Specifications

EXAMPLE B: Cobra 134/138/139/Midland 13-895 AM/SSB chassis.
This uses 8 MHz and 11 MHz mixing banks, with a 7.8 MHz
Carrier Oscillator. The 8 MHz are the ones to change, since there are
six of them. Once again, they change in 50 KHz steps: 8.1590,
8.2090, 8.2590, 8.3090, 8.3590, and 8.4090 MHz. The next three
for continuous higher frequencies would be 8.4590, 8.5090, and
8.5590 MHz. This gives you the next twelve channels (Ch.26-37)
from 27.265 MHz to 27.375 MHz in the Ch. 1-4 positions, four
channels for each of the three new crystals plus the original 8.4090
MHz.
For 10-Meter use, add the desired Ch.1 up-shift to the highest radio
crystal, 8.4090 MHz. You’d then install up to ten new 8 MHz
crystals, six in the radio, and four more in the EXPANDER 160.
NOTE: These old CBs will never cover both the 10M and 11M bands
without retuning. You could get a straight 23 channels on
10M by just replacing the existing six crystals, without using
the EXPANDER 160. Using it, you’d get 23 channels plus
12 channels more, for a total of 35 channels on 10M.
This assumes you’re willing to buy a total of ten new crystals,
six to replace the radio’s originals, plus four to fit in the
EXPANDER 160. Obviously, you could choose anything
from 12 channels on up to 35, depending upon how much
you’re willing to spend on new crystals.
TYPE 2 INSTALLATION — All PLL AM or AM/SSB with
Doubler or Tripler Oscillators
Refer again to the sketch above. In these radios, the crystal oscillator
is doubled or tripled in frequency to get close to the output frequency
of the VCO, which is typically operating in the 33-38 MHz range. The
multiplier stage can not be bypassed for two reasons:
1. The SSB versions will have USB/LSB offset tuning
adjustments following the multiplier stage.
2. There is usually a Delta-Tune (AM-only rigs) or Clarifier
(AM/SSB rigs) circuit on the low side of the crystal, which
must be retained for proper operation.
The EXPANDER 160 must be used in its SWITCH Mode for these
types. Jumper for this configuration as previously described. Remove
the radio’s loop mixing crystal, and install it in the EXPANDER 160
along with your new crystals. Remember to use the correct crystal
positions that match your desired switching order. Install two short
hookup wires in the EXPANDER 160’s “A” and “B” holes. Place the
other wire ends in the corresponding high side (“B”) and low side
(“A”) holes where you removed the radio’s crystal. The net effect is
that you now have several loop mixing crystals in series between the
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EXPANDER 160 PAGE 5