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Version:

Oct 30, 2023:
Revised: v1.2

The TR-105 5W HF SSB Portable Manpack Transceiver

The TR-105 was a transceiver designed and built in New Zealand for Search and Rescue communications. any years ago, this radio was a routine sight in tramping parties as volunteers went out to search for trampers, tourists and hikers lost or injured in the dense demanding bush and mountain terrain in New Zealand.  

UPDATED Oct 2023

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


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. It's now a semi-autonomous quasi-government agency, the Civil Aviation Authority (CAA). After working there for about seven years, I resigned to live and work for several years in Fiji with our young family, Fiji is a beautiful group of islands in the South Pacific. Then along came the military coup...

However, 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. We managed about 150 of these TR-105 radios. In those days, the CAD workshops also located in Wellington did the routine maintenance and distribution.

First Glance

The AWA TR-105 had only recently been introduced into the Search and Rescue role when I arrived. SSB had been made a mandatory requirement in 1974 and the older AM-based SAR radio, the TR-3, had been forced into retirement.

The new TR-105 was the result of a design and build contract between the New Zealand Government and AWA. It was designed around 1975 or 1976 and manufactured locally in their factory in Porirua, near Wellington.

Figure 2 : This is the type of rough country where these transceivers were used. Looks nice in fine weather like this but swift changes in the weather could lead to problems for people ill-prepared for the bush.

The TR-105 was built into a solid yellow plastic case. It clipped onto a lower battery box (nine D-size batteries) and it was packed into a heavy duty yellow PVC or canvas-like rucksack. The radios made for SAR also featured an integral heavy metal boss on one side. This allowed a fold-down HF whip antenna to be used. In addition, the sets came with a dipole antenna complete with a thin but high quality coaxial cable feeder. This was connected to the pair of banana sockets on the front panel.  

A cover could be clipped over the front panel of the radio to protect the controls. It also allowed the (staggeringly ugly) hand microphone and cord to be tucked away in a tidy manner. 

Figure 3 : 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.

(A possum is a furry pest that carries bovine TB. Clothing is made from their fur mixed with fine wool. Incredibly lightweight and fantastically warm)

A number of TR-105 transceivers were also made for Mountain Radio Service, an organisation run by climbing and hiking clubs around New Zealand. These were not fitted with the metal boss and whip antennas were not used by MRS. Members of the public who were planning to go into bush areas could hire one of these radios from MRS for a modest sum. They could stay in touch with MRS volunteers at regional bases in nearby towns, and any urgent issues could be promptly handled.

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 pressed on an insulated metal tab on the internal chassis which was wired internally to the transceiver PCB.

The front panel  featured controls for channel selection, volume, receiver fine tuning ('clarifier'), the internal antenna tuner, and a pushbutton for tuning. This button activated a distinctive two-tone oscillator inside the set. The internal ATU could then adjusted for the highest tone pitch. The panel also contained two red LEDs which were used as a simple battery meter. The original design was found to be somewhat inaccurate. A modification to the SAR radios improved this slightly, but it was never considered very accurate.

These radios were, for the time, relatively compact but complaints were routinely received about its onerous 4.5kg weight (with batteries) and its substantial size (190 x 90 x 270mm).



Figure 4 : No, this is NOT a TR-105. This is the much older Teleradio TR-3, an AM transceiver that was later replaced by the TR-105 SSB transceiver. The TR-3 is often seen in the results for internet searches for the TR-105 and in a few articles about the TR-105. However, the panel, radio dimensions and packaging seen here are all very specific to the TR-3. The TR-105 NEVER used a separate battery box.


Influences over the TR-105 Design

Designing a portable SSB transceivers was, and is, quite demanding. My notes from the time and subsequent research shows this was a very well understood field. HF radios were volume sellers at that time, and in the commercial portable or manpack niche market, a leading product  was the Spilsbury SBX-11 transceiver. Over 10,000 of these radios were ultimately sold, mostly in Canada. A number of other companies sold products into their domestic market e.g. Anritsu with their SS120 manpack in Japan.












Figure 5 : The market-leading Canadian-made Spilsbury SBX-11 may have influenced some aspects of the design of the TR-105


By the way, 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 intrigued by both the basic TR-105 design approach as well as some of the specific component choices made by AWA. It made for an interesting series of casual discussions over coffee.

In New Zealand at that time, HF SSB transceivers were the subject of a plethora of designs. An indication comes from the national amateur radio magazine, 'Break In'. There were designs for a number of compact transceivers for this type of application, particularly from 1968 through to 1975. There were also serious design articles on topics such as mixers and the impact of AGC on blocking and intermodulation.

