On Fri, 11 Jun 2010 19:24:20 -0700 (PDT), Skip Gundlach
wrote:

My pactor is set for III but it bounces around depending on tx/rx
strength...

Assuming that your hardware is configured properly, Pactor 3 mode is
selected in the "frequency" pull-down of the Airmail Terminal window.
For example: 3580.0(P3)

If the frequency selection is not followed by (P3), you will not
connect in Pactor 3 mode.

Do you have the latest firmware loaded in your Pactor controller? I
upgraded mine last year and found that it improved my connection
speeds. You can download the latest version he

http://docksideradio.com/Firmware_update.htm

It is also important to have the Pactor audio output level set
correctly - too high and it causes distortion, too low and you are not
transmitting at full power.

Here is the process description from the Airmail help function:

Setting Audio Levels:

It is important that the audio output level from the Pactor mdem (TNC)
is set appropriately. Unless direct FSK keying is used, the modem
generates the audio signal that gets transmitted by the radio in SSB
mode. If the audio level is too low then the output power will be
reduced and communications will suffer. If the audio level is too high
then the transmitted signal will be full power but may be distorted,
perhaps severely, causing interference over a broad range of
frequencies. Besides being prohibited by regulation, such
"splattering" is also quite un-neighborly. The good news is that
setting the transmit audio level is relatively easy.

First, locate the adjustment. The PTC-II-family modems have
software-settable audio output levels which can be set from AirMail
using either the Options Window or the special audio-level toolbox
from the Terminal Window (Set Audio Level from the Control Window).
The KAM-98 and KAM-XL modems have software-settable audio levels,
adjusted via the modem's CAL command (use AIrmail's Tools/Dumb
Terminal window). The KAM+ controller uses an internal trimpot, R28,
and a jumper (J9) to select a high or low range. The PK-232 and MFJ
controllers use externally-accessible trimpots.

Also keep in mind that for many transceivers, the front-panel Mic gain
control is also active for the rear-panel audio input connection (even
though the Mic my be disabled), so be sure the Mic control is set to
the usual position before adjusting the controller.
To set the audio level you need to be transmitting. The objective is
to transmit full power, or close to it, without over-driving the
transmitter and requiring the ALC (Automatic Level Control) to crank
the power back, this is what causes distortion. Most ham transceivers
have built-in power-output meters as well as an indication of ALC
level.

First, find an unused frequency and start transmitting using Unproto
mode (Xmit Unproto from Terminal Window's Control menu). Starting from
a minimum audio level, increase the audio level and watch the
transceiver's output power meter - the power should smoothly increase
to the maximum level, or close to it, with no increase on the ALC
indicator. As you increase the audio level further, the output power
will no longer increase and the ALC will begin to increase instead.
Back off the adjustment until the ALC is near the bottom, well into
the "green" range, and the power-output about 60% of maximum. Click
the disconnect button to stop transmitting. Repeat this check on all
of the bands used as there may be differences. (If the differences are
large it may be an indication of RF feedback - see RF Isolation).

For a PTC-II controller there is a second audio level adjustment for
the Pactor-2 phase-shift (PSK) modulation. The PSK setting is
typically about 30% higher than the FSK level. Selecting PSK Unproto
will transmit a PSK signal and the PSK level can be adjusted as above.
Note that the average output power will be lower, this is because PSK
is a complex waveform and while the peak power is the same, the
average power density is about half of the peak.
Marine transceivers typically do not have an ALC meter, but the method
is the same. Increase the audio level until the output power level is
close to maximum and stops increasing, and then back off slightly. If
there is no output power indication, a DC ammeter provides an
excellent indication of output power. A transmitter putting out 100
watts will draw about 20 amps from 12-volt supply, and a marine
transceiver will draw up to 30 amps when putting out 150 watts. So
increase the audio level until the indicated current stops increasing,
and then back off to around 80 watts- 15-20 amps. .

Reducing the audio level, and operating with less output power, is
much better than too high a level and a distorted signal. The effect
of reduced output power is much less than one might expect. Your
signal will be reduced by one S-unit by dropping the power to half; in
other words to S-6 instead of S-7. A strong signal will still be a
strong signal, and a marginal signal will be only a little weaker.
Choosing the right time and frequency for good propagation, and
minimizing any on-board electrical interference will have a much
better payoff than trying to squeeze the last watt out of the
transmitter.

AirMail Help ©1997-2006 Jim Corenman