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omni30mmod [2017/04/29 14:10] n1ooq |
omni30mmod [2017/04/29 17:18] (current) n1ooq |
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| *1x - 20 to 100 pF trimmer capacitor, mica compression, Arco 406 or equivalent | *1x - 20 to 100 pF trimmer capacitor, mica compression, Arco 406 or equivalent | ||
| *about 45 inches - #18 magnet wire | *about 45 inches - #18 magnet wire | ||
| - | *about 40 inches - #24 magnet wire | + | *about 50 inches - #24 magnet wire |
| *about 40 inches - #32 magnet wire | *about 40 inches - #32 magnet wire | ||
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| 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. | 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. | ||
| + | ==Building the 9 MHz trap== | ||
| - | ==Adding the bandpass filter to the board== | + | 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. |
| - | 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. | + | 9 MHz trap schematic: {{:9_mhz_trap_-_schematic.jpg?300}} |
| - | Bandpass board, bottom side, showing pads for 30m mod. At left, output. At the center, ground. At right, input: {{:img0025a_-_edit.jpg?100}} | + | The 9 MHz trap: {{:9_mhz_trap_-_photo.jpg?100}} |
| + | ==Adding the bandpass filter and 9 MHz trap to the board== | ||
| + | |||
| + | 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. | ||
| + | |||
| + | 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}} | ||
| - | ==Adding the lowpass filter to the board== | + | 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. |
| - | ===Testing=== | + | Mounting location for the 9 MHz trap on the RX trimmer board: {{:img_1030_-_edit.jpg?100}} |
| + | |||
| + | ==Adding the lowpass filter to the board== | ||
| + | The lowpass filter is built directly on the lowpass filter board. The two inductors are wound from #18 magnet wire - 16 turns, close-wound over a 5/16-inch drill bit. The target inductance is 0.9 uH for both inductors. 1000V capacitors are used in the filter, as it will be handling the full output power of the rig. There is a jumper wire which needs to be removed - see the Tentec instruction sheet. | ||
| 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. Right, a 330 pF cap. Center, a 560 pF cap. Left, a 270 pF cap. The 2nd leg of the caps is soldered to the ground plane on the top side of the circuit board, as directed on Diagram 1 of the Tentec instructions. Near the center, the two inductors : {{:img0034a_-_edit.jpg?100}} |
| + | |||
| + | ===Alignment and Testing=== | ||
| + | |||
| + | A general-coverage receiver with a BFO will be needed for alignment of the 9 MHz bandpass filter. Adjust the capacitor with a non-metallic tool only! A metallic tool will introduce a large amount of noise into the circuit, which will pass directly to the power amplifier. Adjust for minimum signal at 9.000 MHz. The rig may or may not need to be connected to an antenna, and may or or may not need to be transmitting (at low power) to hear the signal. This is the only alignment required. Bring up power slowly, with an eye on the SWR meter. High SWR into a resonant antenna or a tuner is an indication that the filters are not working properly and large spurs are being transmitted. With the general coverage receiver, listen to the 2nd harmonic at 2x the transmitted frequency. It will probably be audible, but should be relatively weak. | ||
