exciter data interface - rf technology · page 3 of 16 rf technology exciter data interface with...

Eclipse Series

RF Technology [email protected]

October 2005

Exciter Data Interface

Operation, Maintenance and Installation Manual

This Manual is produced by RF Technology Pty Ltd 10/8 Leighton Place, Hornsby NSW 2077 Australia

Copyright © 2003 RF Technology Pty Ltd

of 16 RF Technology Exciter Data Interface with OCXO option

CONTENTS CONTENTS

Contents 1 Operating Instructions 3

1.1 Data Inputs 4 1.2 Tx Input 4 1.3 Centre Frequency Transmission 4 1.4 Timing Considerations 4 1.5 Transmission Delay 5 1.6 Data Bit Rates 5 1.7 Data Errors 5 1.8 Support Software 5

2 I/O Connections 6 2.1 Polarity Selection 6 2.2 Delay and Test Frequency Selection 6 3 Circuit Description 6 4 Installation 8 5 Alignment Procedure 9 6 DMTX with OCXO and DMTX standard photos 10 7 Component layout drawing 11 8 DMTX Schematic with OCXO 12 9 DMTX Schematic (standard) 13 10 JP23 and R159 positions 14 11 Modifications to VHF TX board version 3 or earlier 15 12 Modifications to UHF TX board version 3 or earlier 16


OPERATING INSTRUCTIONS

WARNING

Changes and modifications not expressly approved by RF Technology could void your authority to operate this equipment. Specifications may vary from

those given in this document in accordance with requirements of local authorities. RF Technology equipment is subject to continual improvement

and RF Technology reserves the right to change performance and specifications without further notice.

1 Operating Instructions Identifying DMTX cards Part number 30/9114/003 or later have onboard facility to accommodate the OCXO high stability oscillator option. Part number 30/9114/001 is the standard DMTX card which relies on the main board TCXO for the reference signal. Identifying Transmitter main boards UHF transmitter main board 30/9103/0004 or later and VHF transmitter main board 30/9116/0004 or later have installed jumper link JP23 and audio signal routing for easy plug-in operation of the DMTX card. Note: Transmitter main board versions earlier than the above part numbers require modification as detailed in the rear sections of this manual for satisfactory operation with the DMTX card. DMTX Part no. 30/9114/003 or later with OCXO high stability oscillator The high stability oscillator (OCXO) option is available with the DMTX part no. 30/9114/003 or later. This option is for VHF transmitters only. In operation, the high stability oscillator replaces the 12.8MHz crystal in VHF transmitters as the reference oscillator. The OCXO has a stability specification of +/- 0.05 ppm at temperature range –30 deg C to 60 deg C. i.e. +/-7.5Hz accuracy at 150MHz. Digital and audio modulation inputs are provided without modification to VHF transmitters with main board version 30/9116/0004 or later with JP23. The digital modulation input is through the data interface and supplied DB9 connector. The audio modulation input is via the standard DB25 connector.


1.1 Data Inputs 1 OPERATING INSTRUCTIONS DMTX Part no. 30/9114/001 (standard card) This card utilizes the transmitter TCXO as the reference signal input. Digital and audio modulation inputs are provided without modification to VHF transmitter main board 30/9116/0004 or later with JP23 and UHF transmitter main board 30/9103/0004 or later with JP23. The digital modulation input is through the data interface module and supplied DB9 connector. The audio modulation input is via the standard DB25 connector. 1.1 Data Inputs Jumper JP1 can be set to accept either TTL or RS-422 input levels. The data polarity is selected by jumper JP3. The normal polarity is set so that a logic 1 input produces a negative frequency shift. 1.2 Tx Input The data Tx input is used to turn the transmitter ON. Both TTL and RS-422 level inputs are provided and are selected by JP2. The polarity of the Tx input is set by jumper JP4. The normal polarity is set so thet a logic 0 turns the transmitter ON. 1.3 Centre frequency Transmission The interface module can be configured by setting JP5 to transmit on the channel centre frequency during the delay period or when the test button is pressed. This is useful for transmitter tests and frequency calibration. In the normal configuration, the frequency output always follows the data input. 1.4 Timing Considerations The Tx input must be true at least 25mSec. before the start of the first data bit. This is to allow time for the transmitter to turn ON and for the receivers carrier detect circuit to operate. The Tx input may return to false coincident with the end of the last data bit, but it is more usual to keep the transmitter ON for a short period after the last data bit is sent. Some operators like to keep the transmitter ON between successive short data bursts to avoid the 25mSec. delay. This can easily be accomplished by programming the transmitter delay. The transmitter delay can be sent in one second increments between 0 and 15 seconds.


