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7.7 AMTOR Switching-Time Considerations<br />
For operation in AMTOR Mode A (ARQ), your transceiver or transmitterreceiver<br />
combination must be able to change between transmit and<br />
receive within 20 milliseconds. Most semiconductor-based radios can<br />
easily meet this specification. Many older tube-type radios that use<br />
electromechanical relays operate very well in AMTOR Mode A (ARQ).<br />
If the changeover from transmit to receive is too long, the minimum<br />
working distance is extended; the signal to the distant station will<br />
arrive before the station has switched back to receive. However, if<br />
the transmitting station is further away, the transmission time over<br />
the propagation path will delay the arrival of the signal until after<br />
the station has switched to receive. For this reason, you may be able<br />
to "Link with" stations across the country, but not across town.<br />
If the receiving station's changeover from transmit to receive is too<br />
slow, the transmitting station delay between "PTT" and "data send" can<br />
be extended. See the ADELAY command in the Command Summary to adjust<br />
the <strong>PK</strong>-<strong>232</strong>'s AMTOR timing characteristics to compensate for this.<br />
7.7.1 Suggested AMTOR <strong>Operating</strong> Settings<br />
If you have trouble synchronizing with another AMTOR ARQ station, try<br />
some of the following operating tips before calling AEA or deciding<br />
that your radio equipment needs modifications:<br />
o<br />
o<br />
o<br />
o<br />
o<br />
o<br />
Try to work the distant station on Mode B (FEC) to establish that<br />
the other station's system is fully functional.<br />
Don't use VOX control - use the PTT line from your interface.<br />
Turn off the AGC circuit - use the RF gain control to prevent<br />
receiver blocking on stronger signals.<br />
Turn off all compression or other audio processing.<br />
Keep the AFSK audio input level to the microphone circuit as low<br />
as possible - avoid overdriving the audio input stages.<br />
Disable the ALC circuit or reduce excessive ALC action; use more<br />
effective RF antenna loading to adjust output power levels.<br />
7.7.2 Possible Areas for AMTOR Performance Improvement<br />
If switching-time problems persist, you may have to make changes in<br />
the radio to eliminate excessive time delays:<br />
o<br />
o<br />
o<br />
Remove large decoupling capacitors from the Push-To-Talk line to<br />
allow faster PTT (transmitter) activation;<br />
Improve power supply decoupling, especially in audio stages.<br />
Do not use squelch.<br />
In case you can't solve your radio's switching-time problems, please<br />
call AEA Customer Service Department (see the front of this manual).<br />
8/91 7-13<br />
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