PTEL Questions and Answers
to general FAQ's
This section is provided to assist
in troubleshooting some of the more
common problems encountered with wireless telephone systems. Before
starting any troubleshooting procedures confirm the Subscriber and Exchange
units are operating on the same RF channel. Both MUST be set to the same
channel for proper operation.
While these questions are directly related to our PTEL system they do apply to other Telemobile systems as well.
- My computer will
not connect to the Internet, why?
- I can hear other
people talking in the background.
- My phone sometimes
rings but there is no one there when I answer.
- My phone sometimes
disconnects in the middle of a call.
- There is an echo
or tunnel type sound to my calls.
- The audio is either
too high or too low.
- I can make calls
but I cannot receive them.
- I can receive
calls but I cannot dial out.
- When I try to
make a call I hear a loud tone on the line.
- I cannot make
or receive calls.
- The system connects but audio is not heard in one or both directions.
1. “My computer will not connect to the Internet, why?”
Connecting to the Internet requires
the link to be free of noise and interference. Address these problems
first if they exist. The quieter the noise level on the link, the better
the data rate connection speed will be.
Check the hybrid balance setting on the terminal and subscriber units,
see alignment section for further details on running this test.
The audio level into the dial-up modem may be set incorrectly. Normally
this isn’t a problem as the modem is designed to work over a wide dynamic
range.
On the Subscriber unit, first record the RX AF DIP switch audio level, then make small changes to the RX AF level into the modem by first increasing, then reducing the level.
Repeat for the Subscriber TX AF DIP switch level.
If changes to the subscriber side don’t remedy the problem, then repeat on the exchange side.
Check on the PC that the communication program is selected to run at speeds lower than V.90 (56 Kbps) and has the ability to negotiate to a lower rate. In tests carried out in the factory, data rates achieved varied between more than 19.2 Kbps and 7.2 Kbps dependant on the receive signal level and the level of noise introduced to the system.
If necessary, reinstall the modem drivers following the instructions that came with the modem.
2. “I can hear other people talking in the background.”
The most common cause is interference
from a transmitter located either in very close proximity to one end of
the link, or interference from someone operating on the same frequency
as the system.
Talk to your frequency coordinator and where possible, eliminate the source
of interference. Change channel to another frequency that you know is
available. For example, if you were operating on channel 1, switch to
channel 10, in order to move the new operating frequency as far as possible
from the one you were previously using.
Have the phone lines tested at the subscriber unit and exchange unit as
interference may be from a local AM radio station that is picked up on
the phone line.
Common causes are:
The TIP or RING lines may be grounded causing an unbalanced line.
An RF trap may need to be installed close to the either the exchange unit, or at the entry point of the subscriber’s telephone line into the building. The RF trap MUST be properly grounded in order to work and will remove the RF signal from the phone line when installed correctly.
3. “My phone sometimes rings but there is no one there when I answer.”
This may be caused by interference
from another system. If the ring cadence is correct then the problem may
be one of the following.
Strong interference from another system. Talk to your frequency coordinator
and where possible, change channel to another frequency that you know
is available. For example, if you were operating on channel 1, switch
to channel 10, in order to move the new operating frequency as far as
possible from the one you were previously using.
If the subscriber unit is not transmitting when the handset is picked
up:
Check the TX VCO is locked when Off Hook and the transmitter Power Amplifier for desired output. Check the frequency information programmed into the unit is correct. Refer to the programming section and the RF service manual for further details.
Check the frequency and deviation level of the 3825 Hz signaling tone are correct. Refer to the Alignment section and Test routines for details.
Check the subscriber power supply system and ensure the input voltage is within specification when the subscriber is transmitting.
Check the subscriber and Exchange units are operating on the same RF channel.
If the subscriber unit is O.K. but the exchange receiver is not working, for example the PWR ON LED does not light ORANGE when the subscriber unit is transmitting, then on the exchange unit:
Check the RX VCO is locked when the system is on, and the frequency information programmed into the unit is correct. See the programming section and the RF service manual for further details.
Check DET1 LED lights when the subscriber unit is Off Hook. If not check RX audio alignment levels and 3825 Hz decoder performance. Refer to the alignment section.
If the ring cadence is not correct:
Check the squelch setting on the subscriber unit is set correctly. See alignment section and the RF service manual for further details.
Check for interference from another transmitter.
4. “My phone sometimes disconnects in the middle of a call.”
Check the subscriber power supply
system and ensure the input voltage is within specification when the subscriber
is transmitting. Pay particular attention on battery backed up systems
to ensure the batteries are charged to correct levels for periods of no
AC power. If the system is operating from solar power, check the controller,
batteries and the system design to ensure sufficient power is present
for the usage of the system.
Repeat for the exchange system.
Check phone line wiring from the subscriber and exchange units for loose
connections.
A sudden strong source of interference to the exchange unit could cause
this type of problem. Talk to your frequency coordinator and where possible
either eliminate the source of interference or change channel to another
frequency that you know is available. For example, if you were operating
on channel 1, switch to channel 10, in order to move the new operating
frequency as far as possible from the one you were previously using.
Monitor the phone line into the exchange unit to ensure the telephone
exchange itself is not dropping the phone call.
5. “There is an echo or tunnel type sound to my calls.”
The most common cause is incorrect
hybrid balance settings. Refer to the alignment section for information
on running the hybrid balance tests at the exchange and subscriber sides.
