Re-using the damaged PSU/Control unit was out of the question. The original design, on which I based my circuitry called for a relay to deliver the volts to the 10V regulator. I had replaced this relay with a high current MOSFET. In actual fact, there were two such devices in series since sequencing is provided by a DB6NT style sequencer. Each MOSFET has an on-resistance of only 60 milli-ohms. Without any extra heat-sinking, these devices are capable of dissipating around 1.5W. My calculations showed that the peak current would incur a peak power dissipation of around 3W, thus requiring a moderate heat-sink. This was achieved by mounting the devices at the board edge and wrapping two small sheets of copper over the edge to transfer the heat to the heat-sink. It isn’t very elegant but it works . . . the heat-sink gets noticeably warm, but no more than that.
PSU/Control PEC, underside.
. . . In contrast, the regulator heat-sink gets very hot since it is dissipating at least 25W. Thus a square aluminium pillar, insulated from the heat-sink is fitted between the finned heat-sink and the chassis to aid dissipation. Note the extensive use of surface mount devices.
PSU/Control PEC, topside.
The photograph on the right shows the finished transverter with the PA block and heat-sink mounted on the lid. A temporary S-shaped semi-rigid cable is used to link the output of the Ionica PA to the antenna change-over relay. When the box is closed, this cable is removed and a hole in the rear panel allows for the cable connecting the PA to the relay to be secured. The losses incurred as a result of the flexible cable between the DB6NT transverter and the PA can be ignored since a variable attenuator is already required to bring the drive level down to around 0.5mW.
I need a bigger shelf now! Left to right - 2m linear (80W), 4m (30W), 13cm (50W), 23cm (30W), 9cm (15W), 70cm (10W) and Bobby
With the demise of the Ionica box housing the planar-array, I needed a new antenna. Most people go for dishes at 3.4GHz but it gets very windy up here in GM so I looked for something with less
wind-loading. The RSGB Microwave Handbook describes Quad-Loop yagis for 23cm and 13cm as built by G3JVL and I concluded that a similar approach would work on 9cm using 1.6mm copper wire for the directors. So I simply extrapolated the dimensions which turned out to be very close indeed to G0RRJ’s own 9cm QLY. The driven element is made from a strip of copper fed through the boom by way of a length of semi-rigid coax. The actual feed-point is salvaged from an M-Squared 23cm yagi which was brought down in a storm (not mine!). I did say it gets windy up here! To protect it from the weather I sprayed it with two coats of what Halfords call
‘Appliance White’, and one coat of clear lacquer. Forget optimal spacing . . . The photograph on the right shows the antenna tucked in between the 70cm and 2m antennas. There is the possibility that it’s proximity to the 18ele parabeam will dissuade birds from perching on it. That’s my story, and I’m sticking to it . . . Hi! Hi!