3-4 PROGRAMMING AND DIAGNOSTICS MDS 05-2415A01, Rev. A
CAPABILITIES OF THE HHT
With the HHT properly connected to the transceiver’s DB-25 INTERFACE connector, the
following can be performed.
• Review operating parameters and diagnostic information
• Set the operating parameters of the radio
• Program user information
All of these tasks can be performed with the radio mounted in its final operating position
without the need for removing the top cover of the transceiver enclosure.
Review Operating Parameters and Diagnostic Information
The user can review the current settings of various operating parameters of the radio, as well
as monitor several key test points in the radio. These parameters include:
• Radio model number, serial number and date of manufacture
• Transmit and Receive Frequencies
• Supply voltage, Lock voltage and Regulator voltage
• Transmit Forward Power Output
• Antenna Voltage Standing Wave Ratio—VSWR
• Time-out Timer Length
• Squelch Tail Eliminator Status*
• RTS/CTS Delay Interval
• Soft Carrier Dekey**
• Push-To-Talk Delay
†
• Temperature Inside Radio Housing
The values of diagnostic parameters (voltages, signal strength, etc.) are updated once every
second to allow the technician to make adjustments while observing the HHT display. In this
way, you do not need to invoke the diagnostic command each time a control is moved.
* The Squelch Tail Eliminator circuit senses the end of the incoming data message (by
detecting the loss of the 1200 Hz mark/idle tone), and shutting off the receiver’s
audio before the received carrier drops. In this way, the receiver does not
misinterpret the squelch tail noise burst as data. The Squelch Tail Eliminator feature
is only available on analog radios.
** The Soft Carrier Dekey feature keeps the transmitter keyed for a short period
(typically 4 ms or less) after the RTU has sent the last data bit to the transceiver. This
allows the modem time to process and transmit all of the characters in each message,
and reduces the possibility of framing or BCH (cyclic frames) errors.
† Push-to-Talk delay inserts a programmed delay (typically 5 to 31 ms) between the
time the RTS or PTT line is asserted and when the transmitter is actuated. This is
done to prevent carrier overlap (two stations transmitting at once) and other timing
problems that could otherwise occur in some systems, especially those with
repeaters. Carrier overlap causes lost or corrupted data.
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