Cobra's 29 NW Classic Mobile CB

Cobra's latest 29 radio has all but one of the features of the original Cobra 29 LTD. The missing control is the Delta Tune knob. This was a functional feature back in the 23 channel crystal controlled radio days. The older radios didn't meet the tighter frequency tolerances required of today's CB radios. They also drifted more over time as they aged. The Delta Tune allowed receiver tuning of off frequency transmissions. The PLL radios of today don't drift like the older units, therefore the Delta Tune is useless, except for it's replacement with an echo board dual gang control. The Cobra 29 NW Classic does however have some features that the old Classic didn't have. First is the front mounted mic connector, the channel 9 & 19 switch, and the Night Watch Electro-Luminescent illumination system with dimmer. By the way, if the dimmer control is removed from the front panel, turned up all the way, mounted and insulated in a secure location inside the radio chassis, it's former location can be used for the Connex or Turbo echo control. The Cobra 29 has been the top of the line Cobra AM CB mobile for many years. This radio delivers more modulation swing than the Cobra 148 GTL. Many operator thought they were able to get more power from the 148 because it cost more money and had sideband. On the contrary, because the 148 has sideband, a compromise was made. The audio transformer that delivers the higher voltage to the final and driver stage of the 29 isn't used in the 148. I've seen 20 to 23 Watts peak out of a Cobra 29, were the 148 is capable of 16 to 18 Watts peak. There have been rare cases of a couple Watts more out of these radios, but this is in 1 out of 200 radios. The Cobra 29 is capable of delivering 28 to 30 Watts of peak and 8 Watts of carrier power by changing the final transistor to a 2SC1969 and adding some capacitance and tuning. One area that the 148 GTL excels over the 29 is in the receiver. The selectivity and noise reduction is better in the 148. But they are both very good receivers. There are tricks to lower the carrier of the Cobra 29 transmitter while keeping the modulation swing almost to maximum. Say you have a amplifier that requires 25 Watts peak input to deliver full peak output power, but you only want a 2 Watt dead carrier. First the final output transistor must be changed to the 2SC1969. Then the JP-36 jumper is removed. Add a 50 to 200 Ohm resistor and a 220 MFD 16 volt capacitor in the JP-36 location. See the schematic below for the resistor and capacitor location. Click On Schematic For PC Board Photo The resistance value will have to be selected for the desired carrier level. The lower the resistance, the higher the carrier. For a cleaner signal, don't eliminate the AMC, just adjust it for maximum modulation. Also retune L14 for maximum RF swing then check your carrier level again. It may be necessary to select another resistor value once L14 is readjusted, or a compromise may be achieved to get the proper carrier to swing level desired.

Variable Resistor Trim Potentiometers & AMC Diode

VR1 VR2 VR3 VR4 VR5 VR6 D11

Receiver IF Gain "S" Meter Squelch Range AMC Automatic Modulation Control RF Meter SWR Warning Indicator Cut To Eliminate AMC

Cutting the AMC diode will create over-modulation and distortion

The cosmetics have changed. The front panel is no longer a brushed aluminum panel. It is a simulated brushed aluminum panel with electro-luminescent technology that illuminates the lettering for night vision. It works quite well without being too bright. It gives off a glow similar to an automobile illuminated dashboard. The front mounted mic connector is becoming more of a necessity these days with less room in vehicles including the big rigs. There isn't room for side mount mic connectors in more and more vehicles as the new models come out every year. Cobra has dropped the SoundTracker in the NightWatch versions, but it's still available in the non- illuminated versions. There is a mixed reaction to the SoundTracker system. Many operators don't care for the un-natural sound and slight distortion when the ST is engaged. Many don't understand that for the maximum effect the RF gain control must be set for optimum performance. And other's just can't be bothered to set and reset the RF gain control while they're driving. Manufacturers need to incorporate an inexpensive but effective digital signal processing (DSP) system in their radio. To date this is the best way

to eliminate the most noise from signals before the hit the speaker. And this will be the only acceptable type of noise reduction by the buying public. Gimmicks won't work. The Cobra 29 NW Classic In Daylight Environment

The Cobra 29 NW Classic In Night Environment

If AM is your mode of operation and Cobra is your favorite brand, the 29NW Classic may be the radio you've been waiting for. There are frequency expansion kits available to increase the frequency coverage to 120 channels. This would give the radio 40 channels above 40 and 40 channels below 1. These kits run from $14.95 to $24.95. Keep in mind, the modification of these radios may be illegal in your country. Please check your regulations before attempting to make any modifications on your equipment. Bob F

December 2001 Web Edition