The ATR4, ATR4A and ATR4B were among a number of small battery operated HF transceivers that were used by Australian Forces during WW2. Others included the Army Wireless Sets WS108 and WS208. ATR means Australian Transmitter/Receiver and is the terminology used by the RAAF. When used by the Army it became the WS 113.

The ATR4 was a single channel crystal controlled transceiver with a tuneable receiver covering the range of 5.5 to 7.5 Mc/s. It was developed from the RC16 set made by Radio Corporation in Melbourne, for country councils, regional fire authorities etc. and provided facilities for both voice and CW. It included a speaker in a deep hinged lid and behind the speaker was a clip for a hand microphone, Type No.3. The aerial wire also went behind the speaker panel which was hinged and held in place with a captive knurled screw. The set was fitted into a canvas haversack with a pocket for the earth spike, so that one person could carry it.

When adopted by the RAAF in late 1942, the RC16 was painted grey and had a new nameplate fitted inside the lid with RAAF Transmitter-Receiver, Type ATR4, the RAAF Ident. No. of Y10D/70363 and the Serial Number.

The chassis fitted into a metal box with a hinged lid that housed the speaker. It was held in by 5 screws through the sides of the case. The dimensions (closed) were 15 ˝” long by 8 5/8” wide by 6 1/8” deep (394mm L x 219mm W x 156mm D). It weighed 19 ˝ Pds. (8.86 Kg) in the haversack. The battery block was 15 5/8” long by 8 ˝” wide by 2 7/8” deep (397mm L x 216mm W x 73mm D) and weighed 3 ˝ Pds. (1.6 Kg) including the haversack and cables.

Power Supply.
The ATR4 required a dry battery pack that provided 3v LT for filaments, 180v tapped at 130v for HT and a –7.5v tapped at – 4.5v for bias. The battery pack was fitted into another canvas haversack along with the cables, antenna and insulators. On send the power consumption was approximately 0.78a at 2v and 46ma unmodulated on the 180v HT and 70ma modulated. On receive it consumed approx. 0.58a at 2v and 16ma on the 135v HT. In anticipation of heavy use a power cable was provided to allow the set to be connected to suitable heavy duty batteries of appropriate voltages.

Valve Lineup.
                        V1A                 1D5GT            RF amplifier
                        V2A                 1C7G               Converter
                        V1B                 1D5GT            1st IF amplifier
                        V3A                 1D8GT            1st Audio amplifier, Detector and BFO
                        V4A                 1L5GT             Audio power amplifier
                        V4B                 1L5G               1st Microphone amplifier
                        V5A                 1J6G                2nd Class B modulator
                        V6A                 1H4G               Crystal Oscillator
                        V5B                 1J6G                RF Power amplifier

ATR4.  Note that tuning scale only has graduations 0-10, there is an unused Speaker/Phone switch position on the centre right and  the jack at lower centre is labelled PHONE. On later sets there is no Speaker/Phone label and the jack is labelled as the MIKE jack. 

The front panel controls were engraved with their functions and from top left were:

AERIAL Terminal. The aerial was capacitance coupled and used a single wire or end fed half wave wire.

SEND-OFF-RECEIVE switch. On send the filaments and HT for the transmit section were switched on and the aerial changed over.

METER. The meter could be switched to measure filament voltage, HT voltage or the plate current of the RF Power amplifier.

EARTH Terminal. A steel spike with a short earth lead was provided with the set.

SPEAKER. A 3 pin socket for the speaker lead. Withdrawing the speaker plug allowed the set to slide out of the case.

MAIN TUNING. The dial was calibrated from 0 to 10 with an inner scale printed or engraved in red from 7 to 3 Mc/s. A 6:1 ratio vernier drive rotated the receiver tuning capacitor. The dial could be clamped in position with a screw clamp on the right.

METER SWITCH marked FIL.V. – B Bat. – M.A. The filament voltage of the transmitter was adjustable and needed to be set to 2v. on a scale on the meter. When the B battery voltage dropped below 140v as shown on the meter it was to be replaced. In the M.A. position the meter read the plate current of the Transmitter RF Power valve and was used for tuning it up.

(SPEAKER/PHONE). Curiously on some early sets there was provision for a toggle switch and indeed in a picture of the ATR4A in the RAAF manual the toggle switch is shown but never mentioned. On all ATR4 sets that I have seen the toggle switch hole has been filled with a washer and bolt.

BAT PLUG. A 6 pin Jones type plug for the battery cable.

B.F.O. ON. A single pole toggle switch.

MIKE. A standard socket for the hand microphone. Note that on the sets that had a Speaker/Phone provision this socket is labelled PHONE.

VOLUME. Self explanatory.

SET AT 2V. This is a wire wound rheostat for the transmitter filament voltage.

There were also controls recessed into the rear of the case:

KEY JACK. Although not labelled, a morse key could be inserted into a jack that protruded through a hole in the rear of the case.