1.5 Transmission Delay 1 OPERATING INSTRUCTIONS 1.5 Transmission Delay The total transmission delay from the transmitter data input to the receiver data output is approximately (500 + 3.33* Km.) uSec. Where Km is the radio path distance in kilometres. System designers should keep in mind since at the higher data speed this is equivalent to several bits. 1.6 Data Bit Rates The direct FSK/NRZ transmission system employed can accept speeds up to 4800 Bps. It will provide low bit error rates on a clear channel at that speed. 1.7 Data Errors Radio channels are subject to various types of interference. In most cities interference free channels are rare if not impossible to finds. As with any data transmission system which is prone to interference, error detection and correction schemes should always be used where the integrity of the transmitted data is of concern. 1.8 Support Software The transmitter delay can be set using the TecHelp Software or Service Monitor. TecHelp and Service Monitor can be obtained through your dealer or distributor.


2 I/O CONNECTIONS 2.0 I/O Connections 9 Pin Connector (DB9)

Functions/Signal Pin Specification TTL Tx Input 1 0<0.8V, 1>2.2V

+Tx Input 2 RS-422 -Tx Input 3 RS-422 Ground 4 Ground 5 Ground 6

TTL Data Input 7 0<0.8V, 1>2.2V +Data Input 8 RS-422 -Data Input 9 RS-422

2.1 Polarity Selection Data Tx

Jumper Positions (-) JP3_ JP4_ Normal Polarity 1-2 3 1 2-3 Reverse Polarity 1 2-3 1-2 3

2.2 Delay and test Frequency Selection

Jumper Positions(-) JP4_ Frequency Follows Data 1 2-3

Frequency Shifts to Centre During Delay/Test 1-2 3 3.0 Circuit Description The following descriptions should be read as an aid to understanding the schematic diagram at the rear of this manual. Data and Tx Inputs: The TTL logic level inputs from the 9 pin connector are buffered by CMOS invertors U2b,c,d,e to obtain the complementary logic levels to control analog switches U3a-d. Jumpers JP1 and JP2 can be set to select the RS-422 inputs instead of TTL. Differential line receivers U1a and U1b convert the RS-422 inputs to TTL levels.


3 CIRCUIT DESCRIPTION Reference Voltage Source: D3 is a band-gap reference diode which supplies a very stable 2.5 volts. The U5a is used to double the voltage to 5 volts. VR1 is used to set the low frequency voltage reference. It can be adjusted between 2.5 and 5 volts. VR2 is used to set the high frequency voltage reference and can be set between 0 and 2.5 volts. Analog Data Signal: The buffered data input signal is connected to analog gates U3b and U3d. These are used to switch between the two pre-set reference voltages so that the input to voltage follower U5b follows the data input. Data Filter: Two four pole flat delay low pass filters are used to remove the high frequency components from the data waveform. The attenuation of the filter is sufficient to ensure that the transmitters modulation products do not encroach on the adjacent radio channels. The filter uses operational amplifiers U4a-d as voltage controlled voltage sources. The filter output is connected to the transmitters frequency control input to produce FSK modulation.


4 INSTALLATION 4.0 Installation 1. Remove the transmitters two side covers. Temporarily disconnect the cables

to the power amplifier. 2. Locate the “D” connector cut-out on the rear panel and remove any labels

which may be covering the holes. 3. From the top side of the exciter board install the 9 pin “D” connector using

two 4-40 screws. 4. Mount the four M3x12mm spacers on the PCB in the holes provided. The

spacers mount from the component side of the board with the screw thread end of the spacer through the hole. A shake-proof washer is used on the component side of the board and a flat washer and nut ate used on the bottom side.

