06-25-2013, 02:53 PM
Hello all,
Here is the rundown. While waiting for parts I swept the RF, LO and IF tuned circuits. Normally I can thet the allignment about 90% this way. On this radio the IF is published as both 450 and 460 khz. As found the IF on this one could not be tuned there. The caps simply would not go low enough in value. About the middle of the useful range put the IF at about 250 khz. The RF and LO could be adjusted 455 khz apart but it was all the adjustments could do. Assuming the IF of 250 khz I went ahead and alligned the radio and it works fine, quite well actually. The bottom half of the band is pretty quiet. Our most powerful stations are in the top half so I am not sure this is a problem. I am thinking the next step is to use the signal generator and check the sensitivity across the band. One possibility is that the RF and LO are diverging toward the bottom of the band. I'll do some checking.
The big question is the accuracy of the published IF frequency. Has anyone alligned one of these to 455 khz IF or seen a published IF in the 250 khz range? Any enlightenment would be appreciated.
keithw
Here is the rundown. While waiting for parts I swept the RF, LO and IF tuned circuits. Normally I can thet the allignment about 90% this way. On this radio the IF is published as both 450 and 460 khz. As found the IF on this one could not be tuned there. The caps simply would not go low enough in value. About the middle of the useful range put the IF at about 250 khz. The RF and LO could be adjusted 455 khz apart but it was all the adjustments could do. Assuming the IF of 250 khz I went ahead and alligned the radio and it works fine, quite well actually. The bottom half of the band is pretty quiet. Our most powerful stations are in the top half so I am not sure this is a problem. I am thinking the next step is to use the signal generator and check the sensitivity across the band. One possibility is that the RF and LO are diverging toward the bottom of the band. I'll do some checking.
The big question is the accuracy of the published IF frequency. Has anyone alligned one of these to 455 khz IF or seen a published IF in the 250 khz range? Any enlightenment would be appreciated.
keithw
