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May 7, 2021:
Revised: v1.0

The AWA Teleradio TR-105 

5W HF SSB Portable Manpack Transceiver

Many years ago, this radio was a routine sight in tramping parties as volunteers went out to search for lost trampers and hilkers in the dense demanding bush and mountain terrain in New Zealand.  

Introduction

When I graduated from university as a young telecommunications engineer many (many!) years ago, I began work in the HF Radio section of the Civil Aviation Division (CAD), a part in those days of the Ministry of Transport. Now, of course, civil aviation is managed in New Zealand by a semi-autonomous quasi-government agency, the Civil Aviation Authority (CAA). I left CAD many years ago, moving on to work for several years in Fiji, a beautiful group of islands in the South Pacific. Then along came the military coup...

Anyway, as a young radio engineer in CAD back then, the odd jobs naturally fell onto my desk. One of those tasks was providing technical support for the maintenance team handling the radio equipment used for search and rescue around New Zealand. If memory serves, I think we had about 150 of these TR-105 radios. In those days, the CAD workshops also located in Wellington handled the routine maintenance and distribution.

First Glance

This radio was designed and manufactured locally by, in those days, the multi-national company, AWA, at their factory in a nearby light industrial suburb of Wellington.


Figure 1 : The TR-105 was a crystal-controlled 5W PEP HF SSB transceiver packaged in a rugged bright yellow ABS plastic case.

A cover could be clipped over the front panel of the radio to protect the controls and to keep the (staggeringly ugly) hand microphone and cord from flapping around. It also could hold the dipole antenna. On the rear, a clip-on battery pack containing nine D-cells was mounted onto the base of the radio.

The TR-105 was carried in a heavy duty
yellow PVC rucksack along with a fold-down whip antenna. The dipole antenna complete with its thin but high quality coaxial cable also usually found its way there. It was (for the time) relatively compact but complaints were routinely received about its onerous 3kg weight. Few, if any, of the PVC bags exist today.


Figure 2 : Here's a rare photo of one of the original TR-105 radios sitting in its PVC pouch during operational use complete with the manufacturer's logo. Yes, advertising the company to observant possums living in the depths of the New Zealand bush was clearly seen as important back in those days.


In use, the whip antenna could be slid into the metal clamp mounted onto one side of the TR-105 main plastic case. This clamp was wired internally to the transceiver PCB.

Typically, however,, the dipole antenna was used. It was connected to a pair of banana-type plastic screw terminals on the front panel. The front panel also featured controls for channel selection, volume, receiver fine tuning ('clarifier'), the internal antenna tuner, and a pushbutton for tuning. This button activated a hideous sounding two-tone oscillator inside the set. The internal ATU was then adjusted for the highest tone pitch. Quickly. That sound could wake the dead.

The TR-105 replaced the earlier AWA TR-3, an AM radio. While many TR-3 sets were still quite serviceable (and a few went on to be used for a number of years in very remote locations such as Campbell and Raoul Islands for local communications for island-based CAD and Met Office staff), international regulations required the migration of such services from AM to SSB. That was the key driver for the development and deployment of the TR-105.

Incidentally, a radio often pictured on the web as a TR105 is actually a great example of the older TR-3 AM transceiver. The TR-105 NEVER used a separate battery box.




Figure 3 : No, this is NOT a TR-105. This is the much
older AWA-made Teleradio TR-3, an AM transceiver
superceded by the TR-105 SSB transceiver.


AWA engineers apparently based much of the conceptual design of the TR-105 radio on the highly successful Spilsbury SBX-11 radio. At least, that's what they led me to believe. Internally, the radios are also constructed along similar lines, too. The SBX-11 four-channel capable design with its similar performance specifications was to all accounts a better design.
Component choices in the SBX-11 were also based primarily on design requirements. The effective design of that radio also seemed led to its very successful sales record, something not matched by the TR-105.

When I met the Spilsbury designers some years later in Canada, long after production of both radios had ceased, this topic came up in conversation. I recall them being quietly bemused over both the basic approach as well as some of the specific design decisions made in the TR-105. It made for an interesting series of casual discussions over coffee.












Figure 4 : You might easily mistake the Canadian-made Spilsbury SBX-11 for a TR-105 with very good reason



Operational Use

While the TR-105 was capable of operating on up to six channels, only two HF channels were used in these SAR radios in New Zealand. One channel was set to 3023 kHz, the other operated on 5680 kHz, notionally providing night and day communications channels. Initially, the TR-105 was fitted with slightly different frequencies during the initial deployment to avoid interference with the existing AM TR-3 radios.

Later, all of these TR-105 radios had to be recalled for the necessary frequency change. With 150 radios and two crystals to be changed in each set, I ended up with 300 crystals in a big cardboard box next to my desk. They lived there for some time until they were written off by the government's auditing staff. I still have a few of those surplus crystals in my parts box of the handful I was permitted to rescue from the otherwise inevitable bulldozer destruction method used by government departments for such items. I made numerous ladder crystal filters from them, and a few are still working just fine in a couple of radios sitting on my shelves.

