wall connection bearing in
mind that any length of wire between the filter and the telephone can
act as an antenna also.
I have had cases were the audio was being rectified (ie. changed from
radio frequency to audio frequency) by a corroded or loose screw
terminal connector and a crank in the right spot with a screwdriver
solved the problem (especially out in the entry box). If rectification
has taken place a filter will not help. In other situations the
rectification has been traced to a faulty lightening arrestor at the
telephone line service entrance.
Recently we have improved the performance of our plug-in filters and
they work just as well as the RFI-1.
Sure, if the filter does not solve
your problem you can return it for a complete refund. Let me know if you
want to try a modular filter (it should first be tried on one telephone
at the phone end of any wiring with all other equipment disconnected
from the phone line. If it does not help, I would suspect rectification.
What bands do you mostly operate?????
Awaiting your reply
John K. Browne
I got your reply and thank you. Please let me explain a little more
about the telephone RFI problem I have.
I get into my own phones, but I
can live with this....the real problem is me getting into the neighbor's
phones. They have called the phone company several times and the phone
company has really been very good to me by putting several filters on
the lines coming into our house and on the neighbor's houses too. So far
nothing has worked and the last time they were here they told me that
they don't have any more things to try. I am assuming they will not be
back again even if the neighbors call them and who knows what will
happen next. I have tried unplugging the phones and putting one back at
a time. It doesn't make any difference.
Have tried several filters. I
use the best coax and connectors, even drilled a hole into my basement
floor and grounded the ham radio and all other equipment three feet
away. I get into the phones if I use 50 watts or 600 watts. Will order
one of your filters. Sure hope it works.
Your problem intrigues me somewhat since it has been so hard to fix.
What I have been trying to say is that if you can fix your own telephone
system and understand the solution somewhat, then you will have much
better luck in helping the neighbors solve their problems.
Do you get the telephone RFI on 40 mtrs and 80 mtrs as well as
First of all, establish what the minimum power level is that you need to
generate the RFI and troubleshoot the problem first at this reduced
power level rather than try to initially solve the problem at say a
kilowatt SSB on 20 mtrs.
I would prefer that you try our filter on 40 mtrs or 75 mtrs first also
as they have much superior performance at those frequencies even though
they work very well on 20 mtrs.
Disconnect all the things connected to your telephone line (don't forget
the cords as well as the equipment itself (ie. alarm systems, unused
cords, fax machines, telephones, computers etc.) and try the filter on
one or two different phones one at a time.
If the interference is still there, try connecting a K-COM filter in series with
our filter (they should just plug into each other). Also for this test,
make sure you are not using a telephone that is ac powered. If the
interference is still there with 2 or more filters in series, then you
most likely have RF rectification taking place somewhere in your
Make sure the telephone wiring is the standard telephone "twisted pair"
wire, not parallel pairs or coax.
Go through the whole system from wall outlets to service entrance inlet box and tighten up all the screw connectors. Look for corroded or loose
connections. If you have a bundle of different pairs, unused pairs
should be grounded if possible. If you still think it is rectification
and none of the tightening works then have the telephone people check or
replace the telephone system lightening arrestor.
If you still get RFI with the telephone unplugged from the wall but
still connected to it's cord unplug the cord from the phone completely.
If the interference is gone then a filter plugged into the phone (at the
phone, not the wall end of the cord) should solve the problem. If the
interference is still there, then you should try a different phone or
locate your antenna farther away or higher.
It sounds like you may have a number of possible situations with the RFI.
You may be in a very strong RF field.
Where is the antenna, in relation to your house? How far away is it????
What kind(s) of antenna's are you using?????
I have found that a low angle radiator especially a vertical low angle
radiator really puts a nice lobe(s) at ground level right through the
phone wiring and neighbors houses.
For reducing the local ground level field strength, I have had much
better luck with a simple single band coax fed dipole (even in a v
A friend of mine who lived in a single story house with a vertical
groundplane antenna in the center of his roof, had telephone
interference problems on his own phone.
It was so bad that filters did
The RF field was so strong that the telephone still picked up
the RFI even when it was completely disconnected from the wall jack.
finally was persuaded to convert a couple of radials into halves of a
dipole and move it off the house.
He still had telephone RFI but it was
reduced enough for a filter to remove the problem while he enjoyed daytime
40 mtr ragchewing
(A dipole at 20 ft. works very well for 500 mile
radius daytime activity on 7 Mhz ).
The other possibility is RF rectification.
Here's an experiment:
Take a set of high impedence communication type headphones. wire up a
headphone jack with an RF choke in each side of the headphone wire going to a set
of wire test leads (junkbox RF chokes in the range of 1 mH. do an
excellent job). You should also put approx. one microfarad in series with each side of
the headphones and the line, to isolate the phones from the D.C. level present. Connect the
phones up before you put them on your ears because the D.C. will
probably produce a loud click upon connection.
