Specifications

EXAMPLE A: Cobra 29 AM chassis. This uses the standard
23 MHz and 14 MHz mixers, with the 11.730 MHz RX and
11.275 MHz TX oscillators. There are six 23 MHz crystals,
and these are the ones to change. (TYPE 1-B.) Note that they
change in 50 KHz steps: 23.290, 23.340, 23.390. 23.440,
23.490, 23.540. The next three for continuous lower
frequencies would be 23.240, 23.190, and 23.140 KHz.. This
gives twelve continuous lower channels from 26.955 MHz
downward in the Ch. 1-4 positions, four channels for each of
the three new crystals plus the original 23.290 MHz.
EXAMPLE B: Cobra 134/138/139 and Midland 13-895
AM/SSB Uniden 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 higher
frequencies starting at 27.265 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 up-shift directly to the
highest radio crystal, 8.4090 MHz.
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 even using the
EXPANDER 240. Using it, you’d get 23 channels plus
20 channels more, for a total of 43 channels on
10M. This assumes you’re willing to buy a total of
twelve new crystals, six to replace the radio’s
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EXPANDER 240 PAGE 5