NV Series PA Modification for Improved Performance in FM+HD and HD Modes

Transcription

1 NV Series PA Modification for Improved Performance in FM+HD and HD Modes IS10001 Issue March 2010 Nautel Limited Peggy's Cove Road, Hackett's Cove, NS, Canada B3Z 3J4 T nautel (628835) or F info@nautel.com U.S. customers please contact: Nautel Inc. 201 Target Industrial Circle, Bangor ME T nautel (628835) or F info@nautel.com support@nautel.com Copyright 2010 NAUTEL. All rights reserved.

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3 IS NV Series PA Modification for Improved Performance in FM+HD and HD modes INFORMATION SHEET 1 INTRODUCTION This document provides instructions to modify the subject equipment in the field. 1.1 Reason For Modification To improve performance in FM+HD and HD modes of operation for the NV series FM transmitters. The modification will allow the transmitter to comply with spectral limits at higher injection levels (elevated digital carriers). 1.2 Equipment Affected This procedure applies to NV series FM transmitters operating in FM+HD and HD modes which utilize NAPA20A Power Amplifiers in the RF power module and have two-hole core ferrites installed on inductor L1. Note: If the RF power module or individual PA has a DWA label, this modification has already been completed in the factory Minimum Software Required Software version 2.7 needs to be installed. Please contact Nautel if the transmitter is running with an older version of software. 1.3 Responsibility for Implementation of Procedure This procedure should be carried out by qualified station maintenance personnel who are familiar with the NV series FM transmitters. 1.4 Scheduling Implement this procedure at the convenience of station maintenance personnel. The transmitter can remain on-air (reduced power) while RF power modules are being modified individually; however, when the injection level is changed and settings are applied, there will be a brief interruption in on-air status (approximately 5 seconds). Additional interruptions may be necessary during the subsequent steps that optimize the transmitter s performance. Prior to commencing the procedure, ensure that the power module shipping hardware has been removed as per Unpacking and Positioning section of the Installation Manual. 1.5 Manpower Requirements The modifications described in paragraph 2 will require 15 minutes per RF power module to complete. Depending on your familiarity with the AUI, it may require an additional 30 minutes to properly create a new preset and optimize the transmitter s performance as described in paragraphs 3 and Special Tools/Test Equipment The following test equipment is required: Standard technician hand tools including a pair of long nose vice grips (Nautel suggests vice grip model LN6) Personal protective equipment - safety glasses/dust particle mask/gloves Vacuum cleaner NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 1 IS10001 Issue 0.3

4 1.7 Materials Required No additional parts are required. 1.8 Identification of Modified Assemblies Identifying modified assemblies will inform future maintainers of the current configuration. Use indelible ink to mark IS10001 on each PA PWB (NAPA20A) along with IS10001 next to the serial number sticker on the chassis for the RF power module (NAA56/01). You should also add this label to the chassis of the transmitter next to the serial number plate. 1.9 Publications Affected No publications are affected by this modification. 2 MODIFICATIONS (a) With the transmitter operating on-air, disable (switch down) ac power and remove RF power module #1 as described in the transmitter Troubleshooting Manual Removing and Reinstalling RF Power Modules. (b) With the power module on a bench, remove and retain the 14 sets of M4 hardware (screws and beveled star washers) securing the right hand side cover. (c) Locate inductor L1 on the PA PWB and confirm the two-holed ferrite is installed (see Figure 2). Position the power module on the bench in an upright position, fans down (see Figure 1). In this position, debris will fall away from the module. Utilize personal protective equipment as defined in paragraph 1.6. Figure 1: RF power module positioned upright with fans down Page 2 Issue 0.3 NV Series PA Modification for Improved Performance in FM+HD and HD mode IS10001

5 L1 Figure 2: Location of L1 on PA PWB CAUTION Take care not to damage the insulation of the remaining L1 wire loop. (d) Using a pair of needle nosed vice grips with the jaws set slightly smaller than the depth of the ferrite, carefully break the ferrite away for the wire loop (see Figure 3). It is advisable to slightly tilt the module to the side to ensure the ferrite falls away from the module. Clean away any ferrite debris from the module. If possible, operate a vacuum cleaner in close proximity to L1 while the ferrite is being broken away to minimize ferrite dust collection in the module. Figure 3: Vice grips used to break away ferrite core (e) Repeat step (d) for all nine PA PWBs (8 PAs A1-A8 and 1 IPA A9) within the RF power module. Vacuum away any debris from within the module. (f) With an indelible marker, mark each PA PWB and the RF power module chassis with IS Also mark the transmitter chassis on the rear upper left corner next to the serial number plate/label. (g) Replace the right hand side cover and secure using the hardware retained in step (b). NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 3 IS10001 Issue 0.3

