As the title suggests, I am in the final stages of the design of a 4m transverter - the ARAC2. The circuits have been designed, breadboarded and tested as far as possible in that environment. The purpose of this post is to describe the project, and collect feedback and last-minute ideas before I commit the design to printed circuit. The timetable to complete the project is still a (hopefully small number of) months.
I will put the design (including PCB data files) in the public domain so anyone can build one or, more likely, groups of builders can arrange a joint project. Apart from the first batch of PCB for alpha builders/testers, I will not be manufacturing PCBs or kits. You should be able to send the design data (eg gerber file) to one of the online services in the UK or abroad and they will make the PCB.
Back in the 1990s, the Andover radio club ran a club project to build 4m transverters with apprx 5W output - the ARAC design. The idea was to encourage newcomers on to the band by giving them a pcb/kit to build, guidance on how to use ex-cb rigs as a driver, and a dipole design which could be built from DIY store bits. The design used commercially made coils, now unobtainable, and this is the primary reason it has lapsed. Somehow, I seem to have volunteered to do an update. Principally, I blame G4NNS (the original designer of the ARAC), plus an unremembered quantity of alcohol and general bonhomie at a microwave round table meeting. Ted, G3XUX, and the others who spend a lot of their time and effort running FM nets must also take responsibility.
The ARAC2 will follow the same principles as its parent. Additionally, avoiding obsolescence is a primary aim of the new design. There are pockets of 4m FM activity which will be a target audience, as well as clubs. The aim is to give them SSB/CW to expand their horizon. Chinese 10m transceivers can replace the cb radio of ARAC1, and many more people have FT8*7 or equivalents than in the '90s. We expect initial activity by many of these builders will be on vertically polarised SSB, perhaps as extensions to the FM nets that run regularly (that's the key word) in various places around the country. Vertical antennas are cheap to make or buy, simple to erect and have low visual impact; the FM community have them already. Once the bug has bitten, antennas can become horizontally polarised and expand to suit, rather than being required before contacts can be made.
This is not intended to be a cutting-edge, high performance design for dx-chasers. It will be as straightforward to build and set up as possible, and if that compromises the last bit of performance, then so be it. The design could be altered for 6m and probably 2m. Someone else can do that.
Here are the project aims in more detail:
Straightforward to build
Generous pcb dimensions and mostly through hole components.
Double-sided pcb with plated through holes. More expensive, but more repeatable performance. You could probably make a pcb with the laser toner method as one side is a ground plane.
A prepunched aluminium case is under consideration
As foolproof as possible to set up
Built in measurement circuitry for local oscillator setup, power output, and to indicate overload of the transmit mixer
Resistance to obsolescence
Inductors are air-wound, or on toroidal cores. Yes, the latter is betting on the survival of Micro-metals Inc, but I saw little alternative for larger values of inductance. Generous clearance around toroid locations allows future substitution if really necessary.
Mmics for amplifiers. There's a huge array of these from many manufacturers. They are relatively power-hungry, but dc power is easy to come by.
The transverter will produce about 100mW output. A power amplifier design on a separate board will provide about 18 watts output. A *possible* alternate PCB design will accommodate whatever you can find in the way of power transistors.
Multiple footprints for device substitution. Eg the mixers which can be the widely available SBL-1 or the newer standard for 6-pin SMD mixers.
Comments and ideas are welcome - please append to this topic, after my next post which has more details.
(continued in next post....)