A few of these significantly impacted HF design thinking in the country. One such as the "Solid state circuits for SSB" series by J W Herbert ZL2BDB which highlighted the importance of double balanced diode mixers as first receiver stages and benefits from high frequency (i.e. 5 - 9MHz) IF SSB filters. Others of the time also included designs by Peter Johnson ZL4LV and others in Dunedin, and, more importantly for our story, Bert Shuttleworth ZL4IO and others in Invercargill. (Many of these were professional engineers working for government departments for whom these designs were part of their hobby)

In 1971, Bert ZL4IO designed and published the detailed design for a compact 5W PEP three band SSB transceiver, the "Southland Companion". It operated on 80m, 40m, and 5680kHz for SAR use. It identified all of the technical background to the design and described how to build it. Interestingly, the article also mentioned (pg 376) that 'Advice was sought from AWA Ltd for the most modern and suitable transistors, ICs and other devices in the most favourable price range...". AWA was the designer and manufacturer of the TR-105 a few years later. Unfortunately, this wealth of technical design detail and field experience appears to have been unknown to the TR-105 design team.



Figure 6 : The design details of other similar compact
QRP SSB transceivers for the 3 - 8MHz range
had been recently published in New Zealand

The details of the ZL4IO transceiver design can be downloaded here. (Note: 9MB PDF) It worked very well although it's not a design you would build today given its high gains and numerous single sided PCBs.

Elsewhere in the amateur radio market around this time, the low power Yaesu FT-7 amateur radio transceiver became very popular. Like other Japanese transceivers of the time, it used the SN76514 balanced mixer instead of the almost universally used MC1496 chip. unfortunately, while the MC1496 is still around (It's not desirable these days at all!), the SN76514 quickly became obsolete and impossible to source.





Figure 7 : The Yaesu FT-7 transceiver also reflects engineering design thinking of the time




TR-105 Technical Detail

The TR-105 design followed a conventional approach with a single conversion superhet receiver and matching transmitter built around a 1.4MHz carrier oscillator and UK-made lattice SSB filter. Unusually, the TR-105 featured a number of Motorola MC1350 high gain balanced RF amplifiers throughout the design, including, very oddly, in the crystal oscillator.

Other radios of the time used far less costly discrete transistors and MOSFETs. There was minimal impact on final cost with this MC1350 choice, but using a series of these along with other high gain blocks was an invitation to potential signal overloading and/or RF instability. And, as noted earlier, this was very well known at the time.

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 using this 40841 MOSFET, along with a SN76514 for the transmitter balanced modulator.

The rest of the transmit chain used a 40841 MOSFET and a  pair of 2N2218 transistors to buffer the transmit RF signal.

Figure 8 : Top view of the transceiver with the channel oscillator with two crystals fitted (right hand side), the receiver mixer (lower left below the crystal filter), and the transmitter power amplifier (upper left)

This 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 and relatively expensive.

Arguably, should replacement be required, a pair of low cost 2SC1971 transistors, popular in many later low cost CB transceivers, could be a good choice. The mounting arrangement would require changes due to the TO-220 packaging, but the addition of a couple of feedback components at the same time would significantly improve the linearity of the power amplifier.

You can just make out the final transistors in the upper-centre left of the photo (Figure 8) above. The diode which adjusts the operating point of the PA stage is clipped to one of these transistors.

For those interested in further detail, you can download a copy of the service manual for the TR-105 here. FYI: It's a 13Mbyte PDF file.

Operational Use

While the TR-105 was capable of operating on up to six channels, only two HF channels were fitted and used in these radios in New Zealand. The MRS sets were fitted with two 3MHz channels while the SAR radios were fitted with 3023 kHz and 5680 kHz, notionally for night and day communications respectively. Initially, the SAR TR-105 sets were fitted with slightly different frequencies during the initial deployment to avoid interference with the existing AM TR-3 radios.

Later, all of these SAR TR-105 radios had to be recalled for a subsequent 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 and taken away for the usual bulldozer disposal process. I was able to keep a few of those surplus crystals doe my parts box with the approval of my bemused bosses. 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 (SAR sets only) and the light but sturdy dipole antennas supplied with the TR-105 were very well made. However, asking climbers and hikers using these radios to use the dipole rather the whip where possible in the rough rugged bush and alpine terrain of New Zealand while searching for missing people 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 very difficult indeed. 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.

An "aerial tune" control is located on the front panel. This adjusted a series-connected variable inductor. This can be seen in Figure 9 at centre-left. Probably added for tuning the whip antenna, the tuner also has a minor benefit for other types of antennas.


Figure 9 : The main PCB can be folded out for testing and alignment. It also reveals the adjustable inductor used to match some antennas.