6 (h) Reinstall the RF power module and enable as described in the transmitter Troubleshooting Manual Removing and Reinstalling RF Power Modules. (i) Repeat steps (a) through (h) with all remaining power modules including any spare power modules or spare PA s. 3 OPTIMIZE FM+HD / HD PERFORMANCE The following paragraphs describe how to configure your transmitter to operate within spectral limits and at optimal efficiency. It involves: recording the transmitter s current configuration settings and creating a new preset monitoring and optimizing the transmitter s ramp-up behavior optimizing spectrum and efficiency saving and recording the new configuration settings saving the new LUT (Look Up Table) Use the Process Flow Diagram and Worksheet in Figure 7 as a guide to perform this procedure. 3.1 Preliminary Tasks Verify the transmitter is operating without alarms in FM+HD mode, at the licensed Analog TPO with standard modulation (audio) present or HD mode. It is recommended that the Controller Average PA Dissipation and Controller PA Volts meters be loaded on the main screen to assist with this procedure (refer to the Operations and Maintenance Manual; see Figure 4). A passing spectrum plot displays 3 db or more margin (-77.4 dbc) between the IBOC intermodulation products and the blue mask (limit lines) on the analyzer (see Figure 4; red arrows represent margin). From the transmitter AUI, set the transmitter for Local control. Figure 4: Spectrum Analyzer with Average PA Dissipation and PA Volts meters Page 4 Issue 0.3 NV Series PA Modification for Improved Performance in FM+HD and HD mode IS10001

7 3.2 Optimize Transmitter Performance (a) Go to the AUI Menu / Hardware Configuration / HD Settings screen and record the Default LUT Height (forward gain) value on the worksheet (see Figure 7). Exciter A and B may have different Default LUT Height values. The value displayed on the AUI represents that value stored in the active exciter. Temporarily change over to exciter B, if applicable, and record the Default LUT Height on the worksheet. Change back to exciter A. From the AUI Menu / Presets screen, while viewing the active preset, record the current mode, power level (Analog or Digital), injection level and HD PA Volts on the worksheet. (b) Save a new preset by pressing the Save button in the Presets box on the left hand side of the AUI. The Save Preset window will appear and will display the current presets. Press the Please Enter a Name field and enter a new preset name via the popup keyboard; press the Save New button and then press Activate. The new preset will now be the active preset. (c) In the new (active) presets Other Audio Settings sub-menu, set LUT Index value to Flat. This is at the bottom of the drop-down menu. (d) At the top of the preset page, change the IBOC Injection value from the current setting (e.g., -20 db) to the new desired injection level. See Table 1 to determine the maximum allowable Analog TPO vs. injection level vs. frequency vs. transmitter type for FM+HD (hybrid) mode; or maximum allowable Digital (Total RMS) output power vs. transmitter type for HD (all-digital) mode. NOTE Note that for any FM+HD mode, the power level displayed in the AUI s Presets page is the desired analog power setting (TPO). The power reading at the top of the home page is also the analog portion of the FM+HD output. Table 1: Transmitter Maximum Power Levels vs. Injection Level vs. Frequency vs. Transmitter Type FM+HD Max FM+HD Max FM+HD Xmtr MHz MHz FM Max Max Type (Linear Int. b/w -20 & -10) (Linear Int. b/w -14 & -10) HD Max -20 dbc -14 dbc -10 dbc -14 dbc -10 dbc NV kw 32.0 kw 23.0 kw 17.0 kw 29.0 kw 21.0 kw 12.8 kw NV kw 24.0 kw 17.3 kw 12.8 kw 21.8 kw 15.8 kw 9.6 kw NV kw 16.0 kw 11.5 kw 8.5 kw 14.5 kw 10.5 kw 6.4 kw NV kw 12.0 kw 8.6 kw 6.4 kw 10.9 kw 7.88 kw 4.8 kw NV kw 8.0 kw 5.8 kw 4.3 kw 7.25 kw 5.25 kw 3.2 kw NV kw 6.0 kw 4.3 kw 3.2 kw 5.44 kw 3.94 kw 2.4 kw NV5 5.5 kw 4.0 kw 2.9 kw 2.1 kw 3.63 kw 2.63 kw 1.6 kw NV kw 3.0 kw 2.2 kw 1.6 kw 2.72 kw 1.97 kw 1.2 kw * Maximum Power is guaranteed into a 1.2:1 or better VSWR only. (e) Press Activate and monitor the transmitter behavior. NOTE The transmitter output power will be interrupted briefly as the system resets and the Spectrum Analyzer limit lines will change to account for the elevated digital carriers. NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 5 IS10001 Issue 0.3

