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filter design to block phone and permit ADSL

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el00

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I find plenty of circuits on the web to block ADSL on the phone line, but I need the opposite: I am renting an apartment, and I want to allow them to use ADSL but not telephone: in fact the agreement is I pay for internet connection, but not telephone. My phone company does not provide ADSL without phone.
Therefore, I need to install a hidden filter inside the wall so that they cannot use the telephone. Of course I will remove all telephone equipments, but I want a permanent solution.
Of course I need passive filter, I cannot power it inside the wall.
I guess I need series capacitors, but if I close them on a resistor I need a large value, or I will load the line too much.
Thanks
 

You don't need a specific filter, a series capacitor prevents an analog phone from going off-hook.
 

You don't need a specific filter, a series capacitor prevents an analog phone from going off-hook.

Ok, but the input impedance of the ADSL modem is not infinite, so the risk is that the cut off frequency is shifted too high... what value for the capacitor, though?
 

The ADSL filters are Low-pass filters-you want a highpass filter. But your problem is more complicated because you don't want to distort the DSL signal. The 'normal' filters will distort the voice-band signals, but it doesn't matter too much, but if you start messing up your digital signals, you could have problems.

The normal voice-band upper end is considered to be 3.4Khz. But I'm not sure that would be a good enough cutoff frequency. Unless you can find a ready-made solution, this might require some experimentation.

Why don't you just NOT give your tenants DSL, lower their monthly rent accordingly, and make them buy their own? That's not a technical solution, but it's a solution.
 

barry,
I know that. In fact I am asking here, I know that it might be not easy.
Unfortunately I cannot do as you suggest because I rent for short term and ADSL installation / removal costs are very high, so I will keep the contract with my name.
 

Lowest DSL carrier is about 100 kHz, line impedance around 135 ohm. I would try a single 100 nF series capacitor.
 

Lowest DSL carrier is about 100 kHz, line impedance around 135 ohm. I would try a single 100 nF series capacitor.
I would think that would work.
As stated, all you need to do is block the DC current to the phone.
 

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