NA 501 500W FM POWER AMPLIFIER 1 GENERAL DESCRIPTION The NA 501 isahighlyintegrated broadband solid-state Mos-Fe FM amplifier of 500W rated power, fitted inane unit 19" rack, which do not require any specific calibration to operate in the 87.5 + 108 MHz frequency range. Its compact size, high efficiency, wide mains range acceptance, low maintenance requirements and broadband construction, make this amplifier ideal in medium power repeaters, in unattended posts, in N+1 systems and as a reserve.
2 TECHNICAL FEATURES "(nna F— Hum i Jul The front control panel carries the power on switch, thé control meter, some alarm warning led’s and a RF monitor connector. On the bottom side, a ridding on the panel permits the output of the ventilation air. °e 0 At the RF monitor output, BNC type, a sample of the output power is available which is attenuated 54 dB typically (i.e. +6 dBm @ 500W output). Evenifthisoutput is fairly flats. frequency, autosuggestion touche this for accurate harmonica analysis.
2.2 THEREAFTER AND THE CONNECTIONS Thereat panel allocates the RF power and the VO ports in addition to the mains power cord and fuse, the earthling screw and an auxiliary mains socket on some models. The power cord is not removable. Fit is required a longer cable than that provided in the factory (roughly 2 meters long), a . suitable 3x 1.5 mm sq. power cord irreplaceable the original one.
2.3 TECHNICAL SPECIFICATIONS @ 1kW RF output if not otherwise specified Frequency range: 87.5 + 108 MHz RF input power 8W mom, 10 W max RF output power 500 RF input/output impedance: 500 RF input connector: N RF output connector: N RF monitor connector: BNC Harmonic and spurious emissions: <-70 dBc RF monitor attenuation: 54 dB, typ.
3 INSTALLATION AND USE 3.1 FOREWORD TO INSTALLATION Although easternmost special instruments are required, have skilled personnel install the Unit. To make best use of the Unit’s capabilities and prevent damage to the unit, comply with the recommendations throughout this manual.
3.3 WIRING INTO THE MAINS Then A 501 is powered bya single-phase line. Mains capacity must be at least 2k VA and the nominal voltage is 230Vac. In some countries, where 115Vac is the norm, this voltage must be internally stein the factory or by skilled people before installation.
3.5 CONNECTION Tomaximallyavoidearthloops, wire the modulation signal line directly on the exciter, with high quality shielded and preferably balanced cable. Ground the shield only on the exciter LF input 3.6 OTHER RECOMMENDATIONS The ambient temperature shall range between -candid +30°C (35°C max, peak). Advisable tobogganing -max thermometer on the wall to display any variation. Air conditioning at would obviously be the best solution, but installation and operating costs are generally excessive.
!! WARNING !! OPERATION WITHOUT THE ANTENNA OR WITH A FAULTY ANTENNA CONNECTION MAY CAUSE DEGRADATION AND POSSIBLE DESTRUCTION OF THE FINAL STAGE. THIS FAILURE SNOT COVERED BY THE WARRANTY. AVOID TO USE TOO POWERFUL EXCITERS. AN INPUT POWER HIGHER THAN 12W MAY PERMANENTLY DAMAGE THE RF TRANSISTOR CAUSING A COSTLY DAMAGE, TRICHINOSIS COVERED BY THE WARRANTY. ASTABLEANDPROPERLY REGULATED 20+25W EXCITER, LIKE NICOM'SNT200r NT ARE THE BEST CHOICE.
3.7 OPERATION Check that the antenna, the subsequent poweramplifierorasuitable dummy load disconnected the amplifier RF output. If the NA 501 drivesatunedtubeamplifier, check that the input of the power amplifier is already tuned on the wanted frequency. Control that the power cords are correctly connected tithe amplifier and its drive rand both the Unit are off. Before connecting tithe amplifier, control that the exciter power misstate zero ora very low level (<1 W) and the frequency is correctly set.
