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R7000.22
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1992-09-15
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R7000.22
Part 2/2
Changes for BS-8 Module
I haven't tried the BS-8 module, but encourage you to
try using it as is, without modification unless neces-
sary.
These steps are needed only if you cannot find settings
of the side mounted aligment controls that get the
display to behave as specified in the owner's manual:
1. Remove C233, the 33 pf disc capacitor, from the
printed circuit board.
2. Replace coil L204, the 4.7 microhenry inductor,
with a 6 or 7 microhenry inductor.
Alignment
Follow the alignment procedure in the SM-220 owner's
manual to adjust the panadaptor. This consists of
adjusting 2 potentiometers and 1 trimmer capacitor
through holes thoughtfully provided in the side of the
cabinet.
The alignment instructions rely on the use of the
internal Marker Generator to generate a signal at the
center of the passband. If you haven't converted the
Marker Generator circuit, you can tune your receiver to
a frequency with a signal present at a known frequency
(like 162.550 MHz - the National Weather Service), and
use that as a frequency standard.
Most of the time spent in aligment will be in alternate
adjustments between the trimmer capacitor and the wide
band sweep potentiometer, which interact with each
other.
Wider Bandwidth
The SCAN WIDTH switch on the stock SM-220 can be set to
display a 40 KHz or a 200 KHz wide picture. I adjusted
my modified SM-220 to display a 100 KHz or a 500 KHz
wide picture. By adjusting the controls on the side of
the SM-220, wider bandwidths are possible, but wider
bandwidths make it more difficult to resolve individual
signals close to each other in frequency. As the
bandwidth gets wider, the horizontal sweep loses
linearity, causing the graticule calibration lines to
be inaccurate.
CONTINUED IN R7000.23