TRANSMITTER AERIAL TUNING. Also not labelled but a small knob in a recess in the rear of the case attached to a variable capacitor allowed the transmit aerial circuit to be tuned.

ATR4A and ATR4B.
These two sets are basically identical and were the same as the Radio Corporation RC16B. Initially the ATR4A was made with a different BFO circuit but after serial no. 360 it was changed to that of the ATR4B. In addition the range of crystal frequencies for the ATR4B were slightly different to the ATR4A. The ATR4B was tropic proofed.

The ATR4A and ATR4B differed from the ATR4 by having two possible transmit frequencies, one in the 3 to 4.5 Mc/s range (ATR4B was 3 to 4.8 Mc/s) and the other in the 4.5 to 7 Mc/s range (ATR4B was 4.8 to 7 Mc/s).

ATR4B showing the speaker in lid at top.
 The RAAF ATR4A/4B were all painted grey. In the top right of the lid is a card for marking the operating frequencies. Just visible at the top rear of the case are the two covers over the HF and LF aerial tuning coil trimmers.

ATR4 (RC16) in an RC16B case.
RC16B's come in many colours! This case has been repainted a bright green and I have another that is bright blue. It is not uncommon to find various versions of the ATR4 (RC16) series in the incorrect case. The case with an RC16B nameplate seems most common.

ATR4A or ATR4B. Note the dial scale, again no Mc/s marked.

The nameplates were engraved with RAAF ATR4A Ident. No. Y10D/70584 or RAAF ATR4B Ident. No. Y10D/70429. The cases were painted grey with “TRANSRECEIVER ATR4A” (or ATR4B) and “RAAF” stencilled in black on the top of the lid. Perhaps around 800 ATR4A/B's were supplied to the RAAF. It appears that at least 1000 RC16B's were made.

The receiver remained basically the same as the ATR4 but the transmit circuitry was substantially more complex. It included switching for the two crystals (LF and HF) and the associated tuning coils. The chassis layout was altered somewhat to accommodate the extra components and different brackets fitted to mount them. Interestingly the circuit for the ATR4A/B shows a headphone connection to a spare pin on the 3 pin speaker socket. Therefore, a set of headphones with a matching 3 pin plug could be connected in lieu of the speaker but there is no mention of this in the manuals.

ATR4 bottom view.
 The receiver is at the top right and the transmitter circuitry to the top left. The 3 grey cans are the RF input, inter-stage and LO coils. The transmitter modulator components are on the bottom, to the right of the Trimax microphone Transformer.
ATR4A or ATR4B bottom view.
Showing the extra components on the bottom left for the second band. The keying relay can also be seen at the bottom, between the grey mike transformer and the rheostat.

The physical specifications remained as for the ATR4 and the front panel layout did not alter. However an extra switch was added into an enlarged recess in the rear of the set to accommodate a Frequency Selector Switch. In addition there were two holes in the side of the case covered by small metal discs that could be rotated aside to give access. Inside, two screwdriver adjust trimmers, one for LF and one for HF, allowed the transmit aerial circuit to be tuned to the centre of the tuning range.

ATR4 rear view.
 Top left is the aerial tuning cap, accessible through a hole in rear of case. Below it is the trimmer cap for the aerial tuning coil which can be seen in the centre, with a piece of blue tape around it. This version does not have a key jack.
ATR4A or ATR4B rear view.
 Top left are two trimmer caps for the two band coil at top centre. Below the coil is the frequency selector switch (left) and the aerial tuning cap (right), both accessible through holes in a recessed section at the rear of the case.

The modulated power consumption of the ATR4B was lower than the ATR4A, 56ma instead of 70ma., accomplished by increasing the grid return resistance in the RF Power amplifier circuit.

Initially the ATR4A and B included a keying relay in the secondary of the modulation transformer but this was modified to return to the method of keying in the grid return of the RF Power amplifier, as was used in the ATR4. It is not known when this mod. was introduced.

ATR4 top view.
The 5 valve receiver is along the bottom. The transmitter modulator and crystal oscillator are above. The RF Power amplifier valve is below the aerial tuning capacitor at the centre rear. In the bottom left corner is a 4 pin socket. I don't know its purpose as it isn't mentioned in the manual.
ATR4A or ATR4B top view.
 The 1J6G RF Power amplifier valve has been relocated to the top left. Next to it are 2 trimmer caps and below it is the dual band aerial coil. The 1D8GT receiver valve is missing, just below the dual coil and a 3V4 has been adapted to the 1L5 socket in the bottom left corner.

ATR4 side view. The crystal plugged into the valve socket. ATR4 Dial showing the red megacycles scale.

, Transmitter-Receiver Type ATR4 Ident. No. Y10D/70363 (7-8-’42)
RAAF Publication No. 692, January, 1946.
Instruction Manual Transmitter/Receiver
    Types ATR4A – Ident. No. Y10D/70584
    Types ATR4B – Ident. No. Y10D/70429
Instruction Manual for RAAF Transmitter – Receiver RC16B, RAAF Type ATR4B. Radio Corporation Pty. Ltd.

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