TNC2.18

Oftimes I hear packet operators complain about poor
performance of their stations when operating on fairly weak
links.  They have good antennas and good radios, yet they have trouble
connecting for no obvious reason.

When I asked them if they calibrated their TNC, they usually
reply "hunh???" and almost often say they haven't.

This is (usually) a simple procedure which can improve the
clarity and/or level that your data audio is transmitted from
your station.  You don't have to have a service monitor or other
fancy equipment.  5 minutes spent doing a simple calibration can
usually save hours in retries, disconnects and frustration.

WHAT YOU WILL NEED:

1.  Tools to open your TNC
2.  A radio to "listen" to your packet station
3.  TNC Owner's manual
4.  A tiny screwdriver to adjust the TNC's audio variable
    resistor

PROCEDURE:

1.  Open your TNC and locate the variable resistor.  (Your
    owner's manual may help you.)  On PK-88s, it's "VR-1", near
    the clock crystal on the left side of the board.

2.  Tune your station and monitoring radio to a simplex channel,
    set station radio to low power.

3.  Start the Calibration routine.  (Command is CAL on many
    TNCs, or check your owner's manual.)

4.  Transmit your calibration tone (by typing K on most TNCs).

5.  Adjust the volume on your receive radio so that it is clear,
    but not too loud.

6.  Adjust the variable resistor until the heard volume goes
    down, then turn it back up until it is "flattened out" by
    the limiter in your transmitting radio.  The idea here is to
    set the audio level right at limiting level in order to get
    full volume, but avoid distortion.  (If the TNC level is set
    too high, the apparent volume will sound the same through
    your receiving radio because the limiter cuts off the
    excess, but you will likely be transmitting some distortion,
    which can affect the "readability" of your transmissions.)

7.  Quit the calibration routine (usually by typing Q) and
    reassemble your station.  You should now be transmitting
    full, undistorted digital audio!

As with any such project... be sure to check your owner's manual
and make sure of what you're doing BEFORE adjusting your TNC.
Otherwise, if you're not sure, ask for help!

Good luck & 73, de Willis, N6VZT @ N6RFZ.#NOCAL.CA