7.7 AMTOR Switching-Time Considerations
For operation in AMTOR Mode A (ARQ), your transceiver or transmitter-
receiver combination must be able to change between transmit and
receive within 20 milliseconds. Most semiconductor-based radios can
easily meet this specification. Many older tube-type radios that use
electromechanical relays operate very well in AMTOR Mode A (ARQ).
If the changeover from transmit to receive is too long, the minimum
working distance is extended; the signal to the distant station will
arrive before the station has switched back to receive. However, if
the transmitting station is further away, the transmission time over
the propagation path will delay the arrival of the signal until after
the station has switched to receive. For this reason, you may be able
to "Link with" stations across the country, but not across town.
If the receiving station's changeover from transmit to receive is too
slow, the transmitting station delay between "PTT" and "data send" can
be extended. See the ADELAY command in the Command Summary to adjust
the PK-232's AMTOR timing characteristics to compensate for this.
7.7.1 Suggested AMTOR Operating Settings
If you have trouble synchronizing with another AMTOR ARQ station, try
some of the following operating tips before calling AEA or deciding
that your radio equipment needs modifications:
o Try to work the distant station on Mode B (FEC) to establish that
the other station's system is fully functional.
o Don't use VOX control - use the PTT line from your interface.
o Turn off the AGC circuit - use the RF gain control to prevent
receiver blocking on stronger signals.
o Turn off all compression or other audio processing.
o Keep the AFSK audio input level to the microphone circuit as low
as possible - avoid overdriving the audio input stages.
o Disable the ALC circuit or reduce excessive ALC action; use more
effective RF antenna loading to adjust output power levels.
7.7.2 Possible Areas for AMTOR Performance Improvement
If switching-time problems persist, you may have to make changes in
the radio to eliminate excessive time delays:
o Remove large decoupling capacitors from the Push-To-Talk line to
allow faster PTT (transmitter) activation;
o Improve power supply decoupling, especially in audio stages.
o Do not use squelch.
In case you can't solve your radio's switching-time problems, please
call AEA Customer Service Department (see the front of this manual).
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