MA79 Universal Drive Unit.



MA79 HF Transmitter.


This is one very nice piece of kit to own. Racal called it the "Universal Hf Drive Unit" but to us it is a Multi Mode Transmitter covering 1.6-30mhz LSB,USB,DSB,FSK and of course CW.

The design is similar to theRA117 and uses the same Wadley Loop idea to help cancel drift.

For tuning, the MA79 can be used with its own internal vfo,6 internally fitted crystal controlled channels,an external vfo in,say,an RA117 or an MA350B .Racal also made external crystal controlled oscillators for use with this and other Racal units.

When using this set with an RA117 full transcieve is possible by linking the vfo outputs to the vfo inputs on either set.In general,using the vfo on the RA117 is probably easier.A small control unit needs to be made for tx/rx switching and a mic amplifier will probably have to be made to match the balanced mic input.One other thing to note is that a linear amplifier will be required to boost the power output as,despite its size,the MA79 has an output of only 100mw.It is worth noting that the MA79 could be used to drive the TA184 HF Linear Amplifier.When you consider that this is rated at 10KW, then with this type of gain available 100mw was not a problem.Whilst this set is a transmitter the operation is very similar the the companion receivers.The mhz and khz tuning is the same and the RF stages have to be tuned in much the same way as the receiver.

Racal made a number of accessories for use with the MA79. The MA141 is a distortion indicator for use with the drive unit,the MA152 is an SWR meter, although it is rated at 300w -1kw pep, so the MA79 cannot drive it directly.Racal made Independent Side Band units for their receivers,and they did the same for their transmitters.The MA175 and the MA202 were such items and they modulated the MA79 by means of the 1.4 mhz IF socket on the rear of the set.


The MA284 enables the MA79 to be used with the MA350 Decade Frequency Generator.It replaces the oven containing the 1 mhz crystal.

The MA284 can be removed and the oven replaced for use as an MA79G.I believe that the reverse is not true as the MA79H has the sockets fitted for use with the MA284.

MA284 MA284

Two views of the MA284.

Things to look out for.

As,again,this set is similar to the RA17 then the same rules apply.I have seen some sets with only one sideband filter fitted (usb).End users sometimes specified their own requirements so things like this would not be uncommon.

Various MA79 Models.

MA79A Transmitter Drive Unit with internal 1 Mhz Standard. No provision for external modulation.
MA79A-Mod.1 With internal Standard and LA255 Tone to DC converter.
MA79B External frequency standard only
MA79C Not allocated
MA79D Without modulation
MA79E As MA79A modified for use with Admiralty "KG" box
MA79F As /A modified for use with Admiralty "KG" box
MA79G As MA79A with facilities for MA175 and MA202. Provision for external modulation ie ISB.
MA79G Drg DA15300/Z RAF
MA79G Drg DA15300/X G.C.H.Q
MA79H As MA79G but with MA284 fitted and new side members
MA79H Drg DA15300/J as MA79H but with metalwork as MA79G for use in Transmitter Cabinet DA14786/VAR
MA79H DA15300/Z1 RAF


Updated 05/03/2002

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