Re: Stock Sangean DT-400W Receives 6 TP's at Grayland
Thanks for your suggestion about a possible 1400 kHz trimmer adjustment procedure for the DT-400W.
As we recall, when you developed your DT-200VX alignment procedure, on the DT-200VX RF board the 1400 kHz trimmer and AM IF transformer adjustments are just barely accessible in the operating configuration (with the 14-lead plug in jack between the RF and digital circuit boards just barely making contact, as the boards are separated enough to provide access to the two adjustments). On the DT-200VX, both of these adjustments have a "hair trigger" adjustment tendency, in which slight changes throw the whole AM alignment seriously out of the optimum position.
On the DT-400W, however, the RF board has been completely redesigned, with the 1400 kHz trimmer and AM IF transformer adjustments relocated to a completely inaccessible position whenever the 14-lead connection jack has continuity. As such, these hair-trigger adjustments cannot have optimum alignment without a technician-constructed alignment jig, connecting the 14-lead jack with enough space to provide access to the two adjustments. This assumes that the extra RF lead lengths would not act as small "antennas," throwing off the whole AM alignment due to stray oscillations. I assume that Sangean has such an alignment setup, so it must be possible to align the radio this way. Unfortunately, with multiple hobby projects having higher priority here (E100 Slider Loopstick article, etc.), I haven't really had time to construct such a DT-400 alignment jig, and ensure its proper function.
Your suggestion of adjusting the 1400 kHz trimmer by a slow incremental method would certainly work well on a radio without such a hair-trigger adjustment tendency, Guy, although the risk of degrading the existing sensitivity due to an inability to "hit the peak" would be too great in the case of the DT-400W, in my opinion. Long term, the only real solution is to tackle the problem head-on, build an alignment jig, and assuming that it is reasonably similar to the equipment that Sangean itself uses, hopefully have a resource where the entire enthusiast group can have optimum DT-400W alignments. The RF design itself has a lot of promise, and with the exception of Richard's unit, quality control does seem to be above average for factory alignments. All three test units here had fine sensitivity, straight from the factory. The price is very reasonable for such a high-sensitivity design, and after using it at Grayland two days ago, it has become my favorite TP-chasing stock Ultralight.
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