09-13-2008, 07:59 PM
Some sets go with the LO below the fundamental on the top band. There's no rule-of-thumb and no easy way to tell in advance. Plus I don't think I've ever seen any alignment instructions that would give a specific clue. Some will advise that there may be two peaks on the trimmer and to use one or the other.
Most radios will readily peak on either side AT the upper end alignment frequency on the top band. Image rejection on most consumer radios really stinks up there. But it will generally be obvious in tracking towards the low end if you have hit the incorrect peak.
That RCA that I recently did, Brian, was a classic case. It didn't align particularly well either way.
EDIT - an additional thought. I suppose a guy could sit down with a counter (or digital radio) and measure the LO at various points across the band compared with the dial - adding or subtracting the IF accordingly. One set of measurements *should* line up better than the other against the dial readout. I've never taken that approach and quite frankly some radios might be too poorly calibrated to tell but it might give a clue as to which injection side shows the most promise. -
Most radios will readily peak on either side AT the upper end alignment frequency on the top band. Image rejection on most consumer radios really stinks up there. But it will generally be obvious in tracking towards the low end if you have hit the incorrect peak.
That RCA that I recently did, Brian, was a classic case. It didn't align particularly well either way.
EDIT - an additional thought. I suppose a guy could sit down with a counter (or digital radio) and measure the LO at various points across the band compared with the dial - adding or subtracting the IF accordingly. One set of measurements *should* line up better than the other against the dial readout. I've never taken that approach and quite frankly some radios might be too poorly calibrated to tell but it might give a clue as to which injection side shows the most promise. -
