Globalstar Product Management – Technical Support

GSP-2900 — How to Extend the Power/Phone Cable

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Is it possible to extend the 50-ft power cable which goes between the GSP-2900 and the grounding/junction box?

ANSWER: No.  The existing cable will need to be replaced.

    • Voltage: 10.7 to 16 VDC
    • Current:  3Amps
    • Power:  12W Typical, 36W maximum
  2. STANDARD POWER/PHONE CABLE: The power/phone cable which comes with the GSP-2900 is a custom cable containing both power and tip/ring phone conductors:
    • Part Number:  P/N CV90-81424-50
    • Length:  50ft
    • Conductors:
      1. One (1) pair of 14-gauge (AWG14) wire for power
      2. One (1) pair of 24 gauge (AWG24) wire for tip-ring phone service
    • Operation with Standard Power/Phone Cable:
      1. When connected to the factory-supplied power supply, the voltage at the end of the factory-supplied 50-ft 14AWG wire is 11.24VDC.
      2. There is no margin for extending the factory-supplied 14AWG cable.
      3. The power portion of the factory-supplied power/phone cable cannot be extended because the resultant voltage would be too low to power the 2900 in all of its modes.
  3. PROBLEMS Resulting from Adding to Factory Power/Phone Cable rather than installing New Cable:
    • If additional cable is simply added to the existing 50-ft power conductors, rather than replacing the entire length of the power cable:
      1. The power wire (factory wire PLUS your additional wire extension) will not be able to carry enough electrical current to run the phone
      2. You may experience one or more of the following problems.  Or you may encounter other problems that weren’t included in this writeup:
    1. Cannot Answer Incoming Calls
      1. No ringing:  The desk phone may never ring when someone calls.
        • Even though the caller may hear a synthetic ring tone cadence when they call, the desk phone at the remote location may not actually ring.  This is because the desk phone isn’t receiving enough voltage/current to operate the ringer.
        • The caller thinks the phone is physically ringing, but the phone at the remote location never actually rings, and therefore the person at the remote end doesn’t know someone is calling and never answers.
      2. Weak/Erratic ringing:
        • Depending on the desk phone, there may be enough voltage/current at the desk phone to make it ring, but the ringing may be weak or erratic
      3. Phone rings but call drops as soon as it is answered:
        1. The desk phone may ring well enough to alert the satellite phone user that there is an incoming call, but as soon as they pick up the desk phone handset to answer the incoming call, the line may go dead almost immediately, and then be followed by a dial tone.
        2. In this case, the subscriber is very puzzled because they can’t receive any incoming calls and they wonder if someone is playing games on them or if the phone company has partially deactivated their service.
        3. Neither explanation is correct.
      4. SOLUTION:  The solution is to replace the power cable as described in this article.
      5. Explanation:  However, if you are interested in understanding why the phone would act this way, here is the explanation.
        1. About 50 Volts DC is required to ring a desk phone.  The GSP-2900 has to create this voltage from the 12VDC that is supplied to it.  The factory cable PLUS additional wire, no matter how heavy duty the additional wire is, might not be able to carry enough electrical current through the extended cable.  In such instances, the more current the GSP-2900 uses, the lower the voltage at the GSP-2900
        2. When there is an incoming call, the desk phone’s ringer draws a lot of current in order to ring the ringer.  Since the power cable is not sufficiently sized, the ringing will result in a marginal voltage at the GSP-2900, maybe just enough to keep the GSP-2900 operating during the ringing operation, or maybe too low of a voltage.
        3. The resultant voltage drop may cause the GSP-2900 to power itself off during ringing.
        4. When the person picks up the phone, there is an additional momentary surge of power required.  This surge is just enough to bring the voltage at the GSP-2900 below it’s specified minimum and the GSP-2900 will power itself off moments after the person answers the incoming call..
        5. When the GSP-2900 powers off, the ringing stops, and there is no power to the deskphone handset even if it is off-hook, so the voltage of the GSP-2900 will return to an operational value and the GSP-2900 will power on automatically.  As soon as it powers on, the person at the “dead phone” will hear a dial tone.  In summary, they hear ringing, they anser the phone, they hear a momentary connection, followed by dead silence, followed by a standard dial tone.
        6. The calling party will hear an initial “ring tone” which will soon transition to a fast busy caused by the phone power-cycling itself.
    2. Cannot make Outgoing Calls:
      1. The power cable may not be able to carry enough voltage/current to operate the desk phone while establishing a call through the satellite system all the way to the Globalstar gateway far away.
      2. If someone tries to make a call from a GSP-2900, they might pick up the phone and hear a dial tone, and then shortly after dialing the call, or even during the call, they may suddenly hear dead silence, possibly followed by a dial tone.  Sometimes they just hear the silence and they have to hang up the phone and pick it up again to get a standard dial tone again.  then they try to dial again and the same problem might or might not occur, depending on how much power the GSP-2900 requires to maintain the radio link.
      3. Solution:  is to make sure that the power cable is properly sized.
      4. Explanation:  If you’re interested, the explanation for the problem is that during setup of a call, or even during a call, the GSP-2900 may have to use additional transmit power to communicate with the satellites.  If the GSP-2900 can’t get enough power through its power supply cable, the voltage drops enough that the phone will power itself off automatically to prevent damage to its circuits.  Once it turns itself off, the voltage at the GSP-2900 returns to within the specifications and the GSP-2900 turns itself on again.


If the 50ft factory-supplied cable is not long enough for your installation:

  1. Disconnect the existing 50-ft cable and do not use it
  2. Use a pair of larger gauge power wire for the entire length required.
  3. Use a separate telephone cable wire to connect the GSP-2900 Tip/Ring connectors to the Tip/Ring connectors in the lightning protection interface box


  1. .Since the voltage used by the GSP-2900, 12VDC, is so low to begin with, it is necessary to use very heavy wire as you extend the DC supply to long distances.  For example,
    • 100ft ==> 12AWG
    • 200ft ==>   8AWG
    • 300ft ==>   6AWG
    • 400ft ==>   5AWG
    • 450ft ==>   5AWG
  2. When using wire sizes larger than 12AWG to connect between the lightning protection interface box and the GSP-2900, you will need to add short pigtails at each end of the long extension cable to transition from the large wire to smaller wire in order to fit the DC wires into the connector blocks on the GSP-2900 and in the interface box
  3. Instead of extending the DC supply cable, we recommend that you evaluate the installation requirements to see if the lightning protection interface box can be placed within 50ft of the GSP-2900 while still providing full protection to the structure and the user.  If so, you can simply extend the AC supply as far as possible towards the GSP-2900, and place the GSP-2900 AC-DC power supply in a weatherproof enclosure.   This will result in a shorter required length for the DC cable, so that you can use factory-supplied 4-conductor cable to supply the 12VDC to the GSP-2900


  • TIP/RING: The GSP-2900 specification states that the tip-ring wire can be extended to a maximum distance of 182 meters (597 ft); our experience is that we can often go further distances. If you want to use longer cable, we strongly recommend that you test the candidate replacement cable before installing it, to ensure that it will work properly. Note that the likelihood of electrical interference increases as the length of the cable increases.


Additional keywords:  RAU, installation, GSP-2800, cables

Written by Joseph Crowley

September 15, 2017 at 8:13 pm

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