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Existing Application Notes
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Q. I don't have any of your fancy testing equipment
- how do I set up your modem to my radio?
A. Without access to proper communications test equipment
many parameters cannot be easily measured for fine tuning the integration
process.
The following method however, while not optimal, will often give acceptable
results.
Effective data transfer requires that the Nexion modem be properly matched
to the transceiver unit. Many manufacturers provide access to the audio,
busy and PTT signals by the way of an accessories connector and this is
where we must start. Contact the manufacturer of the radio and enquire
about available option boards and accessory connector cable assemblies.
When integrating a Nexion modem with a transceiver, if using both radio
and its manufacturers approved data interface, no modification to the radio
is normally required.
To integrate a Nexion modem to a radio, you will need:
A CRO
A computer with terminal program (Hyper Terminal, Tera Term etc.)
2 or more radios with modems for each.
Prepare
Set up 2 radios so you can talk with them.
Pick one as the sending unit to start with.
Setting input levels
Drive the sending radios microphone input to it's maximum (loud
noise / whistle etc.) and, using a CRO, measure the output voltage of the
option board / cable of the receiving unit. Because the sending unit was
driven to use its maximum deviation, the voltage measured at the receiving
radios data option output is the maximum reference voltage.
Apply a 1500Hz audio test tone from the modem connected to the
sending radio (AT&T3).
If the radio is fitted with a method of input adjustment*, modify
both it and the modems register S115 to achieve a voltage output of approximately
60%-70% of the previously measured maximum voltage. The 30%-40% spare is
to provide enough 'headroom' to avoid clipping the signal. Any distortion
or clipping will reduce data performance of the modem.
Using a CRO examine the signal and check for any distortion
to the signal. Fine tune by adjusting the sending modems S115 register
and the radios input attenuator*.
Setting output levels
Send a test tone from the sending modem (AT&T3).
At the receiving modem, using the output of AT%Q quality
reports, adjust S114 and the radios output attenuator* to achieve a level
reading of 900 - 1000.
Configure other units in the same way.
Setting Lead in duration S111
Once data transfer is reliable the lead in delay can be optimized.
Reduce the default setting, transfer some data and examine
the error count with AT%Q.
Continue reducing the S111 setting and testing until errors are
introduced.
Set S111 to a higher number.
* Manual attenuation is not a standard option on some
radios.
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