FM1-HD/FM2-HD RF Amplifier Installation and Biasing

Transcription

1 FM1-HD/FM2-HD RF Amplifier Installation and Biasing IS05010 Original Issue 07 October 2005 Nautel Limited Peggy's Cove Road, Hackett's Cove, NS, Canada B3Z 3J4 T F U.S. customers please contact: Nautel Maine, Inc. 201 Target Industrial Circle, Bangor ME T F Copyright 2005 NAUTEL. All rights reserved.

2

3 IS05010 FM1-HD/FM2 HD RF Amplifier Installation and Biasing INFORMATION SHEET 1 INTRODUCTION This document describes how to install and bias replacement amplifier pallets in FM1 or FM2 transmitters operating in Hybrid or Digital mode. 1.1 Equipment Affected This procedure is valid for FM1 transmitters that are used in FM1-HD or FM2-HD configurations and operating in hybrid or digital modes. Transmitters operating in analog mode require installation of Nautel Part # UM64 amplifier pallets and do not require biasing. 1.2 Responsibility for Implementation of Procedure This procedure should be performed by suitably qualified station maintenance personnel. 1.3 Scheduling This procedure should be performed as soon as possible to allow the transmitter to operate at rated power. 1.4 Manpower Requirements This procedure requires approximately one hour. The transmitter must be placed in an off-air status for the duration of the procedure. 1.5 Special Tools/Test Equipment The following tools and test equipment are required: basic technician hand tools such as screwdrivers soldering iron 2.5 mm hex-head screwdriver thermal (heatsink) compound two digital multimeters (DMMs) two 50 Ω, 0.5 W (minimum) dummy loads with adapters to connect to the RF Input (type N) and RF Output (type N) connectors on an FM1 1.6 Materials Required RF amplifier pallets, which contain the FET, are not considered field repairable. Each pallet can be replaced by a Nautel Part # kit (see Table 1). Table 1: Analog to Digital Upgrade Kit Qty Nautel Description Part # 1 IS05010 Documentation 1 UM64 Amplifier, RF, Pallet, FM1 2 CT38 Capacitor, Metal, Polyester, 10uF 100V 1 HT11 Lug, Solder, #6 FM1-HD/FM2 HD RF Amplifier Installation and Biasing Page 1 of 4 IS05010 Issue 1.0

4 2 INSTRUCTIONS 2.1 Transmitter Shutdown Mute the exciter. Turn off ac power to the exciter and transmitter(s). Disconnect cables from the RF output, RF input, and ac input connectors. Remove the FM1 s top cover. Retain the 26 sets of hardware. (a) Check and replace rear panel fuses FS1 FS4 as necessary. Defective amplifiers may also show signs of physical damage such as overheated components. 2.2 Amplifier Replacement Limited aids are available to assist in determining which of the four RF amplifiers have failed. As a basic guide, each amplifier has an associated 16 A fuse on the rear panel as follows: Figure 2: Fuse Locations in Rear Panel (b) Note orientation and location of the following wires in the defective RF amplifier pallet. Unsolder: the thick red wire (PA volts) the thick black wire (Ground) the thin brown coax shield and center conductor (RF Drive input) the thin control wire (various colors depending on amplifier location) the link (RF output) from the amplifier pallet to its associated RF Filter board RV1 (bias adjust) HT11 lug Solder Amp 1 Amp 2 Amp 3 Amp 4 Figure 1: Amplifier Location in FM1 (partial top view) Table 2: Fuse / RF Amplifier Relationship Fuse # Amplifier # Amplifier Location (referenced to top front view) FS1 1 Left most FS2 2 Second from left FS3 3 Third from left FS4 4 Fourth from left Figure 3: HD Amplifier Pallet (c) Remove the four cross-head screws and washers from the amplifier pallet. Remove the two 2.5 mm hex-head screws and washers near the FET. Do not remove the two nuts and washers (adjacent to the white ceramic FET body) that secure the FET to the pallet. Page 2 of 4 Issue 1.0 FM1-HD/FM2 HD RF Amplifier Installation and Biasing IS05010

5 (d) Remove the amplifier pallet. (e) On the new pallet, de-solder and remove the blue electrolytic capacitor. (a) Terminate the RF Input (SK04) and RF Output (SK06) connectors with 50 Ω dummy loads rated at 0.5 W each (minimum). (b) Disconnect the quick-disconnect from the top terminal of the fuse holder (FS1-FS4) corresponding to the replacement amplifier. Remove Figure 4: Blue Capacitor Location (f) Lightly coat the bottom of the replacement amplifier with thermal compound. Install the pallet in the FM1 noting the orientation. Install the four (4) cross-head screws. (g) Keep capacitor leads as short as possible. Solder the HT11 lug to one leg of one CT38 capacitor. Install this lug under the hex-head screw as shown in Figure 3. Install the remaining hex-head screw. Flat washers should be used between split washers and the objects being held. Solder the remaining capacitor leg to the PA volts pad (B+). (h) Solder the other CT38 capacitor to the B+ pad and ground pad (i) Solder the wires removed in step (b) to the replacement amplifier pallet. 3 TESTING 3.1 Amplifier Biasing You must bias the replacement amplifier prior to on air operation. The basic approach is to verify the power supply voltage and adjust the dc current to a prescribed level. Figure 5: Power Supply Fuses and Bus Terminals (c) Install a mutimeter, preset to measure 500 ma of dc current, between the wire disconnected in step (b) and the power supply (+) output terminal. The power supply (+) terminal is a copper bus bar located below the fuses, adjacent to the side of the FM1 chassis. Several red wires are attached to the bus. (d) Configure another multimeter to measure a nominal 50 V dc. Connect the multimeter between ground and the power supply (+) output terminal. CAUTION Ensure the meter leads connected to the positive (+) terminal do not accidentally short to ground or the negative (-) terminal of the power supply. (e) Turn potentiometer RV1 fully counter clockwise. Connect ac power to the rear of the FM1. CAUTION The RF amplifiers will have a nominal 50 V dc present at several locations. Take care not to touch or short out this voltage when making measurements or adjustments. FM1-HD/FM2 HD RF Amplifier Installation and Biasing Page 3 of 4 IS05010 Issue 1.0

6 (f) Verify the power supply voltage is between 46 and 51 V dc. (g) On the replacement amplifier, adjust RV1 (small square potentiometer) clockwise until the dc current matches the applicable level in Table 3. Table 3: Amplifier Bias Current vs Mode Mode FM (analog) FM+HD (hybrid) HD (all digital) Dc current 200 ma ± 4 ma 200 ma ± 4 ma 500 ma ± 10 ma (h) Turn off the ac power and disconnect the ac cable. Remove both multimeters and reconnect the wire to the fuse that was removed in step (b). (i) Disconnect the dummy loads. Install the top cover. Re-connect the RF and ac cables removed in paragraph 2.1. (j) The repair is complete. Return the transmitter to on air status. Page 4 of 4 Issue 1.0 FM1-HD/FM2 HD RF Amplifier Installation and Biasing IS05010