600W FM pallet amplifier – Planar

Description

Designed for FM radio transmitters, this amplifier uses the new inexpensive plastic easy to replace NXP LDMOS to produce > 600W (band centre at 50V)! In a design where easy serviceability was top priority the cost of this product remains very reasonable. Finals are very easy to replace. Please keep in mind that more expensive ceramic devices such as BLF184XR are more efficient and more robust than low cost plastic. Taking into account filter losses we recommend this pallet for 400-500W FM transmitters.

How is new planar version better than regular version?:
– Low profile (no coaxial cables in transformer)
– Improved reliability, coaxial cables can’t break off
– Better efficiency

Technical specifications:
– 28-50 Volts (maximum power at 50V, we have tested 52V and it does work but isn’t recommended)
– 87.5-108 MHz
– MRF300AN/BN 50volt LDMOS Technology
– Input/Output 50 ohms
– Input SWR: < 1:2.0 (planar)
– Pout ~600W max @ 3,5W drive / 50V / 100MHz
– Pout ~550W typ @ 3,5W drive / 50V / 108MHz
– >22 dB gain
– Low distortion class B push-pull
– >75% efficiency
– Size; LxWxH: 94 x 68 x 25mm (LxWxH)
– Aluminum base for better cooling
– Weight: 0,5Kg

IMPORTANT:
– Ensure shielding between final stage and audio stage with exciter. Install a good feed-through capacitor on the supply +48V wiring feeding the power output stage. This will keep and RF from the power line.
– Excessive drive level can damage this amplifier; design of equipment where the amplifier will be mounted must foresee an appropriate protection circuits.
– Amplifier efficiency is function of supply voltage, in order to obtain max efficiency please reduce supply in function of desired output power. Generally best compromise between efficiency and harmonic emission, is obtained when the amplifier work at about 2-3 dB of gain compression.
– RF pallets are sensitive devices, if you do not have sufficient experience please consider a fully finished product instead. They can be burned by applying too much drive power, too high supply voltage, not using proper heatsink, using filter with unsufficient specifications, connecting mismatched loads or no load at all and also by soldering coax with too long leads. For this reason there is no warranty for any pallet. We do assure you that every pallet is tested and is 100% operational as it leaves our workshop.

Warning: Do not exceed maximum supply voltage of 50V or damage will occur.

Note 1: Please use PTFE coaxial cable for RF input (RG178 is perfect) and output (RG178 or similar are perfect) connections, this makes it possible to have very short leads without burning the coax. Keep the coax leads as short as possible (few mm at most). Also keep leads short on connectors, this  N female flange for RG142 or .141 semirigid – easy install is perfect! Due to unusual hookup on this pallet thinner output coax is preferred so something like .141 semirigid or similar is best.

Note 2: A heatsink is definitely needed!

Note 3: Ensure each output transistor is fully in contact with heatsink. It must be completely flat and when purchased without heatsink you must install the pallet and re-heat the three pads on the transistors to make it fully ease down to the heatsink. After that re-tighten the transistor. Repeat, if necessary until transistor is completely flat on heatsink. Poor contact here will cause wild oscillations which will damage the output transistor.