1200-Baud Fm Packet - Yaesu FT-1000MP Operating Manual

Operation
Mic Audio during Digital Operation
Microphone audio is muted whenever PKT or
RTTY is pressed. Transmit audio gain is still
adjusted, however, by the front-panel MIC
control. We recommend first setting the TNC
audio output to a sufficient level which allows
"fine" adjustment throughout the ALC meter
range with the MIC control.
ceiver passband, and the frequency mid-way be-
tween 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 estab-
lish 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 setting
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 control in the top access
panel has been preset at the factory 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:
Cj Start with the RF PWR control counterclockwise,
and set the METER selector to ALC.
Cj Set your TNC to its "calibrate" mode, preferably
with both tones alternating, and adjust the MIC
control so that the meter deflects to mid-scale.
1 Switch the METER selector to PO and set the RF
PWR control for the desired power output.
page 56
Note: Computer-Generated RFI
When using a TNC connected to your trans-
ceiver, or even having a PC located in the shack,
the possibility exists that you may experience
computer-generated RFI (Radio Frequency Inter-
ference).
The CPU in a personal computer operates with
a crystal-controlled oscillator (clock) and timing
circuits. Common clock frequencies include 8, 12,
16, 20 and 25 MHz. In addition, high-speed digi-
tal data switching uses square waves, which pro-
duce odd-order harmonic frequencies.
Computer-generated RFI may appear at
seemingly random frequencies (usually right
where a rare DX station is calling CQ!) throughout
the range of your transceiver, and may sound like
constant ticking or buzzing that may change as
you type or work within a program. Severe RFI
may have S-meter indications as much greater
than S-9, making copy of voice signals difficult
and data signals virtually impossible.
Computer-generated RFI is usually a result of
inadequate shielding of the PC's cabinet or I/O
and peripheral connections. While computer
equipment may comply with RF emission ap-
proval standards, this does not ensure that sensi-
tive amateur radio receivers will not experience
RFI from the device.
There are a few steps you can take to reduce
or eliminate computer-generated RFI. The first
step is to ensure that only shielded cables are
used for TNC-to-transceiver connections, care-
fully check RF ground connections and re-orient
your station equipment in relation to the computer.
Try moving your PC and peripherals slightly and
see if it has any affect on the RFI, in some cases,
this alone may be enough to correct the problem.
If not, several additional steps to try include
installing AC line filters on the power cord(s) of the
suspected equipment and inserting decoupling
ferrite toroidal chokes on interconnecting
patch/data cables and smaller ferrite beads on
single wires.
As a last resort, you can try installing additional
shielding within the PC case, using appropriate
conductive mesh/screening or conductive tape.
Especially check RF "holes" where plastic is used
for cabinet front panels. For further information,
consult amateur radio reference guides and pub-
lications relating to RFI suppression techniques.