It seems it would be a lot better to just allow continous rotation
so you wouldnt have to go back through all the positions when going
from a high band to a low band.
Yes, on a simpler radio that doesn't have a moving band pilot lamp or shadow
indicator, you certainly could let the bandswitch rotate 360 degrees in
either direction.
This stop is needed because the SX-28 has two string-driven shadow band
indicators, behind the main tuning and bandspread dials, respectively. The
indicators run on little elevators that can go up in one direction, and down
in the other. When an elevator hits the top floor, there's only one
direction to go, and vice versa :-)
The diagram at
http://antiqueradio.org/art/temp/SX28DialStringing.jpg
doesn't show all of the parts and pieces, but it does show the strings,
springs, and major doohickeys that make it work. The crossbar carrying the
main tuner shadow indicator is shown where an arrow points to C. The shadow
indicators are simply bent pieces of flat metal with arrow shapes on the
end, which create shadows by sitting between the pilot lamps and the tuning
dials.
Looking at the diagram, find the main tuner bandshaft, where it says
"connected to main tuning knob." If you turn the main tuning knob
counterclockwise, to move you from a lower band to the next higher band,
that will tighten the two sets of strings and lift the two shadow indicators
upward on their elevators. Turn it clockwise, and it will lower the
elevators one floor. But beyond the top and bottom floor, you can't go any
farther without breaking the strings.
Lest you think this is over-complicated, my Midwest DD-18 (
http://antiqueradio.org/MidwestDD-18.htm ) has gizmos that move a pilot lamp
up and down behind a red/green colored screen to illuminate the chosen bands
on the tuning dial. A "Tunalite" circuit is fed off the AVC line and
darkens/brightens the pilot lamp as you tune into a station. A lamp mask on
the bottom half of the dial changes to illuminate the Wavelength markings
accordingly. The good news is that the whole thing is gear-driven -- no
strings to replace!
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html