On 3/19/2010 9:30 AM, Hank wrote:
I have observed (while monitoring mixer output with an oscilloscope
during rf alignment) that the output of the mixer is, at zero beat,
about one half of what it is a few KC away from zero beat on all
bands. I have successfully performed IF and BFO alignment several
times (with the same result each time) and the natural crystal
frequency is 455.9 KC. snip

Hi, Hank

I don't have an SX-28, but have done a similar alignment
with an HRO-50. One key thing is to find the "natural crystal
frequency" with the phasing capacitor set to half mesh.
You need to eyeball that capacitor, in case someone slipped
the phasing capacitor knob zero setting over the years.
If necessary, mechanically adjust the phasing control knob
to zero with phasing capacitor at half-mesh.
Then align the BFO coil for the same frequency, with the BFO
capacitor set to half mesh. If necessary,
mechanically adjust the BFO knob
so the BFO knob reads zero with that half-mesh
BFO capacitor setting.

Then use that frequency to align the IF transformers.
On my HRO-50, I wound up with a 457 KHz IF
center frequency.

73,
Ed Knobloch