Radio Frequency Interference Solutions

Click on the picture for RFI filter construction.

John: 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 phones.
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.

Joe:
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 K-COM.
To effectively evaluate a filter you should disconnect all other equipment connected to the line and try the filter on one phone at a time.
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

John:
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.
Joe

Joe'
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 20mtrs???????

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 telephone wiring.

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 config.).

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 not help.
The RF field was so strong that the telephone still picked up the RFI even when it was completely disconnected from the wall jack.
He 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???
73.......de......KI6KY.......sk John

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

Joe,
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 frequencies.

The best way to dramatically increase the RF attenuation is to use more than one filter.>BR>
Sincerely,
John Browne

John:
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 better.
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.
I am 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. Thank You

Joe:
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 I want.
Anyway here it is Friday again. I will put the filters in the mail asap. Let me know how they work out.

73........de......KI6KY

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