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R7000.21
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1992-09-15
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R7000.21
In the past month, several Kenwood SM-220 monitor
scope/panadaptors have appeared at hamfests selling in
the $200 to $250 range. The Kenwood SM-220 can display
transmitted or received signals. To add spectral
display capability to the SM-220, one must purchase the
optional BS-5 or BS-8 module, which consist of a prin-
ted circuit board, a steel enclosure, interconnecting
cables, and a new graticule. The panadaptor module
mounts inside the SM-220 cabinet.
The BS-5 is used with the TS520 and TS530 transceivers,
which have an IF of 3.395 MHz. The BS-8 is used with
the TS820 and TS830 transceivers, which have an IF of
8.830 MHz. Since the IF of the ICOM R7000 is 10.7 MHz,
one must alter the panadaptor circuitry to accept 10.7
MHz input.
If you have any choice in the matter, get the BS-8, as
it requires fewer changes than the BS-5, and may even
require no changes at all!
The panadaptor module circuit consists of several
stages, but only two are directly related to the IF
frequency:
1. A crystal oscillator is used as a marker genera-
tor.
2. A voltage tuned oscillator is swept across the IF
of the receiver, and employs a varicap diode, an
inductor and capacitors.
The marker generator is not vital for panadaptor opera-
tion. It merely provides a single "pip" that one may
use to center the display on the CRT screen, and is
similar in purpose to the crystal calibrator in older
receivers.
The marker generator circuits in the BS-5 and BS-8 are
identical except for one crystal. One need only
replace the 3.395 MHz crystal (in the BS-5), or 8.830
MHz crystal (in the BS-8) with a 10.7 MHz crystal to
adapt the SM-220 marker to 10.7 MHz IF. I did not
alter this stage, although I would if I had a 10.7 MHz
crystal handy.
The voltage tuned oscillator is the stage that deserves
our attention. The changes required depend on whether
you have the BS-5 or BS-8 panadaptor module.
Changes for BS-5 Module
Change the following capacitors:
1. C231 from 1000 pf to 68 pf.
2. C232 from .01 uf to 1000 pf. (You can use the
capacitor which used to be C231.)
3. C234 from 100 pf to 22 pf.
4. C236 from 47 pf to 22 pf.
5. C237 from 680 pf to 100 pf. (You can use the
capacitor which used to be C234.)
Solder a 10 microhenry inductor in parallel with L204,
a 20 microhenry inductor.