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AM radio on telephone

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wolf9545

New Member
I live in an apartment building about 1/2 mile away from a AM radio station. I have the Verizon FiOS service for my land-line phones. Because I live on the third floor the copper has to travel from our phone, down to the 1st floor to the punch down block, then back up to the FiOS box. So sometimes we get the AM radio station coming through the phone. The phones are a AT&T DECT 6.0 cordless phones but I also get the radio station to come through a corded phone.

I did call Verizon and they gave me a little "RF filter" to plug in between the phone and the wall. The radio can be overhead at different times of the and in different locations in the apartment. When I can hear it, it doesn't matter where I stand in the apartment.

What I am wondering is if there is a circuit that I can build that I can plug in between the phone and the wall that I can adjust to remove the RF interference?
 

Boncuk

New Member
It's not you who has to take care of minimizing radio interference, it's the company operating the radio station.

Make a complaint at your local police station and they will proceed with the rules.

Boncuk
 

wolf9545

New Member
I will give that a shot but when I had Verizon over they said that there is not much that they (verizon) could do about it because of the close proximity to the radio station & the power of the station. I also believe that having a phone line that travels up / down three floors doesn't help since it acts like a big antenna.
 

RadioRon

Well-Known Member
It's not you who has to take care of minimizing radio interference, it's the company operating the radio station.

Make a complaint at your local police station and they will proceed with the rules.

Boncuk

I must strongly disagree. Both the law and accepted convention takes the viewpoint that radio broadcasting is very valuable and so it gets protection and preference by law. It is the electronic gadget that is suffering the overload interference that must cope with the radio station, not the other way around.

It is safe to say that makers of consumer electronics equipment tend to design their devices for only so much protection from interference, enough to deal with the majority of circumstances. The OP is, unfortunately, not within that majority and now has to deal with this problem himself.

I mentioned the term "overload interference" because this is the most likely kind that the OP is suffering. The other kind might be spurious signals and perhaps this is what you are thinking of. A radio station has to meet rules about the amount of spurious signals they send out and these spurious signals might cause interference, but this is rarely the case. It is almost always overload interference that is causing the problem and the radio station is not responsible for that.
 
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wolf9545

New Member
When I am on the phone I can clearly hear the radio station, sometimes I can even understand the commercials / interviews they are doing. This doesn't happen every time and sometimes when I am on the phone and I don't hear the radio station it will come in after a few minutes. Basically it is a random thing when I can hear the radio on the phone.
 
How loud is it? Is it just a little bit of faint noise, or is it so loud that you can't hear the person on the other end? If it is really bad, you may be able to modify an AM radio and connect it to a noise canceling circuit on the input of the phone line but since I don't know a whole lot about phones I would ask someone else here for help.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Any RF filter won't do. You need one specifically for AM. See Fixing RF Problems Placement is going to be a problem as well and you could end up needing a filter per telephone.

One other way to eliminate interference is to use shielded cables where the shields are earthed at oneend.
 

mvs sarma

Well-Known Member
the mod has to be done inside the phone instrument itself. Most older version phones had this mod. the modern phones you may keep a 0.1uF cap across the each pair of mic and head phone wires right at the place where the coiled coil is plugged.(inside the instrument).this should sort the issue.
I was doing these mods in Indian telecom scenario to serve suffering customers and visiting officers camping close to Radio Transmitters.

NOTE: Certain Telecom administrations wont permit mods on their instruments by users. In such cases, you can lodge a complaint seeking replacement of suitable phone for the critical location.
 
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Gary B

New Member
I’ve had problems like this before. One customer had the tower just a few hundred feet out a window behind his desk. I had to shield the phone, handset and even the coil cord between the desk set and the handset.

You can replace the phone wire running the three floors with shielded cat 5 and make sure that the shield is grounded at the connection block end only. Note: this will only help if the rest of the phone cable is properly shielded and grounded. Next, make sure that the service entrance protector isn’t a carbon block type. Gas tube or solid-state (in this case, I would go for gas tube) is desired because the phone line must be balanced. If there is even a little difference in resistance between one side of the line and the other, it will pick up unwanted signals.

If that doesn’t fix the wired phone, shielding the case of the phone is the next trick. Most but not all plastic housing phones have the inside of the case sprayed with a conductive paint. Ground it through an unused pair in the mounting cord. The wireless phone is probably hopeless since it is probably picking the signal directly out of the air. You can try a notch filter but, I have no idea how you could possibly squeeze it into the case since those things are already pretty tightly packed.
 

mvs sarma

Well-Known Member
using shielded coiled cord cause pain to user
thus i suggest decoupling the rf induction on the coiled cord by 0.1uFon each Mic and headphone pins at the entry point of the phone, this works effectively.
 

