INTRODUCTION
The MTR MK II is a portable transmitter and receiver for HF use in the Australian Army. It was made by PYE Australia in 1965. The transmitter and receiver are in a steel case, 15 x 14 x 11 inches, weighing 30 pounds, with a fiberglass lid containing the accessories. The transmitter and receiver are separate units, each 13.75 inches wide, and 6.25 inches high. The receiver is in the bottom of the case, and the transmitter in the top.
Picture 1: Front
The receiver is all solid state using 9 germanium transistors, and one diode.
It is continuously tunable, in 4 bands from 525 Kcs to 30 Mcs. It has a 455 Kcs IF frequency.
The bands are:
Band 1: 525 - 1630 Kcs
Band 2: 1.630 - 5.0 Mcs
Band 3: 5.0 - 15.0 Mcs
Band 4: 14.8 - 30.0 Mcs
The transmitter is a hybrid using 4 valves and 9 germanium transistors. The transmitter has 5 crystal controlled channels in the frequency range 2 to 10 Mcs, and it is capable of AM and CW. It produces 23 watts CW, and uses a long wire aerial. It is powered from 12 volts DC (positive earth), consumes 100 mA on receive and 6.5 Amps on transmit.
Picture 2: Cover
There was a previous version called the MTR1 Mark 1 made in 1961 and used by the Australian Navy. This was painted grey and the transmitter and the receiver were a single unit.
CONTROLS
The receiver has a large Eddystone dial, with the 4 bands calibrated in frequency, and a 0 to 500 logging scale at the bottom. There is a large knob, used to tune the frequency. It has a flywheel so it has a nice feel to it. To the right is the band change switch, with 4 positions. To the left is a separated RF GAIN and AF GAIN control. The RF Gain ncontrol can be pulled out, to turn on the BFO feature. The BFO is fixed in frequency. Despite this, it is easy to resolve SSB signals. To the far left are 2 jacks, one for headphones, and the other for an external speaker. The speaker is mounted on the left of the panel. There is no waterproofing. The receiver has no nameplate.
Picture 3: Receiver
The transmitter has very simple controls. There is a 3 pin Bulgin plug on the left had side, for 12 VDC power entry. Next to this, is the 5 position CHANNEL switch. In the middle is the main FUNCTION switch, which selects OFF, and then REC ONLY, which merely runs the receiver. The next position is labeled REC & TX VOICE, and this powers up the valve heaters. When a microphone is plugged into the MIC/KEY socket, the microphone push button has a PTT function, which applies HT and produces AM modulation. The right most switch position is labeled TX CW ONLY, which applies HT. When a morse key is plugged into the MIC/KEY socket, CW is produced. There is also a 10 Amp fuse for the 12 VDC input.
Picture 4: Transmitter
To the extreme right is a METER switch, which selects 7 meter functions. The scale is calibrated in 0-15 and 0-300. The LT meter switch position shows the 12 volts DC input. The next position is labeled REC and shows the receiver AGC level. The third position is labeled HT and shows the transmitter voltage. The top position is labeled DRIVE and shows the RF level applied to the PA amplifier. The next position is labeled IkPA and shows the final valves combined cathode current. The next position is labeled TUNE and shows the ANTENNA current. The last position labeled MOD shows the AF modulation level.
At the top left are 2 terminals for the ANTENNA and EARTH connections. At the left is the PA TUNE control, which tunes the PA tank coil. In the centre is the nameplate, and a logging chart. This allows you to write in the TX and RX channel frequencies and tuning details.
RECEIVER DESIGN
The receiver is joined to the transmitter with 2 cables. The power enters the transmitter, then passes through a 3 pin plug and cable to the receiver. The third pin is the AGC return, to be shown on the meter. There is also a coaxial connection to the receiver for the aerial connection.
The receiver consists of a large printed circuit board, which holds most of the components. At the right hand end (front view), is an RF chassis that has the 3 gang tuning capacitor, all the RF circuits and trimmers, and the band change switch. The chassis is tilted to allow easy access to the trimmers and coil slugs, for alignment purposes At the other end is the speaker. There has been a modification fitted, to place a protection diode in the 12 volt power line, to prevent damage from accidental reverse polarity.
Picture 5: Receiver Top
Picture 6: Receiver Underneath
The printed circuit board has the components underneath. It is a single layer SRBP board, that has been hand layed out. There is plenty of room for soldering the components.
The receiver is a conventional single conversion super-heterodyne, with one RF amplifier, two IF amplifiers, and separate transistors for the oscillator and BFO.
The audio amplifier has two transformers, an AC126 as the audio driver and two AC128 output transistors. There is a bias stabilizer for the audio output transistors. There is a simple audio feedback circuit. It provides plenty of volume.
There are two AF114 transistors in the IF amplifier, and three IF transformers, each having only a slug tuned primary. The audio is rectified by an OA90 diode, and in addition this provides the AGC. This is applied to the bases of the first IF and also the RF amplifier.
There is an RF gain control which adjusts the emitter voltage, also of the first IF and the RF amplifier. The RF gain control has a pull switch, which powers the BFO. This is on a separate small PCB with one AF114 transistor and a transformer, probably the same as the IF transformers. It is slug tuned.
