CRYSTAL ORDERING
The following specifications should be observed when
ordering crystals.
FREQUENCY: As desired.
ACCURACY: .005% or better.
HOLDER TYPE: HC18/U or HC49/U with solder
leads.
CRYSTAL CUT: Fundamental up to about
20 MHz. Crystals which are
being multiplied in the radio
should be specified as such. (For
example, the 11.325 MHz
crystal used in the
Cobra 148/2000GTL chassis is a
tripler cut type.)
LOAD CAPACITANCE: 10 pF (series) preferred for easy
adjustment. The 32 pF used in
many CB oscillators can be hard
to net by the trimmer alone.
If you already have crystals with different specs, they can be
tried first and will usually work. If you have the plug-in
HC25/U types, these can also be used by drilling out the PC
board holes to fit their thicker pins. The PC foil pads have
purposely been made extra large for this reason. The drill
size would be 0.052." Solder the pins directly to the PCB;
using a crystal socket adds extra shunt capacitance.
HOW TO FIGURE YOUR
NEW CRYSTAL FREQUENCIES
The effect of the EXPANDER 240 in a PLL circuit is always
the same: the new injection signals simply drive the VCO up
or down as required, until the input to the PLL’s
Programmable Divider is correct and the loop locks. (This
assumes the radio has not been modified by binary code
changes, or has otherwise been returned to its stock circuit
configuration before installation.) Figuring new crystal
frequencies is therefore a matter of adding or subtracting the
desired amount of up or down shift, respectively, to the
output side of the PLL’s Mixer stage.
The 40-channel CB band has a total bandspread of 440 KHz
(27.405 MHz - 26.965 MHz = 440 KHz); the older
23-channel PLL radios have a bandspread of 290 KHz
(27.255 MHz - 26.965 MHz = 290 KHz.) For continuous
expanded range, each new crystal must add or subtract
450 KHz or 300 KHz respectively, to the preceding crystal.
When the oscillator signal is used directly without
multiplication, add or subtract the 450/300 KHz directly to
each succeeding crystal. If the crystal is one that’s being
doubled or tripled, add 1/2 or 1/3 of the 450/300 KHz
respectively, to each succeeding crystal.
The same principle applies to 10-Meter Amateur
conversions. If you want the Channel 1 operating frequency
to start, say, exactly 2 MHz higher (28.965 MHz), just add
2 MHz to a direct loop crystal, 1/3 of 2 MHz (667 KHz) to a
tripler crystal, or 1/2 of 2 MHz (1 MHz) to a doubler crystal.
Refer to the later examples, which should clarify this idea.
CRYSTAL SUPPLIERS
CRYSTEK CORP.
2351/2371 Crystal Dr.
Ft. Myers FL 33907
TEL: (800) 237-3061, (941) 936-2109
FAX: (941) 939-4226
www.crystek.com
INTERNATIONAL CRYSTAL MFG.
10 N. Lee Av., P.O. Box 26330
Oklahoma City OK 73102
TEL: (800) 426-9825, (405) 236-3741
FAX: (405) 235-1904
www.icmfg.com
JAN CRYSTALS
2341 Crystal Dr.
Ft. Myers FL 33907
TEL: (800) 526-9825, (941) 936-2397
FAX: (941) 936-3750
PARTS SUPPLIERS
CIRCUIT SPECIALISTS INC.
220 S. Country Club Dr. #2
Mesa AZ 85210
TEL: (800) 528-1417, (480) 464-2485
FAX: (480) 464-5824
www.web-tronics.com
DIGIKEY CORP.
701 Brooks Av. South
P.O. Box 677
Thief River Falls MN 56701.
TEL: (800) 344-4539, (218) 681-6674
FAX: (218) 681-3380
www.digikey.com
MOUSER ELECTRONICS
1000 N. Main St.
Mansfield TX 76063
TEL: (800) 346-6873, (817) 804-3888
www.mouser.com
___________________________________________________________________________________________________
EXPANDER 240 PAGE 3
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