ing the need for re-tuning or use of the SHIFT control for re-centering.
One of four standard tone pairs can be chosen for operation from menu selection 6-5, as desired. The menu display shows the center frequency of the selected tone pair (see the table below for actual mark/space tone combinations). Set the Packet Tone Pair to match the tones generated by your TNC (these are usually set via terminal software or DIP switches - check in your TNC documentation).
Important Note! - if changing packet tone pair to other than 2025/2225 Hz, be sure to re-calibrate the tuning meter as outlined on page 85. The calibration routine is simple, and ensures your center tuning indi- cation matches the tone pair.
Packet Frequency Display Offset - You can dis- play the center frequency of the two transmitted carri- ers, (that is, the packet tone pair used), without any offset, instead of the actual carrier frequency. Recall menu selection 6-4and turn the main knob to select the offset (±3.000 kHz).
Note - The default display offset is -2.125 kHz (to match the default tone pair* in 6-5 above, and assum- ing LSB operation). Ideally, the display offset should match the default tone pair, which in turn should match those used by your TNC. If you would rather have the actual carrier frequency (without offset) displayed, set the display offset to 0.000 kHz.
Packet Operation
Select the NAR 2 (500-Hz or 250-Hz) filter for 300- baud packet, and press the [PKT] mode button on the front panel once or twice, so that the green LSB LED indicator lights along with the red PKT LED.
Transmitter adjustment is similar to SSB:
rPreset the RF PWR control counterclockwise, and set the METER selector to “ALC.”
rNow set your TNC to its “calibrate” mode, prefer- ably with both tones alternating, and adjust the MIC control so that the meter deflects to mid-scale. Your TNC’s “TX Audio” output may also be capable of adjustment via a potentiometer inside the TNC.
rSwitch the METER selector to “PO” and advance the RF PWR control for the desired power output.
PACKET TONE INFORMATION
TNC Tone Pair | Tone Center Frequency |
1070/1270 Hz | 1170 Hz |
| |
1600/1800 Hz | 1700 Hz |
| |
2025/2225 Hzø | 2125 Hzø |
2110/2310 Hz | 2210 Hz |
| |
øindicates default setting (used by normal convention)
When tuning, be aware that some common HF packet channels, such as “14.103” MHz, were origi- nally determined to correspond with an actual IF cen- ter frequency 1700 Hz lower (in accordance with an old TAPR convention). Therefore, if you have the Packet Frequency Display Offset (menu selection 6-4) set to match your TNC’s actual tones, the display shows 14.101.30 when tuned to the above frequency - which is the actual center of your receiver passband, and the frequency mid-way between the two FSK carriers you will transmit.
Initially, you may need to adjust the receiver IF shift slightly right or left to get the 500-Hz IF filters perfectly centered over incoming signals. Start with the SHIFT control centered, and try to establish a connection with a moderately strong signal on a clear channel. If the connection is poor (many repeats), move the SHIFT control slightly right, and see if the repeats decline. Continue in this manner until you find the best SHIFT setting (with minimal repeats), and use this same set- ting for all future HF packet operation.
1200-Baud FM Packet
The equipment setup for 1200-baud FM packet (above 29 MHz) is the same as for 300-baud packet, except that you may want to connect the squelch line of the TNC to pin 5 of the PACKET jack if you plan to use the squelch. Press the [PKT] mode switch until both it and the green LED on the FM mode button are lit. Tuning is much less critical in this mode, requiring no special adjustments. Also, the FM MIC GAIN con- trol in the top access panel has been preset at the fac- tory for proper deviation with typical signal levels, so you should not need to readjust it (you should adjust the Tx audio output level of your TNC, though, if your signal sounds distorted in the monitor).
To set up the transmitter for FM packet:
rStart with the RF PWR control counterclockwise.
rSwitch the METER selector to “PO” and set the RF PWR control for the desired power output.