8 (f) If the transmitter overshoots (i.e., exceeds the set-point) or the ramp-up time is too long (i.e., PA failures occur), press RF Off immediately and perform the Optimizing Transmitter Ramp-Up Behavior procedure in paragraph to correct or fine-tune the ramp-up characteristics, then return to step (g). (g) Perform the Optimizing Spectrum and Efficiency procedure in paragraph Continue to perform the Optimizing Transmitter Ramp-Up Behavior procedure in paragraph unless already done in step (f). NOTE Consider the effects of paragraphs and simultaneously, as either procedure affects the other slightly. (h) Steps (e) through (g) will be repeated for exciter B (if applicable) after all steps have been completed for exciter A, which includes step 4 LUT Re-Saving [see step 4(f)]. Figure 5: HD PA Volts setting in the FM+HD (or HD) Preset Optimizing Spectrum and Efficiency (a) Once the transmitter output power settles at the set-point power, monitor the 3 rd order inter-modulation products (spectral re-growth the humps that are just outside of the digital carriers) and the Average PA Dissipation meter reading and take the appropriate action based on the following two possible conditions: NOTE The HD PA Volts value should be decreased as much as possible to bring the intermodulation products within the 3 db margin. This optimizes efficiency by reducing the Average PA Dissipation reading. The HD PA Volts can be set under Menu / Preset; change the HD PA Volts value, then press Activate after each adjustment. It can take up to 30 seconds for the spectrum plot to re-stabilize. Page 6 Issue 0.3 NV Series PA Modification for Improved Performance in FM+HD and HD mode IS10001

9 NOTE For dual exciter systems, when optimizing HD PA Volts with exciter B (already performed with exciter A), if it is determined that the HD PA Volts can be further decreased to improve efficiency DO NOT (remember that exciter A needs this voltage setting to have 3 db of margin and both exciters share the preset setting). Instead, only increase HD PA Volts to improve exciter B s spectrum if B is worse than A with the same HD PA Volts (noting the 3 db margin and average PA dissipation limits). i. Does the spectrum FAIL but Average PA Dissipation is less than 130 W ( MHz) or 150 W ( MHz)? If so, in the Preset menu (see Figure 5) INCREASE the HD PA Volts value by 0.5 V (e.g., increase from 48.0 to 48.5). Repeat until the spectrum has 3 db margin (see Figure 4) and Average PA Dissipation is less than or equal to the limits specified. ii. Does the spectrum PASS but Average PA Dissipation is more than 130 W ( MHz) or 150W ( MHz)? If so, in the Preset menu (see Figure 5) DECREASE the HD PA Volts value by 0.5 V (e.g., decrease from 48.0 to 47.5). Repeat until the spectrum has 3 db margin (see Figure 4) and Average PA Dissipation is less than or equal to the limits specified. (b) If the requirements of step (a) cannot be satisfied, the injection level selected (or digital carrier power) is too high for the transmitter s configuration (i.e., licensed Analog TPO). Reduce the injection level in the preset menu (e.g., from -10 db to -11 db) and repeat step (a) until the requirements are satisfied Optimizing Transmitter Ramp-Up Behavior The following steps involve turning the transmitter on and off while monitoring its behavior. The optimal Default LUT Height (forward gain) value will be determined. Repeat these steps until the transmitter does not overshoot, and ramps up quickly and smoothly without alarms. (a) Press the Activate or RF On button and monitor the transmitter behavior. NOTE While overshooting of the transmitter power is quite easy to identify, determining optimal ramp-up time is subjective. i ii Does the transmitter output power overshoot? If so, press RF Off immediately and, in the Menu / Hardware Settings / HD Settings screen, decrease the Default LUT Height by 0.01, press the Set button and repeat RF Off/On while monitoring transmitter behavior. Does the transmitter power ramp up quickly (i.e., does it achieve % of power in less than 30 s) and smoothly without alarms (e.g., PA/Module Failures or Foldback)? If not, fine tune the ramp-up performance as follows: NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 7 IS10001 Issue 0.3

