|This review is, of necessity, somewhat lengthy, but considering the subject, this is inevitable.|
This is not a kit for the faint-hearted! It poses quite a challenge to assemble correctly and to get it working since it uses all surface mount components, which were originally intended for automated rather than manual assembly. Equally, although there are quite a number of pictures and other assembly information on the Juma website, there is no "Heathkit Style" assembly manual.
You should download every scrap of information, and print out the illustrated parts list for each module as well as the printed circuit board layouts and schematics. The boards are of high quality fibreglass with silk-screen printing and gold-plated pads. Component designators are marked on the boards, and the components are supplied in packets with the contents labelled. Resistors are marked with their value, but take great care with the ceramic capacitors, they are not marked, and they use different dielectrics for differing applications - do not mix them up - there is no way of identifying the dielectric types if you do. The NPO/COG dielectric is used for precision applications such as the polyphase networks, the X7R dielectric for ordinary coupling and decoupling purposes. The packets are marked, but only open and remove those components you are immediately going to install.
The order of assembly is, in some cases, important. Mounting certain components before others can make subsequent assembly very difficult. Study the boards and the photographs and work out where access might get restricted. If anyone would like further information I have prepared an illustrated PDF guide explaining some of the 'challenges' I faced, email me and I will forward it to you.
I found it best to tin all the pads on the printed circuit board first, and then remove the excess solder with solder wick. It made the assembly very much easier.
Total assembly time was of the order of 40 hours. It will require patience. Take frequent breaks, do not continue when tired, you will make a mistake. Although resistors and capacitors are fairly easily removed if a mistake is made, the same cannot be said for the semiconductors. Attempting to remove a misplaced IC without damaging it is almost impossible. Make absolutely certain that the device type and the orientation is correct before soldering all the leads in place.
You will need a good 40W - 60W temperature controlled soldering iron with a grounded tip, and an assortment of bits. I mostly used a 1.5mm chisel tip, but some things needed a better heat flow, and a 2mm and even a 3mm chisel tip had to be used. You will also need some tweezers, both the normal type and the reverse type. (Reverse tweezers are squeezed to open them - they grip without needing any pressure.) You will also need 0.38mm solder, anything thicker will prove difficult to use. Rosin mildy-activated flux (RMA Flux) is also required, as well as an assortment of sizes of solder-wick, from 1.5mm to 3mm. You might wish to consider purchasing the Juma SMD Starter Kit which contains solder wick, flux, tweezers, and solder.
It is essential to take appropriate electrostatic discharge protection measures, and for this you will need an anti-static mat and wrist strap. Do not even contemplate assembly without these items, you will almost certainly damage the semiconductor devices, especially certain FET transistors that do not have any intrinsic input protection diodes.
It will be almost essential to have a SMD tweezer adaptor for your multimeter in order to absolutely identify components prior to mounting them on the board. I used a SMD tweezer multimeter which was invaluable as it ensured that not only was I mounting the correct device, but that its value was correct, and it was functional. It can be very difficult to identify a bad component afterwards. In my case I discovered a bad ceramic decoupling capacitor, and although the circuit would probably have worked perfectly well without it, things could easily have been different.
After all this patience and work, what of the end result? First, before applying power to anything, it is essential to perform certain sanity checks with a multimeter. Make sure that there are no shorts on the power supply bus. Check the connections of the ribbon cables etc. In other words, be very careful and sure that everything is satisfactory before appplying power for the first time. The active filter assembly can be checked out on a logic breadboard with a power supply, audio signal generator and oscilloscope prior to assembly. The main controller module can be powered up with a set of grabber leads and a stabilised bench power supply to verify that it is working, but for the rest, they can only be checked when assembled.
In my case, there were two faults on initial power up. The display contrast adjustment would not work, and the receiver was completely dead. In both cases a missed solder joint was the culprit. The dead receiver fault required the use of my Tektronix digital sampling oscilloscope to find. Be aware that in event of a serious fault you might require access to some sophisticated test equipment to diagnose the problem.
Fortunately the microprocessor comes with the firmware and a boot loader already installed, so you do not have to program it yourself. By means of the built-in boot loader it is possible to update the firmware via the transceiver's RS-232 port. My firmware (Kit #98) was version 1.05, the latest version is 1.06. Since most modern PCs are no longer equipped with a 'real' serial port, it is common practice to use a USB to RS-232 convertor.
What you get is a nice simple 10W QRP CW/SSB all-band transceiver that only needs a 2.5A 12V power supply or small gell-cell and a QRP transmatch to get on the air with almost any reasonable antenna system. In my case I found the audio output somewhat low for its internal loudspeaker, but as I tend to use headphones anyway this was not a big deal. For speaker operation I use a set of PC speakers.
The receiver has more than adequate sensitivity, the minimum detectable signal being around -130dBm, and quite nice AGC characteristics. The AGC is always on, it cannot be turned off, although you can adjust the speed. On the bands from 160 through 20 metres, the number of spurious responses are low, and their levels, for the most part, at or below normal atmospheric noise levels, and thus pose no real difficulties.
On an unmodified transceiver, sadly, for the bands above 20 metres the situation is much worse. It is a fact of life that a Direct Digital Synthesiser will produce spurious signals along with the wanted one, and as its spurious-free dynamic range is less than that of the receiver, you will encounter various birdies, tweets, and noise artifacts, particularly in a direct-conversion system such as this. As the output frequency of the DDS chip approaches a significant fraction of the master clock, these artifacts increase in both number and amplitude, and an unmodifed transceiver is plagued with them above 20 metres. The designers have recognised this, and there is now available a small kit to neatly modify the receiver section to largely eliminate even these spurii. Anyone contemplating purchase of this transceiver would be well advised to get the Juma TRX2 Spur Elimination kit as well, as it vastly improves the performance of the receiver by elminating or greatly decreasing both the number and amplitude of the spurs. As a result, my modified transceiver works very well on all bands from 160 through 12 metres. 10 metres is still somewhat 'birdy' prone, but even on this band the improvement is such as to take it from the 'almost unsuable' to 'quite acceptable' category.
So how does it compare? I purchased the companion PA-100D 100W linear amplifier to go with this transceiver, and in Europe the combined kits cost a total of about 1,400 Euro, or about $1,700 at today's rates. On the one hand, if you are willing to spend around $1,700 then there are any number of compact 100W transceivers available from Icom, Yaesu, or Kenwood that have excellent receivers, as well as advanced digital signal processing and highly capable transmitters. If your main interest is a compact QRP rig, then the TRX-2 by itself is about 500 Euro without VAT or about $600, to which you would have to add shipping and handling as well as US Customs & Import duties and taxes. There are several commercial QRP rigs available in this price range as well, such as the FT-817 for around $650, so it faces stiff competition. What you get is the pleasure of building it yourself, as well as getting to understand exactly how it works, and also the ability to customise its operation if you are so inclined. It was these last two factors that tipped the scales for me, as I am a software engineer, well versed in the 'C' programming language, and the ability to customise its operation and that of the linear amplifier to any desired degree was a big plus. In the end, only you can decide whether spending this sort of money, time, and effort is worth the pleasure of having a unique product that certainly raises eyebrows wherever it is seen, and which puts out such a nice clean signal. To me, it is a little gem.
I have now modified the software to provide some enhanced facilities such as the ability to rapidly select any amateur band, as well as enhancing the accuracy and resolution of the synthesiser. Note, this is in no way an "official" release - use at you own risk. If you would like to try this new version, simply email me and I'll be happy to send you the latest revision.