17 Meter Switched VXO Frequency Modification |
The 17M V.2 Radio covered a nice portion of 17M from about 18.120 to 18.144 MHz and many contacts were made within this narrow range. It soon became apparent that to get a greater range would require additional crystals on a frequency other than 11.520 MHz. I ordered custom crystals from ICM on a frequency of 11.535 Mhz. Using this frequency would give coverage on the higher portions of the band with specific coverage of the hfpack frequency of 18.157.5 Mhz. I wrestled with the problem of trying to find a way of switching between the two VXO ranges. I wanted to keep the leads as short as possible yet have a front panel control to switch between frequencies. That is when I hit on the idea of a small DPDT dip relay that would switch each set of crystals completely out of the circuit. a small panel mounted DPDT switch energizes the relay. The second set of contact will be used to light small LED to indicate what frequency range the radio is on. With these two sets of crystals the radio now covers 18.122 to 18.144 MHz and 18.150 to 18.168 MHz. There is a small 6 KHz gap that is not covered. By juggling other circuit parameters that gap can be narrowed at the expense of reduced overall coverage. |