The mixer is another AF114 transistor, which uses a separate AF114 oscillator transistor. There is a ZENER diode to provide a regulated voltage to the oscillator. The mixer has a single winding tuned circuit, which is capacitor coupled to the IF amplifier. There is a three gang tuning capacitor, one gang for the oscillator, one for the mixer input, and one for the aerial circuit. Each gang has four RF coils, with associated slugs and Philips beehive trimmer capacitors. The RF amplifier transistor is mounted on the band change switch.
Fig 1: Receiver Circuit
Fig 2: Receiver Circuit
TRANSMITTER DESIGN
The transmitter is a hybrid, consisting of a mixture of 4 valves and 9 transistors.
The transmitter oscillator is a valve type CV4063 (M8082), with five crystals, one for each channel. There is a buffer amplifier, also a CV4063, with tuned plate circuits, one for each channel. These are fixed, and aligned to the crystal frequency, when the crystals are installed. At this point the DRIVE voltage is sampled for the meter.
Fig 3: Transmitter Circuit
The power amplifier consist of two QQE03/10 (CU2798 or 6360) valves. These go to a tapped coil, and then to the aerial terminal. There is an aerial changeover relay for the receiver. There is a tap on the coil for each channel, and this is set during alignment. The coil is tuned by the PA TUNE loading capacitor, which will vary depending on the length of the aerial wire connected. There is a pickoff point, so that the aerial current can be shown on the meter.
Picture 7: Transmitter Top
Picture 8: Transmitter Underneath
The 280 volt HT voltage is provided by a two transistor inverter, and a bridge rectifier. The two OC35 transistors are mounted on the back panel.
The modulator is on a printed circuit board, and uses a 3 transistor amplifier, using an AC126 and two S5760 transistors. This then goes to three OC35 power transistors, mounted on the back panel. These are transformer coupled, and use a modulation transformer. There is an audio pick off winding, to display the MOD level on the meter. This voltage is also used for feedback to a compressor, to prevent over-modulation.
Picture 9: Rear Panel Transistors.
There is an AC128 transistor, connected as a diode, which prevents the transmit relay from operating, if the power supply is reversed. This provides reverse polarity protection, for the inverter and modulator.
Picture 10: Relay Diode
ACCESSORIES
The cover for the case, is a fiberglass lid, which has a pocket inside. This contains the required accessories. There is a small morse key, and a microphone, both made by PYE. There is a pair of SG Brown headphones.
Picture 11: Accessories
There are several cables in the cover as well. There is a long wire aerial, a small rope to allow it to be attached to trees or other convenient supports. There is an earth lead and an earth stake. There is also the power cable. There are Operating Instructions on a panel inside the lid.
Picture 12: Aerials
The aerial wire is actually 2 lengths, of which half can be used above 4.5 Mhz. They are joined together by a plug for operation below 4.5 Mhz.
RESTORATION
The radio looked new or near new, and required very little cosmetic attention, apart from a little dusting.
The receiver was removed, and it appeared to be original, with no visible modifications. Closer inspection revealed that several capacitors had been replaced. Power was applied, and slowly increased to 12 volts, while the current was monitored. It drew little current, and there was no speaker noise, until the AF control was turned and there was some crackling heard. There was no noise from the aerial, tuning or BFO adjustments.
Injection of AF from a signal generator, was attached to the volume control, and that showed that the audio stages were working properly, and there was plenty of gain.
Injection of 455 Khz from an RF generator, showed that the second IF amplifier was working but the first was not. The voltages were wrong on the AF114 transistor, so it was replaced. The IF was now working but the mixer was not functioning, and voltages there were not correct as well. The mixer transistor was changed, and now there was activity on all bands. The IF transformers were aligned, but they were correct, and did not need it. The sensitivity was checked, but the frequency calibration was way off, and for a while I thought I was tuning into the image frequency. Then I found the grub screws were loose on the tuning shaft, and after resetting, the calibration was good on all bands. The receiver completely stopped, and both the RF amplifier and oscillator had failed. New transistors restored operation.
It was difficult to test the sensitivity, as the RF gain control had a strange hysteresis to the level. The AGC electrolytic capacitors were renewed again, as they had been replaced before, and on close inspection, one was found to be wired in backwards. New capacitors made the AGC and RF gain control behave normally.
The sensitivity was checked for a 10 dB signal to noise ratio, and it was found to be exceptionally good.
BAND FREQUENCY Microvolts FREQUENCY Microvolts
1 550 Khz 40 1600 Khz 15
2 1.8 Mhz 1 5 Mhz 1
3 5 Mhz 1 15 Mhz 1
4 15 Mhz 1 30 Mhz 3
There meter on the transmitter showed the AGC level correctly.
The transmitter was switched on with the function switch, and the valves warmed up. It was connected to a 50 ohm dummy load. The meter showed the HT when switched to CW, and 10 watts output when the morse key was pressed. When switched to voice, and the MIC plugged in, the HT appeared when the PTT button was pressed.
An 80 m and a 40 m crystal were plugged in and the coils aligned. The drive appeared to be a little low, as indicated on the meter. The dummy load showed 10 watts output.
CONCLUSION
This is an interesting radio, as it shows the changing of technology. The receiver uses transistors and a printed circuit board. The transmitter uses valves and has point to point wiring. The modulator is transistorized, and the HT power supply uses transistors rather than a vibrator. It seems to work well. It is easy to use, especially the sensitive receiver.
REFERENCES
MTR1 MKII (AUST.) SERVICE MANUAL
MTR1 MKII INSTALLATION MANUAL
WIRELESS FOR THE WARRIOR Volume 4
Copyright
Ray Robinson