You are entirely correct again. I am thoroughly muddying the waters here, and I appreciate your patience while I get my bearings straight on the actual mechanical layout of this beast.There are absolutely no side adjustments on the RF casting. The SX-28's "catacombs" (the heavy, multi-compartment aluminum RF chassis) features all of its alignment screws directly on the bottom plate of the casting, accessible by flipping the radio upside down. They are arranged in rows corresponding to the RF, Mixer, and Oscillator stages for each band.Let's strip away the bad geography and look at the physical reality of what you are adjusting on that bottom plate for Band 1.The Actual Band 1 Layout on the Bottom PlateWhen looking at the bottom of the RF sub-chassis casting, the adjustments are laid out in distinct rows. For Band 1, you are dealing with three specific screw adjustments accessible entirely from underneath the radio:
The Antenna/RF Trimmer (In the front-most compartment)
The Mixer Trimmer (In the middle compartment)
The Oscillator Trimmers/Padders (In the rear-most compartment)
Inside that rear oscillator compartment, Band 1 has two adjustments side-by-side or closely grouped:
a small mica or ceramic Trimmer (for the 1400 KHz high end) and an Oscillator Padder screw (for the 600 KHz low end). Why the Sensitivity is Stuck at 35 µV. Given your precise setup with the OWON generator and the attenuator, if you have already walked through these bottom-plate adjustments and the radio still refuses to drop below 35 µV of sensitivity on Band 1, the 7 KHz IF shift has likely broken the tracking beyond what the factory adjustments can physically handle. Here is why:
The Padder Limit: The Band 1 oscillator padder is designed to adjust the oscillator frequency by just a tiny fraction to get the low end of the dial to track perfectly with a 455 KHz IF. Shifting the IF to 462 KHz requires a massive change in the oscillator's frequency at the 600 kHz mark.
The Result: If you try to peak the padder at 600 KHz, you will likely find that the screw either bottoms out completely or backs all the way out before the signal ever truly "peaks." Because it can't reach the true peak, the front-end RF coils remain severely misaligned forming where the radio is actually listening, destroying your sensitivity.
How to Verify the Tracking Block. With your generator set to 600 KHz and the radio dial set to 600 KHz: Turn the bottom-plate Band 1 Oscillator Padder slowly from one mechanical limit to the other.Does the signal strength steadily rise and then drop back down (forming a clear peak)? Or does it just keep getting slightly louder right up until the screw tightens completely or falls out? If it never passes through a clear peak, the adjustments physically cannot compensate for the $462 KHz crystal. Your options are either to keep hunting for the tracking peak by slightly altering your dial alignment points, or to pull that 462 KHz crystal holder apart to clean the quartz slab in an attempt to drop it back down to a true 455 KHz.
Page: /1_need_help/Gemini_10/Gemini_10.shtml
Last modified: Tuesday, 21 Jul 2026