Gary B

New Member
I have not found that to be particularly effective on overload issues but, I have no objection to trying it; however, that may not be the best place to put it. Since many new phones use an electric mike, I worry about modifying the frequency range and sensitivity by mounting a capacitor across it. Second, since it is in the audio range already, that is probably not the nonlinear impedance that is actually detecting the AM signal. The signal needs to be bypassed to ground while it is still RF.

A couple of 30mh coils with .1μfd caps to ground in the tip and ring on the station side should make a very good low pass filter that will block anything above 4khz while still maintaining the 600 ohm impedance. Of course, you could get fancy by splitting the coils and use two 15mh coils in each side with the caps to ground at the equivalent half tap points. Just make sure the DC resistance of the coils is low enough so the loop current does not drop below 25ma. By the way, that is the drop dead point, 30ma is the preferred minimum.
 

mvs sarma

Well-Known Member
i agree with your concept.
How to control the induction on the coiled cord? (especially the MIC wires as the induced RF signal gets rectified right by the 1st transistor handling the audio signal and Later stages amplify the audio.) we hear it as Side tone, and even the distant person gets this very recovered audio.
On the line side, we need to have one cap on each limb, of 0.1uF /400V connected to ground.
 
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mvs sarma

Well-Known Member
@Transistor495, Let us not point out whose mistake etc,.
It is a problem and let us search for all possible and cost effective solutions.

Perhaps 50db suppression is nothing compared to few hundred KW transmitters.On the other side the said filter is to cost around $35+shpg. However i could not see the details or even a possible sketch.
I understand ,by 4 wire, that the filter is for the line side(2wires IN and two OUT. It doesn't cope for the induction the moment we stretch the coiled cord for speaking !!!
@Gary B, many modern voice chips of phones have facility to bypass this induction on the coiled cord. Issue arises from those old instruments, later converted to electret mic by a replacement capsule.. we In India still have some phones with same module as used for earpiece, working like dynamic MIC.
 
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Boncuk

New Member
I must strongly disagree. Both the law and accepted convention takes the viewpoint that radio broadcasting is very valuable and so it gets protection and preference by law. It is the electronic gadget that is suffering the overload interference that must cope with the radio station, not the other way around.

It is safe to say that makers of consumer electronics equipment tend to design their devices for only so much protection from interference, enough to deal with the majority of circumstances. The OP is, unfortunately, not within that majority and now has to deal with this problem himself.

I mentioned the term "overload interference" because this is the most likely kind that the OP is suffering. The other kind might be spurious signals and perhaps this is what you are thinking of. A radio station has to meet rules about the amount of spurious signals they send out and these spurious signals might cause interference, but this is rarely the case. It is almost always overload interference that is causing the problem and the radio station is not responsible for that.

Do that in Germany and your broadcast transmitter will be closed down faster than you can think. :)
 

wolf9545

New Member
I like the item here:

Fixing RF Problems

just because I can get one for the AM station that comes over the phone. The station sometimes is just quiet where I can hear a little static and some people talking to times where the radio is all I can hear. It doesn't matter what room I am in or what time of day. It does not happen every time though. Sometimes I pickup the phone and it is fine the whole time. My phone is 3 cordless phones but they all go back to the same base unit. I live in an apartment so I can not run new wiring from the base unit to the punch down cabinet in the basement.

I like the unit in the link I posted but I was thinking of just making one because this way if it doesn't work I didn't spend a lot of money on something that doesn't help. Any ideas on the circuit inside the device?

The cordless phones, I don't want to take apart and put something inside of them; still fairly new and under warranty. That is why I was looking for a circuit to build. Any other questions please feel free to ask.

Edit:
Oh, forgot to add that on any radio if you put it to the AM station that is the only station that comes through. No matter where you tune the radio that is all you hear. On FM you can hear the normal stations.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
Do that in Germany and your broadcast transmitter will be closed down faster than you can think. :)

You're talking rubbish I'm afraid, unless the station is broadcasting in breach of it's licence conditions? - I'm sure Germany has plenty of high power radio transmitters?.

The problem here is with the phone system, which appears to be poorly designed as regards external RF fields. The original CE labelling was specifically intended to prevent such problems, and presumably this doesn't meet those requirements - although as it was self certifying, most items were never actually tested.
 

JimB

Super Moderator
Most Helpful Member
Do that in Germany and your broadcast transmitter will be closed down faster than you can think. :)
Totally wrong!
Germany has had strict EMC regulations for many years and was one of the drivers for the European EMC Directive, one of the better ideas to come out of the European Union.

The EMC legislation effectively defines limits for various aspects of EMC, one of which is susceptibility to RF fields.
If the RF field strength is less than the limit and the phone is susceptible, technically and legally the problem lies with the phone, end of story.

JimB
 
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