4 SERVICE AND MAINTENANCE Since the NA 501 is cooled by air, it is subject to clogging by dust. Because of the high-quality materials used in their manufacture, preinstalled asset for thunder “INSTALLATION AND USE,” twill not require special maintenance for quite some time. Aregularserviceroutine, mainly to remove internal dust is suggested overa6monthtoayearrate.
6 SERVICE MANUAL 6.1 SYSTEM DESCRIPTION 3 basic sections compose the NA 501: the RF amplifier box, the power supply and the control and metering section. The RF section comprises 1x 500W amplifier modules connected through strip-linecombiners. All the RF transistors are Mos-Petty. Low-pass filter with directional couplet completes the section, chichis completely screened bimetallic box, to comply with EMI requirements.
The NA 501 amplifier comprises 6 internal different modules/boards plus some spare components, as can be seen in the drawing of the inner contents and in the "General wiring diagram™; both comprised in this manual: ~The power supply transformer, rectifier and capacitor -The Switch Mode Power Supply regulator ~The RF control and measure board ~The input RF power splutter ~The 500W RF power amplifier module ~The output RF combiner, Low-Pass Filter and couplet For the detailed description of each module on the
6.3 Oversupply components The power supply components, other than the boards below described, are very few: mainly the power transformer with a power relay, a bridge rectifier and a power capacitor, which delivers the raw rectified de power to the AMPS regulator module. The unregulated de voltage, nominally 140 Vdc, may range 120+ 170 V. The primary tap on the power transformer is factory set on the 230V input, allowing a mains range approximately 200 + 250 Vac.
by the Unit controller, i.e. output current and voltage monitoring, status prompting and alert. A fast 80A semiconductor-grade protection fuse is screwed on the board: it may be fused by the crowbar protection in case of switching transistor damage. If this happens a first attempt to replace the fuse may be accomplished, after having verified the integrity of the power transistors. Usually something is broken so causing the fuse blow-up.
On this board a small negative rectifier and a regulator (TRS) provides the negative bias to completely disable the RF power, if needed. The positive regulator TR4 derives the positive 11.3V board supply from the +48V regulated line. 6.6 Therein power splutter The purpose of this simple board is mainly to divide the input RF drive power in two identical signals, one for each power amplifier module, providing a good insulation between each output port (>20 dB, typ. 23 dB minimum on the whole FM band).
6.8 Throughput power combiner, LPF and couplet This module is symmetric to the input power splutter and is another printed Wilkinson couplet, whose power management capability is obviously much higher than the input board. In this case the power balancing resistors are high power devices, whose center connection is referred to ground through an induct or, which discharges any static electricity on the antenna up to a relevant amount of power.
7 REPAIR AND REPLACEMENT OF DAMAGED MODULES The NA 501 is a high reliability Unit, as much effort was done in the design and development stage to assure the maximum reasonable working margin for each part, Nevertheless, as all Unit which works 24 hours a day for years, some failures are possible, especially in those environments ‘which over-stress the Unit, like hot or dusty or moist places, or subjected to wide mains fluctuations or static discharges and things like that.
same identical characteristics, fully tested at the factory. To replace the modules avoiding as much as possible to damage the new part or the old transistors, if not already broken, carefully follow the subsequent steps: 1) Remove the amplifier cabinet from the rack, after having disconnected from its rear connectors the RF input and output cables, the power supply and the control cables. Disconnect also the ground cable from its screw.
damage of the device. CAUTION: beryllium-oxide is toxic and must not be thrown with domestic refuse but in specialized toxic material disposals. No special handling precaution must be paid when the transistors or power resistors are not mechanically broken, apart those deriving from the handling of mechanically fragile (and very costly) devices. If the transistor or resistor flange is broken, avoid to get in touch with it and the brittle white exposed internal ceramic or inhaling dust of it.
20) Turn off the equipment, reassemble the screening covers and the bottom panel of the Unit and reposition it in its working location with full connections. 21) Perform a limited period of test at full power, i.e. 500 + 550 W and then reduce power at maximum nominal working level, i.e. no more than 500 W.