5. For DMTX with OCXO option fitted: Remove the following components from the transmitter main board if the OCXO option is installed on DMTX card a. Remove R152 b. Remove Q29 c. Remove R143

6. For transmitters with JP23, main board version 0004 or later: Move JP23 links from Pins 1-2, 5-6 to 2-3, 4-5 Add R159, 270 ohm ¼ watt resistor for VHF transmitter or Add R159, 1 ohm ¼ watt resistor for UHF transmitter

7. For VHF transmitters with main board version 0003 or earlier Refer to the modification drawings at the rear of this manual Remove C112 and C117, connect the negative pads of C112 and C117 on the bottom of the board. Connect JP15 pin 5 to the positive terminal of C117 position (U7 pin 7) Bridge R140 with a 270 ohm ¼ watt resistor on the bottom of the board. Short across R139 on the bottom of the board. Using 7 x .2mm PVC insulated hook-up wire to connect JP15 pin 6 to the anode of D10.

8. For UHF transmitters with main board version 0003 or earlier Refer to the modification drawings at the rear of this manual Remove C117, connect JP15 pin 5 to the positive terminal of C117 position (U7 pin 7) Short across C112, R139 and R140 on the bottom of the board. Using 7 x .2mm PVC insulated hook-up wire to connect JP15 pin 6 to the anode of D10.

9. Plug the 10 pin socket connector on the end of the flat input cable into P1 on the interface module. Plug the interface module into JP15 on the exciter board and secure with four M3x6mm screws.

10. Re-connect the power amplifier cables and set the frequency shift according to the alignment procedure.

11. Set the jumper options as required and replace the covers.


5 ALIGNMENT PROCEDURE 5.0 Alignment Procedure Test Equipment Required Dummy Load - 50ohms, 50 watts Frequency Counter - 500MHz min., 0.1ppm accuracy Signal Generator - 1KHz square wave capable (TTL) Comms test Set - RF Demodulation OR Receiver (Discrim output) - RF Demodulation CRO - View signal waveform Jumper Configuration - Normal Polarity, TTL default VHF transmitter with DMTX Part no. 30/9114/003 or later (OCXO option) Step Input Measure Adjust for

25KHz Model

Adjust for 12.5KHz

Model

Adjust for 12.5KHz Model with OCXO

1 Press Front panel TX PB switch

Frequency Check centre frequency is

correct

Check centre frequency is

correct

Check centre frequency is correct

2 Tx Input = 0 Data Input = 1

Frequency VR1 to obtain the centre frequency -4.5KHz

VR1 to obtain the centre frequency

-2.5KHz


-2.0KHz


Frequency VR2 to obtain the centre frequency +4.5KHz


+2.5KHz


+2.0KHz

4 Tx Input = 0 Data Input = 600Hz TTL square wave

Use CRO to view demod.

waveform

MOD BAL for best square wave shape ie flat tops

and bottoms

MOD BAL for best square wave shape ie flat tops

and bottoms

MOD BAL for best square wave shape ie flat tops and bottoms

VHF or UHF transmitter with DMTX Part no. 30/9114/001 Step Input Measure Adjust 25KHz Model Adjust 12.5KHz Model

1 Press Front panel TX PB switch

Frequency Check centre frequency is correct

Check centre frequency is correct


Frequency VR1 to obtain the centre frequency -4.5KHz

VR1 to obtain the centre frequency -2.5KHz


Frequency VR2 to obtain the centre frequency +4.5KHz

VR2 to obtain the centre frequency +2.5KHz

4 Tx Input = 0 Data Input = 600Hz TTL square wave

Use CRO to view demod.

waveform

MOD BAL for best square wave shape

ie flat tops and bottoms

MOD BAL for best square wave shape

ie flat tops and bottoms


6.0 DMTX with OCXO and DMTX standard DMTX Part no. 30/9114/003 (OCXO option)

DMTX Part no. 30/9114/001 (standard card)

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exciter data interface - rf technology · page 3 of 16 rf technology exciter data interface with...

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