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omni30mmod [2017/04/29 12:51] n1ooq |
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| ==Building the bandpass filter== | ==Building the bandpass filter== | ||
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| + | Bandpass filter schematic: {{:schem_-_ind_coup_b.png?300}} | ||
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| The bandpass filter contains three wound toroidal cores. There are numerous instructions on winding available on the web. | The bandpass filter contains three wound toroidal cores. There are numerous instructions on winding available on the web. | ||
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| The T50-6 toroidal cores, with their windings: {{:img0014a.jpg?100}} | The T50-6 toroidal cores, with their windings: {{:img0014a.jpg?100}} | ||
| - | The cores are stacked on a piece of a zip-tie and hot-melt glued in place. A separation between the cores, about equal to their own width, is provided between them. | + | The cores are stacked on a piece of a zip-tie and hot-melt glued in place. A separation between the cores, about equal to their own width, is provided between them. The 15 uH inductor, with 59 turns, is stacked in the middle. |
| The cores, stacked and glued to a piece of a zip-tie: {{:img0016a.jpg?100}} | The cores, stacked and glued to a piece of a zip-tie: {{:img0016a.jpg?100}} | ||
| - | ==Adding the bandpass filter to the board== | + | The 56 pF capacitors are paralleled to total 112 pF, and the filter is wired as shown in the schematic. One side of the outer inductors is chosen as ground, and the taps are installed at the required number of turns up from this grounded end. |
| - | ==Adding the lowpass filter to the board== | + | |
| - | ===Testing=== | + | ==Building the 9 MHz trap== |
| - | Bandpass filter schematic: {{:schem_-_ind_coup_a.png?300}} | + | One T50-6 toroid is wound with 15 turns of #24 magnet wire. Target inductance is 1.0 uH for this toroid. This inductor is paralleled with a 270 pF, 50V capacitor and a 20-100 pF trimmer capacitor. |
| - | Bandpass board, bottom side, showing pads for 30m mod: {{:img0025a_-_edit.jpg?100}} | + | 9 MHz trap schematic: {{:9_mhz_trap_-_schematic.jpg?300}} |
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| + | The 9 MHz trap: {{:9_mhz_trap_-_photo.jpg?100}} | ||
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| + | ==Adding the bandpass filter and 9 MHz trap to the board== | ||
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| + | The stack is hot-melt glued to the bandpass filter board. It is attached vertically in approximately the same position as the Tentec transformer can for the original mod. There is a resistor which must be moved - see the Tentec instruction sheet. Both of these filters must be kept out of the way of the bandswitch shaft, which is nearby when the boards are re-installed in the radio. | ||
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| + | Bandpass board, bottom side, showing pads for 30m mod. At left, output. At the center, ground. At right, input: {{:img0025a_-_edit.jpg?100}} | ||
| Bandpass board, top side, showing finished 30m filter mod (between bandswitch and the shield can at the right): {{:img0032a.jpg?100}} {{:img0033a.jpg?100}} | Bandpass board, top side, showing finished 30m filter mod (between bandswitch and the shield can at the right): {{:img0032a.jpg?100}} {{:img0033a.jpg?100}} | ||
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| + | The 9 MHz trap is inserted in series with the input of the bandpass filter. On the prototype, it was hot-melt glued to an open area of the adjacent RX trimmer board, in such a way that the trimmer capacitor was easily accessible. | ||
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| + | Mounting location for the 9 MHz trap on the RX trimmer board: {{:img_1030_-_edit.jpg?100}} | ||
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| + | ==Adding the lowpass filter to the board== | ||
| Lowpass board, bottom side, showing pads for 30m mod: {{:img0019a_-_edit.jpg?100}} | Lowpass board, bottom side, showing pads for 30m mod: {{:img0019a_-_edit.jpg?100}} | ||
| Lowpass board, top side, showing finished 30m filter mod: {{:img0034a_-_edit.jpg?100}} | Lowpass board, top side, showing finished 30m filter mod: {{:img0034a_-_edit.jpg?100}} | ||
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| + | ===Testing=== | ||
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