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EXPANDER 160 & EXPANDER 240 Application Notes
Many people have asked about which CB radio expander kit is best for their particular application. Let’s try to clear this up.
Generally speaking, any CB radio which can use the EXPANDER 240 can also use the EXPANDER 160, but the reverse is not true. That’s because only the EXPANDER 160 includes the oscillator function, which you’d need for many PLL radios. You’d be paying more for an EXPANDER 160 in those applications where you really only need the EXPANDER 240’s crystal switching. You might also want to remove the EXPANDER 160 some day and re-install it in another rig that does need the oscillator function, giving you more flexibility.
On the other hand, the EXPANDER 240 has 6 rather than 4 crystal positions and could be used in the older 23-channel radios with crystal synthesizers. In those rigs the EXPANDER 240 would add a total of [5 x 4 related channel groups] = 20 extra channels. (The 6th slot must be reserved for an existing radio synthesizer crystal.) Not very cost-effective for crystal CBs though: there’s the kit cost, the cost of 5 crystals, and the cost of paying a tech to build and install it if you can’t do it. PLL rigs are the most practical.
We call these kits “160” and “240” because any PLL CB using a mixing signal can theoretically have 40 channels per mixing crystal:
[4 x 40] = 160 and [6 x 40] = 240, respectively. Few American CBs are broadbanded enough to tune this much range though, with the limit typically 120–130 channels total. For example, the popular MB8719/MB8734 Uniden SSB models will tune a maximum of about 130–140 channels, which means 3 full 40-channel bands, plus a partial band on the 4th mixing crystal. Or two full bands on the two middle crystals and two partial bands on the end crystals, depending on where you set the VCO and mixer tuning stages.
Shown below are many common radios by chassis type and kit to use. If your rig’s not on this list, send us a stamped self-addressed envelope (SASE) or E-Mail message with the exact model number. We’ll tell you what if anything can be done to it.
EXPANDER 160:
1. All 23-channel crystal models. (But you'd get only 12 extra channels, where
the EXPANDER 240 would get you 20 extra channels.) This isn't
very practical because a bunch of special-order crystals will be expensive!
2. Any PLL rig using the 15.360 MHz loop tripler mixing scheme. Chips with this method include the LC7120, SM5107, µPD858 (AM 2-crystal scheme only), µPD861, µPD2810, µPD2812, µPD2814, µPD2816, and µPD2824 (SSB).
3. Any late Cybernet PLL02A AM PLL chassis using the 2-crystal scheme of 10.240 MHz and 10.695 MHz. In this circuit the 10.240 MHz PLL reference signal is doubled to 20.480 MHz, and you would replace that signal.
4. Any other PLL rig using a mixing signal that’s not directly derived from a separate mixing crystal. For example all NDI SSB rigs (SBE Sidebander IV, V, Console V, Console VI, Johnson Viking 4730, Messenger 4730, Pace 1000MC/BC, etc.) use a 10 MHz PLL crystal reference, and part of that oscillator signal is sampled off and doubled to 20 MHz to use for loop mixing. In those rigs you’d inject your own new signals in the 20–21 MHz range using an external oscillator.
EXPANDER 240:
1. All 23-channel crystal models. Again,
not very practical because a bunch of special-order crystals will be expensive!
2. Any early Cybernet PLL02A AM PLL chassis using the 3-crystal scheme of 10.240 MHz, 10.695 MHz, and 11.8066 MHz. Here you’d switch in new crystals to replace the 11.8066 MHz signal, which is being tripled to 35.420 MHz anyway.
3. All Cybernet PLL02A SSB American chassis using the 10.0525 MHz mixing crystal, or all "export" multimode chassis using a bank of mixing crystals in either the 10 MHz or 20 MHz range.
4. All the MB8719/MB8734 PLL SSB chassis. Replace the 11.1125 MHz or 11.325 MHz tripler crystal.
5. All the µPD858 AM 3-crystal models. These use 10.240 MHz, 10.695 MHz, and 36.570 MHz.
6. All the µPD858 SSB and SM5104 SSB models. CAUTION! This chassis uses 3 separate mixing crystals, one each for AM, LSB, and USB. Therefore the kit would only work for one mode. That’s fine for 10-Meter Novice conversions if all you care about is USB, but for full CB expansion you’d need three kits for all-mode coverage. Obviously, not very practical.
7. Realistic TRC448, Wards GEN719A: same situation as #6.
8. All Royce models with the "sardine can" type of sealed PLL unit. These generally use a 36 MHz loop mixing signal and the specific PLL chip doesn’t matter. What does matter is that you’d have to run the EXPANDER 240 switching wires into the sealed unit. These wires would be longer than the normal kit mounting location and could cause oscillator instability.
9. Realistic TRC459, TRC480. (Change the 18 MHz mixing crystal.)
10. Any other PLL circuit using a discrete crystal oscillator for loop mixing. You would switch in new crystals to replace that signal. Usually the mixing crystal is around 36 MHz (or a tripled 12 MHz), although a few odd circuits use other crystal frequencies.
For more specific synthesizer details, you might want to order and study the CB TUNE-UP and MODIFICATION REPORTS for your particular radio before proceeding. These include details on suggested new mixing crystals, Clarifier strapovers, peaking, etc.