Wednesday, February 22, 2012

The HX Files 019


Hello and welcome to Xtract 19 of the HX Files.
In this Xtract.
 A new 23cms transceiver for the shack.
 I would like to talk about this project that was made for use as a base transceiver; this project would be a 60 watt ATV transceiver for 23cms. The first thing to do was to get a project box that was not just big enough, but structurally  strong enough, so with safety hat on a suitable one was dug out of the stores bunker, as well as a suitable heat sink for the amps. The heat sink was originally an amp for a mobile phone system that was in the stores bunker for a couple of years, the inside was stripped out of its components, some of them for the skip, and some for the stores department, the heat sink was found to be only a couple of mm shorter than the project box and it was exactly the same height as it. The project box purchased was a used piece of scraped test equipment with most of the original parts removed before sale, after looking at the back of the box and at the heat sink that was going to be used, it was decided to use part of the original back panel (photo 1 below )as this would help with the fitting of the heat sink.


After a bit of measuring and marking, a small precision cutting device was to remove the centre of the panel, (A 100mm angle grinder). The rest of the panel was lined up with the heat sink and both marked for drilling some mounting holes. When lining up the panel up with the heat sink for drilling, care had to be taken that the holes to be drilled would be between the fins of the heat sink and there would be no need to remove any of the heat sink. Thanks to a bit of time spent placing the parts and a bit of measuring, the holes were drilled, they were close, but luckily there was just enough space to add the washers and nuts. The panel was then removed so that there was room to place the 2 amps on the heat sink, a couple of paper templates were made of the mounting holes of the amps to mark out the spots on the heat sink that were to be drilled but no matter were the templates were positioned the holes would be over a fin of the heat sink, so as the heat sink was 8mm thick the holes would be drilled to a depth of 6mm and then be taped. Thanks to Michael EI 5 GG for the master class in the use of his pillar drill and taps, and a couple of hours later the job was done. The amps were placed on the heat sink temporally and were wired up and a few tests carried out making sure they were giving out their full power, and after 1 hour on transmit the heat sink was still cool enough and more than likely it would not be transmitting for that amount of time in one go again. As the heat sink worked so well during the testing, no fans were to be used in the final design, and with that job done the back of the unit was refitted to the box. A chassis for mounting all the various parts that would be used was made from a piece of a scraped metal that once was the top of and old PC table, this had a couple of benefits as It was the type that had the perforated top, and the holes could be used for mounting the various parts, and it would also aid in air circulation. The amp requires a voltage of 24 volts at 4 amps, but the other parts like the 2 watt driver amp, the RX/TX boards, relays and various lights, would only need 12 volts to power them. I was toying with the notion of using 24 and 12 volts from external power supplies, this would not be a problem as the unit would be a base transceiver, but to go portable and having to bring a couple of power supplies was not on, so a 240v AC to 24v DC PSU was fitted into the case (photo 2 below).














 As the PSU had two separate lines out for 24volts, plan A was to use a voltage regulator I had that would drop the 24 volts to 13 volts and it would be able to handle 6 amps which was more than I needed, but I had to go with plan B as I could not find the amp. So plan B was to use a couple of smaller voltage regulators for each of the TX/RX boards to take the voltage down to the required volts, the regulators were mounted on a small heat sink that would keep them like the Fonz (cool) seen on the bottom right of photo 3 below .

The power supply used was one mentioned in a previous HX file that was purchased at a rally last year, and the fact it also had a fan installed to help with it’s cooling was not a bad thing, it has a few taped mounting holes around it’s body so using a couple of bolts of the same thread and after measuring it, a couple of holes were drilled in the side of the unit and the PSU was bolted to it.





 The PSU was placed on its side (photo 4) as doing this would leave more room in the box for the other parts. The TX/ RX boards, preamp, coaxial relay and the other parts were dry fitted in various locations until I was happy with the layout.
 Another benefit of having a perforated chassis meant I would be able to hide some of the cables, the holes could be made wider with a reamer and you could install grommets in the holes if needed so you would be left with smooth edges and not run the risk of any of the leads chaffing. The front panel was cut from a piece of an old aluminium sign, the panel would be strong as it is 3mm thick, and the it would be 312mm wide and a height of 105mm, that’s around 12”x4” in old money. The metal sign that was to be used for the front panel, was not in great condition as it had a few marks and scratches on it, so when all the drilling is finished, some sticky back plastic (well if its good enough for Blue Peter then its good enough for me) would be used, as it comes in various colours and finishes. But before all that the first thing to do was to try a couple of designs to see what want were, after the final design was chosen it was held onto the front panel with masking tape (photo 5 below                                                                                                     

The drill points marked with a punch, and after a bit of care the holes were drilled first using a 3mm drill bit and then finished off with the right size drill bits, and with the use of a file and a reamer the panel was finished, the parts were fitted on the panel and then removed to be able to apply the plastic covering. 








 As you can see in photo 6 on the left,the finished front panel with all the fittings installed. Having the back panel free of any fittings would mean that the transceiver could be placed close to the shack wall, and due to the tests carried out earlier, (it not needing any cooling fan(s), and with the carrying handles it would also mean some type of protection for the front panel. As I mentioned earlier this project would be a base unit, but if I did decide to go /P with it I would need a DC to AC converter to take the 12 volts DC to 240 volts, and as I did not want to bring a generator. That’s it for this issue of Echo Ireland, and if you would like to see other pictures of the build you can go to my blog, thehxfiles.blogspot.com.. Below is some more photos of the build.

And finally,  that may all your signals be P5. 73’s Pat.



Early layout














Final parts layout



Some tidying up left to do

No comments:

Post a Comment