The Racal MA940B is a Transistorised Linear Amplifier running at 100W output and is suitable for use with a number of Racal equipments.
It can be used with the TRA906 "Racal Squadcal" ,TRA921 "Syncal" ,TRA922 "Comcal" , TRA931 "Syncal30" and TRA932 "Comcal30". It may also be used with drive units such as the MA79, see later.
Once again this is another unit built to withstand abuse. It is mounted into a cast aluminium case with the large aluminium heatsink acting as the chassis and , I suppose , unusually , the heatsink is to the front and is covered with a thin gauge plate. All the connections are on the front. There is a "on/off" DC powerswitch and two lamps are provided to show "DC" on and "RF out". Power in and power out are connected via BNC sockets and there are two multi-pin sockets to match those on the companion equipment. A two pin "Amphenol" connector is used for supplying DC input to the unit and a knurled thumbscrew is supplied for grounding.
TX/RX switching is achieved by grounding the relevant lines on the multi-pin connectors.When used with the TRA931 this can be via either the PTT line or the Keying line.
|Frequency Range||1.6 - 30 Mhz|
|Inputs||5W pep into 50 ohm. (see below)|
|Power Output.||SSB 100W pep, DSB, 25W,FSK 100W mean,CW 100W|
|Harmonics||Better than -40 db relative to full pep at the output of associated ATU|
|I.M Products||Odd order products better than -25db relative to each tone of a standard 2 tone test at full pep|
|Power Supply||28V dc @11 amps|
|Temperature range||-10 to +55 deg C|
|Dimensions||359 W x 167 H x 225 D mm|
The MA940B has a frequency range of 1.6 to 30 Mhz with a power output of 100W approximately. It has been designed to be used in the field, in a vehicle or in shipborne installations. Like the rest of the matching equipment the MA940B is fully waterproof and the power transistors have thermostatic protection against excessive temperature.
RF input is fed into an ALC control stage and is then fed into a pre driver stage with four transistors operating in Class A.Next there is a driver stage in Class B push pull configuration. Output is then fed into the Power amplifier which has four pairs of transistors operating as Class B push pull pairs.There are various stages of voltage and current protection to reduce the possibility of damage to the unit..
The unit is usually configured for a drive level of 5W pep. It is possible to alter this for a drive level of 1W and 100mw by changing internal links.It may be worth checking the status of these links before applying any RF to the unit if you are unsure of its original use. As well as the equipment mentioned above I understand that there is a shipborne installation that uses the RA1723 as the driver and an RA1792 as the receiver with the MA940B as the PA unit. So it is possible you may see these units configured for low drive levels. Obviously as the MA79 has an output level of 100mw or so this unit would be ideal for use with this set and is much more compact and RFI friendly than the TA99..!
There is no provision for filtering of the RF output built into the unit, instead reliance is made upon the ATU following the amplifier to reduce harmonics.
The manual gives very useful signal and voltage level lists to aid fault finding.
As you can see from the photographs below the boards are "sandwiched" above the heatsink.
The view above shows the "Low Level" board
This view shows the boards mounted on the heatsink,the lower one being the "Power" board
The TA940A model covers the frequency range of 2-12 Mhz.
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