Note: This radio has had over 40 years of service. The front panel was covered in mud (I chose it from the pile for that reason) and the battery box was corroded in spots. But inside, it is like the day it came out of the factory. And it met or exceeded every one of the manufacturer's specifications.

Let's see you take a modern low cost HF transceiver from South Asia, and use it for a year in rough terrain, bouncing around in a 4WD for example. Periodically, run the garden hose over it for several hours, dip it in mud, pop it in the freezer for an hour, and hose it off again. After a year, test it. Still working? The TR-105 still does that today with a smile on it's face!

Operational Experience

I have no direct experience of the design and development phase of the TR-105. That occurred before I arrived on the scene. What I inherited was a large fleet of radios with what ultimately became some commonly occurring problems. However, recall that these radios were intensively used in extreme climates and often endured very high levels of vibration. The users were not familiar with radio equipment and the treatment waded out to these TR-105 transceivers could be severe. Some probably got drowned in rivers, too, the water tipped out, and then the transceiver would just carry on being used.

It's of little surprise that:

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. Actually, their use was common practice at the time, these being all that was available. Good linear HF devices were still at least five years away. In hindsight it is no surprise that these devices broke into oscillation (due to excessive gain at HF), and that transmitter linearity was marginal.

None of these issues were show-stoppers and the discrete construction meant that you could actually find the components in the radio with ease and replace them. most are available from domestic parts resellers (if they exist near you!)  These days, the TA7358/LA1185/AN7205 (same IC, different part numbers) could be used to replace the SN76514, and a number of modern low cost transistors can replace those in the transmitter power amplifier. These would also allow the use of better feedback around the PA to give better linearity. Yes, the MC1350 is becoming harder to find, but it is still available.

Despite these issues, and in hindsight they were relatively few, the radios had a lengthy service life, later to be replaced by the much smaller Condor and the SR-3 transceivers. However, the increased availability of VHF and cellular services coupled with satellite and GPS equipment ultimately led to a reduced use of HF radio in New Zealand's mountains and bush. Despite this, the TR-105 lives on in a few locations providing useful low cost communications where these other services cannot reliably reach.

TR-105 Decommissioning

When the TR-105 reached the end of its life for Search and Rescue, it was replaced by the Condor and/or Codan 8332 transceiver. Later still, it was in turn replaced by the SR-3 transceiver. These are much lighter radios (to the 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 10 :  No, this is NOT a TR-105 either. This is the later Condor HF SSB transceiver which replaced the TR-105. It's a much smaller and lighter radio with a lower 1W PEP output power which used the phasing SSB method.




The Condor/Codan lower power (1W PEP RF output) design was based in part on the development of a series of specialised "hybrid" circuits, sub assemblies 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. I have also written a series of web- pages to the technology used and the conversion of these transceivers to amateur radio use on 80m and 40m.

Converting the TR-105 Transceiver for 80m and 40m Amateur Radio Use

Details will be released shortly on how the TR-105 can be modified for use on the 80m and 40m bands. The transceiver is expected to have the following features:

•    3.50 – 3.75MHz (80m) and 7.00 – 7.30MHz (40m) tunable coverage (60m optional)
•    User programmable high and low band VFO tuning limits
•    User programmable start-up/power-up frequencies for each band
•    Selectable VFO tuning rates – 10 and 100Hz, 1 and 10kHz steps 
•    SSB (A3J) with optional automatic USB (60m) and LSB (80m) mode selection
•    Full 6-digit OLED frequency display with 10Hz resolution i.e. 3.684.53 MHz
•    OLED tuning step indicator of currently selected tuning rate
•    S-meter bar-graph display
•    Battery level meter (on OLED display)
•    Power switch with audio volume control
•    Band selection switch
•    Tune test tone pushbutton
•    Tuning lock button (Lock mode status icon appears on the OLED)

•    Rx sensitivity: Better than 1uV for 12dB SINAD
•    45 dB adjacent channel rejection
•    Tx: 5W PEP output
•    40dB carrier attenuation
•    40dB opposite sideband attenuation

•    10 - 15V (9 x AA-cell) internal or external supply range
•    Rx: 90mA Tx: 500mA (speech)
•    190 x 90 x 270 mm
•    4.5 kg (with batteries)


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 and then gave us a wide range of challenging, interesting and valuable experience. Many 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. Recently I was given one to convert to the 80m and 40m amateur radio bands using my popular SugarCube VFO. I will add some pages here soon on the details of the process.

Keeping these radios operating successfully for SAR use 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. Now, I hope, I can take a modified TR-105 back into a remote part of the country and enjoy operating the radio myself.

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