Plug in the headphones (keep the cord wound up into a small area to
avoid RF pick-up), connect the test leads to each side of the telephone
wiring and listen. If it is RF, you should not hear any interference.
If it has already been rectified (ie. changed to an audio frequency) you
should hear the interference. This would be one way to tell if you have
a rectification problem.
What do you think sir???
Hi John I got your filter today and it works better than any I have
tried before. A friend and I did the test with the earphones and we
didn't hear anything, so I must have a RF problem. I have a Yaesu
FT-1000 that will put out 200 watts and at this range with your filter
inline there isn't any interferance. With the amp on (600 watts) there
is interferance but not as bad and if I put a K-COM in line also it will
cut it down to a level that would alow you to use the phone. The K-COM
alone is useless, not anywhere as good as yours. I would like to know if
I use another one of your filters in line with the other one if that
would get rid of the interferance completly? I would also like to know
if you could or would make me a filter that has more windings and let me
expermint with it. They say bigger is better and I sure would like to
try something bigger. Please e-mail me back and let me know what you
think of this idea.
Thank you very much
Two filters should really do the job. (you can add as many as you
need because that don't add any appreciable resistance to the line.
Since your neighbors are at a little further away, it might take only
one filter to solve the problem at their QTH.
What frequency were you on when you tested the filter??(just curious).
I have experimented with different cores and windings and this
configuration seems to be the best. There is a point of diminishing
returns with more windings (the interwinding capacitance comes into play
and starts to reduce the filtering effect). Adding more windings lowers
the frequency range of the filter and I think I have it positioned to
cover the am broadcast band as well as HF and some vhf, right now.
Also we already have about as many turns as you can cram onto this size
ferrite bead and still maintain some isolation distance between the
input and output ends of the winding.
I have tried various size beads and in general the larger beads work
better at lower frequencies and smaller beads work better at higher
The best way to dramatically increase the RF attenuation is to use more
than one filter.>BR>
I tried the filter at a neighbor's house and it works until I turn
the amp on, then I get into their phone with the same amount of
interference as mine. I put the K-Com on but it didnt do much good. I
would like to try another of your filters to see if it will work any
I dont have any trouble with 40m or 80m because they are on a full
wave loop, that is away from the house in a neighbors field. my trouble
is with 20m, 15m and 10m, do you or is there a way you can make a filter
for these bands.
My antenna is located about three feet from the rear of the house.
this is about 50 feet from where the phone wires enter the house. The
tower is a 50ft aluminum, the antenna is a force 12 c4xl yagi. There are
seven elements which covers 20m thru 10m and 12m-17m with the ant
tunner, this is fed with a single feed line of coax. There is also 2
elements for 40m and this is fed with another single line of coax.
considering adding another 20ft or 30ft to the tower because I am told
that this will change the lobe pattern of the antenna. This will give me
better than a 50-50 percent of getting out of the phones all together,
DO YOU THINK IT WILL?
There are no traps on the antenna and the 40m is
linear loaded (no traps).
I use 20m abt-60%, 15m thru 10m-40% and 80m
and 40m-10%, so you see I really need a filter for 20m thru 10m.
Again if you do or can make a filter for my needs please do, I really
do APPRECIATE all of your help.
I went through and tested about 50 filters today. There is a slight
difference in performance due to choke orientation and spacing as well
as slight variation in the actual choke windings. I selected out the 2
best ones for 20 mtrs. (they each have more attenuation than the K-KOM filter
at 14 Mhz).
I will send them both to you for a trial. Try them hooked together and
think of it as a super 20 mtr filter. If that works well, you might try
them one at a time. I am not sure how they compare with the one you
already have as I did not specifically select that one for 14 Mhz.
If you think you need them both, I could probably give you a slight
break on the price.
There is one other way to dramatically increase the performance of these
filters on most frequencies.
In situations where you have a chassis close by, such as the computer
chassis near the modem connection, placing the filter on the grounded
metal chassis will increase the attenuation approx. 3 times. The side of
the filter opposite the lid should be up against the chassis. You can
use double sided sticky foam tape available at Radio Shack to stick the
filter against the back of the computer near the modem.
In other situations where a ground is available close by, you can solder
a short ground wire to a rectangular piece of copper or tin etc, (make
the rectangle just a little smaller than than the filters length and
height) and then tape the rectangle to the correct side of the filter
with plastic electricians tape. Ground the wire and it will improve
filter performance. This has the effect of adding a pypass capacitor to
the internal chokes.
Yes, raising the antenna up higher should definitely help. Just the
extra distance will reduce the field with the square of the distance
(inverse square law).
I'm presently working on an even better filter configuration for 10,15 and 20
mtrs. I'm not sure how long it will take me to get the attenuation that
Anyway here it is Friday again. I will put the filters in the mail asap.
Let me know how they work out.
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