Racal MA942 Antenna Tuning Unit.

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The MA942 is an Antenna Tuning Unit that is suitable for use with the TRA931 and TRA931 / MA940B combination.

It is housed in a solid cast aluminium case and has been built to withstand a fair bit of abuse. On the front panel there are connections for a Dipole antenna via the BNC socket and a Whip or End Fed via a screw terminal. For use with a Dipole a "Shorting Link" needs to be in position and this is also on the front panel.


Frequency Range 1.6 - 30 Mhz
Power Rating 100w R.M.S Input
Input impedance 50 ohm
Antennas 12 ft whip 2-30 Mhz , 8 ft whip 2.5-30 Mhz Dipole 2-30 Mhz
Capabilities Whip: -iX not greater than 1600 ohm, R not less than 10 ohm. Dipole R not greater than 100 ohm
Limitations Unit will not tune an antenna that has (a) inductive Z >100 ohm (b) resistive component of Z exceeding 200 ohm
Operating Temp -10 to +55 dec C
Weight 6.35 kg
Dimensions 167 H x 357 W x 203 D mm

The unit will also tune an End Fed of an electrical length of a quarter wavelength or less.


The MA942 employs an "L Network" configuration with series capacity at the output. The input capacity is selected by means of fixed value capacitors. The tuning inductor is of a similar design to that fitted in the TRA931 and uses the same Gold Plated wire. There are only two controls "Tuning" which varies the inductor and "Loading" which switches the appropriate capacitor into circuit. The RF out put is sampled and rectified to drive a front panel meter with a FSD that corresponds to an antenna current of 3A

In Use

The MA942 is simple to use. Whips and non-resonant end-fed antennas are connected to the "Whip" Terminal. Dipoles are connected to the "Dipole" BNC socket and the dipole link is used. You set the load switch to mid position , and set the driver to transmit, you then monitor the output meter and rotate the "Tune" control for maximum reading on the meter. you then try adjacent positions on the "Load" switch to see if the antenna current increases. If it does you repeat the procedure until there is no further increase on the meter.

Below are some general views of the interior of the MA942

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The MA942/S is a marine version of the standard unit.


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