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Fax: (603)229-0434
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[Telephone connected to line 1][Connecting Telephones][Telephone connected
 to line 2]
[Telephone connected to line 1][Connecting
 Telephones][The Model 1040: Line 1 is Ringing Line 2]

Connecting Telephones Together

Northeast Innovations Hint #11 - Simulating the Attenuation of Long Telephone Lines

[1040E front][1040E front][1040E][1040E
back][1040E back]
[1040E front][1040E front][1040E][1040E back][1040E back]


It is sometimes desirable to add additional attenuation (line-to-line loss) to the Model 1040 Central Office Simulator when passing data between the two simulated telephone lines. Some of our customers have found that certain modem designs that would normally be connected to a telephone line with more loss than the Model 1040 provides connect more reliably with the additional attenuation in place. Another reason to add to the attenuation of the unit is to simulate the conditions of a weak phone line to see if the equipment you are testing will perform satisfactorily under those conditions.

If you would like to add line-to-line loss through the Model 1040A, 1040C or 1040E, a resistor needs to be placed between the Meter jack and the Ground jack on the front panel of the unit.

Materials Needed:

  • Northeast Innovations Model 1040A, 1040C, or 1040E Central Office Simulator
  • One 1/4 W, 5% tolerance resistor, the value of which depends on how much line-to-line loss you wish to add   (See the table below.)


Connect the resistor between the METER and GND jacks. Those are the two leftmost jacks when looking at the front of the unit. For a more permanent installation, solder the resistor directly to the jacks inside the unit (please see figure 1).


Warning: Only qualified personnel who are familiar with electrical safety procedures should remove the cover of a Model 1040. Before removing the cover, disconnect power and wait one minute to allow the power supply capacitors to discharge. Do not operate the unit with the cover removed. Solder an appropriate resistor to the specified location only.

Figure 1:   The resistor is directly soldered to the jacks inside the 1040 case. A 330 Ohm resistor is shown.

Line-to-line loss values we measured using nine different resistors:

All resistors are 1/4 W 5%.
* Note: All levels measured into 600 Ohms. These values were obtained using one particular unit and will vary somewhat among different units.
Resistance Value (Ohms) Line-to-Line Loss (dBm)*

For More Information:

If you have any questions about this procedure or that are otherwise related to the Model 1040 Central Office Simulator, we would very much like to answer them! You can find our contact information on our contact page.

[Back to the  Model 1040 Product Description Page]




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