The audio level from the Subscriber unit is set too high. Reduce the RX
AF DIP switch audio level to line.
The audio level from the Exchange unit is set too high. Reduce the RX
AF DIP switch audio level to line.
The transmit level from the Subscriber unit is set to LOW. Increase the
TX AF DIP switch level by 2 or more dB and retest.
6. “The audio is either too high or too low.”
When faced with audio problems,
first record the audio levels on the DIP switch of the system before making
adjustments. This ensures you can always set the system back to its default
configuration.
Always start at the subscriber side first!
Reducing the RX AF DIP switch audio level from the subscriber unit if the audio heard is too high. Increasing it if too low. If the desired results cannot be achieved at the subscriber unit then adjustment of the exchange side is required.
If the audio heard by the called
party on the exchange side is too high, then reduce the exchange unit
RX AF DIP switch audio level settings. If too low, increase them.
If the subscriber audio levels are too low or high after adjustments of
the subscriber RX AF then make small adjustments to the exchange TX AF
DIP switch transmit level to compensate.
Correctly setting the hybrid balance also may improve the audio quality
of the system. Refer to the alignment section for test details.
7. “I can make calls but I cannot receive them.”
If you can make calls this indicates
that the radio side of the system must be working correctly at both ends
of the link.
During an incoming call, monitor the FXO unit and ensure that the SYS
ACT LED glows ORANGE and follows the ring cadence during the receipt of
the ring signal from the exchange. If not:
Check the level of the ring voltage sent from the exchange. It may be too low. The PTEL7 is designed to detect a ring voltage >40 Vrms at a frequency between 17 and 68 Hz.
The phone line may not be properly connected to the exchange unit. Unplug it from the system and connect it to a telephone set to ensure the ring signal is heard.
If the exchange units SYS ACT
LED glows orange ensure that the transmitter is enabled and 3825 Hz tone
is sent in sympathy with the ring cadence.
On the subscriber unit check the SYS ACT LED lights orange in sympathy
with the ring cadence. If not:
Check the performance of the 3825 Hz decoder section.
Test the ring generator by following the procedure outlined in the alignment section under test routines.
If ring voltage is present at
the subscriber unit check the subscriber telephones ringer is enabled.
Most modern phones have a way to disable the ringer, ensure the switch
is ON to enable.
Ensure the telephone is designed to work with the ringing frequency the
subscriber unit is operating on. Most modern electronic phones will ring
over a wide range of frequencies. The subscriber units ring frequency
is 20 Hz unless ordered otherwise. In some countries that use high ring
frequencies with very selective ringers this may be the cause of the problem.
Contact the factory for further information on obtaining a custom ring
generator or suitable phone replacement.
Ensure that the loop length is within specification as excessive losses
on very long loops may be to blame. Refer to the specifications page for
details on maximum loop length.
8. “I can receive calls but I cannot dial out.”
In this condition the only cause
would be problems during dialing where the exchange will not recognize
the dialing information.
For DTMF dialing.
Increase the subscriber units TX AF level settings. E.g. was –3 dBm, change to 0 dBm and redial. This will reduce distortion of the transmit audio.
Recheck subscriber unit hybrid balance settings.
Increase the RX level of the exchange unit to ensure sufficient signal is sent to the telephone exchange.
Check exchange unit hybrid balance settings.
For Pulse/Rotary dialing.
Check operation of phone or replace phone with a working unit.
During pulse dialing the exchange line loop relay will be heard clicking.
Try switching phone set to 10 pps instead of 20 pps if possible.
Connect the subscribers phone to the exchange phone line and ensure it dials correctly. If not replace phone or contact phone company for further assistance. If O.K., contact the factory for further information.
9. “When I try to make a call I hear a loud tone on the line.”
This is caused by one of the units having the Hybrid Balance test enabled. The SYS ACT LED normally flashes orange during the test routine.
Check each unit to ensure position 1 of DSW3 is turned ON during normal operation to disable the test.
If in doubt re-test the hybrid balance settings on each unit. Refer to Section Two for further details.
10. “I cannot make or receive calls.”
For both sides of the link.
Check the antennas for proper operation and VSWR. Ensure they are pointed in the right direction and transmit power.
Check power supplies during transmission to ensure proper regulation.
The radio path is line of sight and not obstructed.
The units are kept away from strong sources of interference such as power generators or other transmitters operating on the same or close frequencies.
The subscriber unit the SYS ACT LED glows GREEN when Off Hook. If not:
Check subscriber wiring.
Check subscriber unit DC-DC converter.
Check phone line fuses and line over voltage protection circuitry. Refer to the line interface schematic and the FXS block diagram for further information.
NOTE: If you can run the Hybrid Balance test routine then this is probably not the cause of the problem.
11. “The system connects but audio is not heard in one or both directions.”
Replace or test subscriber telephone
instrument.
Check telephone wiring into the exchange unit.
Phone line fuses and line over voltage protection circuitry. Refer to
the line interface schematic and the FXO block diagram for further information.
NOTE: If you can run the Hybrid Balance test routine then this is probably
not the cause of the problem.
Check one or both units are not set to 4W E&M operation and connected
to a phone line. Refer to Section 3.6 for further details.
On both exchange and subscriber units. Complete check out of all RF boards.
Refer to the RF service manual # 1025 for further details.
Complete the alignment procedure for both subscriber and exchange system
boards. Refer to the alignment and test routine section for further details.
Page Last Updated February 3, 2004
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