Kenwood TM-255E Bedienungsanleitung PDF herunterladen (Seite 29)

4 COMMUNICATION

PACKET OPERATION

One of the most exciting benefits of owning a VHF or

UHF transceiver nowadays is being able to use it for

data modes. Due to the ease of setting up a digital

station, even those inexperienced with this type of

operation can be on-the-air enjoying these new

modes quickly.

You can use almost any computer to control one of

the widely available Terminal Node Controllers (TNC)

since the computer primarily serves to input

commands and output received text data to its

display. Little real computing power is needed,

therefore a high-powered processor is not necessary,

and even a "dumb" terminal is satisfactory, at least to

start. As you become more experienced, you will

realize how well your interest in radio meshes with the

world of data communications.

Connecting to one of the many stations with gateways

to HF or satellite links can give you national and

worldwide messaging or conferencing capability with

other Amateurs with nothing more than your single

band VHF/UHF transceiver for the communications

link. Much reference material is available for getting

started in digital communications from any store that

handles Amateur Radio equipment. Or, if more

convenient, check the radio magazines for mail order

bookstores.

The most common mode used on VHF/UHF

frequencies for Packet operation is FM. However,

there is also some SSB PSK activity on the satellites.

Type Of

Keying

Modulation Mode /

Menu B, No. 77

Transmis

sion Rate

Emission

Type

OMSK.

G3RUH,

etc.

FM/ON

9600 bps

FID

FSK

FM/ON or OFF

1200 bps

F2D

PSK

SSB/OFF

1200 bps

G2D

Menu B,

No. 77

input Impedance

Standard Modulator Input

OFF

10 kQ

40 mVp-p

10 kQ

2 Vp-p

Consider the following before setting Menu B, No. 77:

• OFF: Transmit data input (PKD) sensitivity is

40 mVp-p. This is suitable for a typical

1200 bps TNC or other data

communications equipment.

• ON: Transmit data input (PKD) sensitivity is

2 Vp-p. This is suitable for most 9600 bps

TNCs. Set Menu B, No. 77 to ON if using a

TNC with dual speed capability that only has

a 2 Vp-p output. However, in this case, FM

mode must be used.

Using a modulator input level that is far different from

the optimum 40 mVp-p / 2 Vp-p specifications may

result in deterioration of S/N ratio or signal distortion.

This could result in increased errors or a complete

failure to connect with other stations.

If the modulator input level rises to approximately

4 Vp-p, the transceiver automatically switches to

Receive to prevent transmitting a distorted signal.

Transmission is not possible until the input level is

reduced by adjusting the TNC modulation level.

To receive after making the necessary connections as

explained in "PACKET EQUIPMENT" {page 5}, use

the following procedure and refer to your TNC manual

for further assistance.

1 Select the desired frequency.

2 Select the correct mode by pressing [AUTO/FM] or

[SSB/CW].

3 Select the correct Menu B, No. 77 (page 14}

selection based on the type of keying, transmission

speed, and TNC that you are using (see charts).

4 Turn the VOL control clockwise to set a

comfortable level if you plan to listen to the data

exchanges. Otherwise, leave the control fully

counterclockwise.

• The VOL control setting does not affect the

receive audio level from the DATA connector on

the Rear Panel.

5 Adjust the SQL control until the "BUSY" indicator

on the Display just disappears (threshold) while the

frequency is clear of any activity.

After beginning to receive stations, use the

Main Tuning control for minor frequency adjustments

to compensate for frequency drift while watching the

tuning indicator on your TNC. Do not use the RIT

control since it is important to keep your receive and

transmit frequencies equal.

To transmit, proceed to the subsequent steps.

6 Commands sent from your communications

terminal (either a computer keyboard or a "dumb"

terminal) to the TNC control your transceiver.

• Refer to your TNC instruction manual.

• Be courteous. Although packet protocol can

handle multiple stations on a single frequency,

overall throughput decreases due to packet

collisions during busy times of the day. Keep

transmissions short at these times.

7 Adjust the output level from the TNC while

watching the RF meter to avoid output power

saturation. Adjust for a maximum meter reading of

10 with a steady mark or space.

Note:

Inputting 9600 bps OMSK signals at too high a level or inputting

significantly distorted signals into the transceiver can cause

errors and a wide transmit bandwidth that may interfere with

other stations.

Always tune your transceiver to the exact frequency of the

station you are contacting. Failure to do so will result in

inaccurate demodulation of received packets and multiple

retries. Use the Main Tuning control (-5 kHz to +5 kHz) for

making fine adjustments as necessary.

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