You need to adjust the front end tracking....................you don't need
to touch the oscillator adjustments that affect dial calibration, but you do
need to adjust the mixer and antenna trimmers and coils. The trimmer caps
are typically adjusted at 1400kHz, and the inductors are adjusted at 600kHz.
The antenna adjustment at 600kHz is made by sliding the coil assembly over
the ferrite core, until a peak response is obtained. Same thing for the
mixer transformer. I am assuming that a 3-gang tuning capacitor is used in
this unit. Finally, you need to go back and forth, at each of these tuning
points on the band, until no improvement, and no interaction is noted. Some
radios have one of the plates of the tuning capacitor slotted on each of the
gangs; this allows you to do 3-point tracking, by bending these sets of
plates at 1000kHz, for best response. Be careful on this adjustment, and
also, redo the adjustments at the other two frequencies afterwards.
> Hi! I have the Radio Shack 12-903 High-Performance radio. I brought it
> and it seemed fairly close in performance to my old Superadio III that I
> years ago, at least for weak night-time signals. The dial accuracy is
> and sensitivity is extremely good up to 1530 kHz. However, "sensitivity"
> declines in a big way beyond 1530 kHz. I put "sensitivity" in quotes
> can still get the signals beyond 1530 kHz--they're not buried in
> have to crank the radio waaaaaaaaaaay up to hear them.
> My questions are these: Is there a good way to correct the sensitivity
> without ruining the dial calibration? Or should I just return it and get
> Grundig S-350 from another store? The S-350 is closer to my needs,
> but the Passport review makes me think that AM is not quite on par with my
> '7600GR or my Satellit 700, and the tuning drift will***me off. I
> always get another SRIII, but that takes away the fun of learning a new