The military-style collapsible whip and the light but sturdy dipole antennas supplied with the TR-105 were very well made. However, asking trampers, the folk usually required to carry these radios into the rough bush and alpine terrain of New Zealand while searching for missing people, to use the dipole rather the whip, where possible, was often a lost cause. The whip was much faster and easier to put up in the bush. Unfortunately, it just didn't work as well as the dipole.

To be fair, using the much better performing dipole was often a complete nightmare. Pulling the dipole wires through dense bush to get some height over the terrain, pulling back the coax to the radio, then dragging it all down again after the call was completed, could take a massive effort. In the rain and snow, it was absolutely no fun at all.

I have no direct experience of the design and development phase of the TR-105. That occured before I arrived on the scene. What I inherited was a large fleet of radios with a series of routinely occuring problems.

Later, a number of parts became increasingly difficult to find. The transmitter power amplifier transistors were particularly problematic. These were basically VHF FM power transistors used in the TR-105 on HF for SSB service. Looking back, it is no surprise that these devices broke into oscillation from excess gain, and that transmitter  linearity was marginal. Still, to be fair, there were few better options available back in those days so far as I recall. Fortunately, the maintenance team were experts at keeping these radios going, for many years.

Despite these issues, the radios had a lengthy career in service. Some are still in use(!), as mountain safety radios for casual hikers and trampers, for example. The increased availability of VHF and cellular services coupled with satellite and GPS equipment has led to a reduced use of HF in New Zealand's mountains and bush. However, HF continues to be useful where these other services cannot reach.

Technical Detail

The TR-105 design followed a convertional approach with a single conversion superhet receiver and matching transmitter built around a 1.4MHz carrier oscillator and UK-made lattice SSB filter. The MC1350 IC, a 50dB gain-capable amplifier with 60dB AGC range, was an interesting and novel (!) choice for the receiver front end. The same device was also used as the multi-crystal channel oscillator (!!). More conventional use was made of the device in the tx/rx IF chain, along with a 40841 MOSFET.

The transmit chain featured a speech compressor in the microphone amplifier, again using a 40841 MOSFET, and a SN76514 was used as the transmit balanced modulator. The SN76514 quickly became another
"Near Unobtainium" component for this radio.

The remainder of the transmit chain used a 40841 MOSFET along with a conventional pair of 2N2218 transistors to buffer the transmit RF signal.

That transmit signal was then fed to the final power amplifier consisting of a pair of 2N5992 (which Motorola suggest is equivalent to the MRF232) or 2N5642 power transistors. These are notionally 10W or 20W capable VHF FM power transistors. The final power amplifier stage design and layout was typical of the period, and, as noted earlier, achieving specified SSB linear operation was a continual challenge. You can just make out the final transistors in the upper-centre left of the photo above. The diode which adjusts the operating point of the PA stage is clipped to one of these transistors.

For those entertained by such things, you can download a copy of the service manual for the TR-105 here. FYI: It's a 13Mbyte PDF file.

Replacement

When the TR-105 reached the end of its life for Search and Rescue, it was eventually replaced by the Condor and/or Codan 8332 transceiver (Different branding for the same transceiver, I believe), and still later, the SR-3 transceiver. These are much lighter radios (to the likely delight of the trampers having to carry them). Interestingly, the Codan/Condor radios used a phasing SSB approach rather than the filter method used with the TR-105 and most other radios of the time.


Figure 5 :  No, this is NOT a TR-105 either. This is the later Condor HF SSB transceiver, a much smaller and lighter radio with lower output power featuring improved reliability. It replaced the TR-105.


I understand the Condor/Codan 
lower power (1W PEP RF output) design was based in part on the development of a series of specialised "hybrid" circuits, subassemblies built from SMD-like parts on a ceramic substrate, by the (then) Department of Scientific and Industrial Research (DSIR), in Wellington, New Zealand.

An article describing some of the background to the design process for such a compact SSB phasing transceiver
along with some of the circuit details can be downloaded here.

Conclusions

I still think back positively to this time early in my engineering career. In those days, government departments hired many young graduate engineers from university, providing us with a wide range of challenging, interesting and incredibly valuable experience. Many of those engineers went on to hold key positions in the industry in and beyond New Zealand.

The TR-105 continues to hold some special memories for me. One day, I may acquire one myself, just for old-times sake. It was an interesting radio to work on with some novel
design features, a few being fairly doubtful, and not all of them entirely successful.

Finding optimal solutions to keep them operating successfully was a learning experience for me. Even today, the glimpse of a bright yellow backpack or radio out in the bush brings back the memories of those days and this radio.




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