10 (1) When the transmitter finally settles at the setpoint power, monitor the AUI s AM- AM Correction instrument panel. Place the marker on the plot at the Table Index value shown in Table 2. Note that the values are based on the mode/injection level. Ensure the measured (LUT) Gain falls in the range specified. NOTE The Table Index Full Scale value in the lower right corner of the AM-AM Correction plot is actually 255, not The instrument panel can be increased in size by selecting the small, red up arrow. The left and right blue arrows adjust the position of the marker. The LUT Index value and Gain are displayed in the upper right corner of the instrument panel. Table 2: AM-AM Correction Table Index Values and Expected LUT Gain vs. Mode MODE TABLE INDEX (LUT) GAIN VALUE RANGE FM+HD Low Injection (-20 db to -16 db) 120 FM+HD High Injection (-15 db to -10 db) HD All-Digital to 0.44 (2) If the Gain value in step (1) above is greater than 0.44, increase the Default LUT Height value (and subsequently decrease the LUT Gain) to: Current Default LUT Height x (Measured Gain/0.44) Example: In step (1), if you measure a Gain value of 0.48 and your Default LUT Height value is 0.500, increase the Default LUT Height to (or x 0.48/0.44). (3) If the Gain value in step (1) above is less than 0.36, decrease the Default LUT Height value (and subsequently increase the LUT Gain) to: Current Default LUT Height x (Measured Gain/0.36) Example: In step (1), if you measure a Gain value of 0.32 and your Default LUT Height value is 0.500, decrease the Default LUT Height to (or x 0.32/0.36). (b) Record the new injection level, HD PA Volts and Default LUT Height (exciter A and B) on the worksheet. Page 8 Issue 0.3 NV Series PA Modification for Improved Performance in FM+HD and HD mode IS10001

11 4 LUT Re-Saving * LUT is an acronym for Look-Up Table. (a) With the transmitter operating at the preset power level with all objectives from paragraph 3 satisfied, go to the AUI Menu / Hardware Configuration / LUT Storage screen to review the stored Index details vs. the Index # in the table. For example, Figure 6 shows index 1 with a mode of FM+HD, a power level of 3.65 kw, a frequency of 98.1 MHz and exciter A active. In this example, index 1 is the only index to have a LUT stored. If others were stored in exciter A, they would appear under index 2, 3, etc. (maximum 12), and may have different modes (FM+HD or HD), power levels, frequencies and even injection levels (default is -20 db if not shown). The table shows the stored indexes for the active exciter. If applicable, exciter B indexes will have \B at the end in place of \A and there should exist an equivalent B index for every A index (same index # and description). (b) Select the LUT Name field and enter a name using the same convention as the existing LUT index (max 20 characters and \A or \B is not required considering each exciter stores its own LUT index details). Press the Save New button to create and store a new LUT. Note the index value. Figure 6: LUT Storage Sub-Menu (c) In the currently active Preset, change the Other Audio Settings -> LUT Index value to the index value noted in step (b) (e.g., 2 in this case, if only 1 was used). Press the Activate button. (d) Press RF Off then RF On. The transmitter should satisfy the requirements for ramp-up and spectral compliance. (e) If the transmitter is expected to operate exclusively at the licensed mode/power level/frequency (typical scenario), only one LUT (per exciter) is required. New LUTs for different transmitter configurations can be saved at any time, and selected for a given Preset by configuring the LUT Index for the associated stored index. (f) If exciter B is installed manually change over to exciter B (using the AUI Menu / Changeover screen) and repeat the procedure starting from step 3.2 (f) Optimize Transmitter Performance. Once complete, manually change over to exciter A. (g) Select the desired preset or operating mode. (h) The procedure is complete. NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 9 IS10001 Issue 0.3

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13 Figure 7: Process Flow Diagram and Worksheet NV Series PA Modification for Improved Performance in FM+HD and HD mode Page 10 IS10001 Issue 0.3