The MA3772 1KW HF Combiner

2 minute read
This post is part of the series 'The Racal 3700 Series':
  1. The RA3700 Series
  2. The RA3701 HF Receiver
  3. The RA3712 Dual HF Receiver
  4. The MA3752 Dual HF Drive Unit
  5. The RA3702 Dual HF Receiver
  6. The TA3762 250W Linear Amplifier
  7. The MA3772 1KW HF Combiner
  8. The MA3752 driving a TA3762 PA

September 2019

The MA3772 1KW HF combiner is intended for use in transmitter systems where the outputs from up to four TA3762 250W Linear Amplifiers are required to be combined to achieve higher final outputs. Two TA3762 amplifiers and one MA3772 will develop an output of 500W, whilst four TA3762s and two MA3772s will produce 1KW. In both cases the amplifiers are driven from a common drive unit in the MA3750 series via a passive SU501 Splitter Unit.

Monitoring of RF input levels and final output power (both forward and reverse) is provided in the MA3772. The results, together with heatsink temperature information are sent in parallel analogue form to one of the TA3762 amplifiers, which is designated "Reply". The "Reply" amplifier relays this information back to the drive unit via its ASCII link for metering on the front panel of the drive unit.
MA3722 Rear
MA3772 Inside

Interestingly, the basic internal chassis in the MA3772 is identical to that in the TA3762 amlifier. The board at the top is the Monitor board. The Combiner Module is in the centre with the output detector PCB on the right.

MA3722 Combiner-Module
MA3722 Block-Diagram

As the Block-Diagram shows, the Combiner Module actually embodies two identical Combiner Boards and one Output Detector board. Both Combiner Boards are used ONLY when two MA3772s are combined with four TA3762 amplifiers. It is easier to explain this with diagrams ...

500W Configuration
1KW Configuration

Regarding the SU501 4-way RF Splitter ...
The SU501 was specifically developed for these systems. However any 2-way or 4-way splitter may be used provided it satisfies the following criteria ...
The splitter must be capable of withstanding 0.5W of internal power dissipation should an unbalanced condition occur at the input. All outputs must be in-phase with each other.

Next post in the series:
The MA3752 driving a TA3762 PA
TA3762, SU501