Connecting a PTC-II to a SEA-235 Transceiver:

The SEA-235 can be used for Pactor, but has a very limited continuous output power rating. It will be necessary to reduce the audio levels so that FSK and average PSK power is reduced to less than about 40 watts.

Audio connections: The audio cable from the modem can either be connected to the rear-panel terminal strip, or to the 9-pin data connector "P2". The P2 connections are as follows:

PTC-II Audio SEA-235 "P2" connector

(8-pin SCS DIN) (9-pin DB-9- see note)

---------------- -----------------

(Tx audio) Pin 1----(vio)-----Pin 7 (audio-in)

(Rx audio) Pin 4----(grn)-----Pin 6 (audio-out)

(PTT) Pin 3----(yel)-----Pin 4 (PTT in)

(Gnd) Pin 2----(wht)-----Pin 9 (ground)

(+12V) Pin 5----(blu)-----Pin 8 (12V out- see note)

Shell---(shield)---Shell

Note: To utilize the "P2" data connector for modem connections, the internal switches must all be in the "on" state.
Remote control: Remote frequency control can also be connected, either by wiring the PTC-II HF Audio connections to the terminal strip instead of P2, and using P2 for the SCS RS-232 cable (with the internal switches OFF). Alternately, build or buy a Y-cable to merge the RS-232 TxD, RxD, and ground signals from the SCS RS-232 cable to pins 2, 3, and 5 or the SEA-235 "P2" connector.

Airmail Options Settings:

Modem (TNC) connection:

Modem type: PTC-II
Comm port: COM1 or as appropriate
Baud rate: 57600
Show link messages: no check
Ignore CTS: no check

Reset modem: checked

Audio Tones:

Center Frequency: 1500
Check "USB"
TxD: 20 ms

Amplitudes: as appropriate, start with 100 & 100

Radio connection:

Check "Direct using PTC-II control port"
Radio type: SEA-235
Baud: 1200 (or to match radio setting, faster is better)
VFO: not used
Icom Addr (hex): not used
Set narrow filters: no check

Dial offset: 00

Caution -- Output power: The SEA-235 is not capable of continuous full-power output without an optional fan kit. The modem’s audio output levels must be carefully adjusted to keep the average power output level at 40 watts. The proper way to set the audio levels is with a RF wattmeter, but a DC ammeter that measures the radio’s power consumption can be used in a pinch. See "Audio levels" for more information.

AirMail Help ©1997-2008 Jim Corenman ke6rk