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My Cherokee NIGHTRIDER 100
NPC-RC Conversion
by
Billy D. Ward (AKA The C. B. Doctor)
(HERE IS A GREAT RADIO TO COMPETE HEAVILY WITH THE COBRA 29!)

What Is Wireless Marketing Corp Up To These Days?

The Cherokee NIGHTRIDER's...

are a new series of C. B. Radios from Wireless Marketing Corp.
The Company says that the Northstar "export" radios aare no longer being sold due to pressure from the Federal Communications Commission.
Unlike it's predacessor, the new Cherokee series has passed the FCC's requirements for import into the United States as legitimate C. B. Radios.
Pictured above is the NIGHTRIDER 100 Which is in the price range of the Cobra 29 LTD series and to the right is the NIGHTRIDER 150 which is the same size and price range as the Cobra 148 GTL.
These radios, for the money are "head and shoulders" above the comparable Cobra and Uniden radios and much more can be accomplished with these models than any legitimate cb radio that I have seen.
Not pictured is the Cherokee 2100 Base Station Radio which is supposed to compare in quality to the Galaxy Saturn.

The NIGHTRIDER 100
The Cherokee NIGHTRIDER 100 is an AM only C. B. Radio that from the front view appears to be similar to, and has the same measurements as, a Cobra 29 LTD Classic, and it is a 40 channel radio that operates in a frequency range of 26.965Mhz to 27.405Mhz.

That, however, is where the similarity ends. The NIGHTRIDER 100 features an Electro-Luminescent back light front panel That the company calls "Radiant-View" with "Lite Pipe" technology for complete illumination of the front. It lights up with what I consider a rather pleasant light bluishglow that appears white when turned off and has a dimmer switch on the front panel. It is the easiest radio to use during night driving.

"Clear Drive" circuitry gives you clean and clear transmission and reception and from what I've seen on the bench, it is far superior to Cobra's "Sound Tracker".
The "CLEAR DRIVE" SWITCH has three positions to choose from CDS-CDT-NOR. This switch is used to enable the "Clear Drive" audio compander circuit of the radio to provide clear and low noise communications between similarly equipped units. CDS = "Clear Drive System". Makes full use of the Compander feature. elect this when both the transmitting unit and receiving unit are using Compander. CDT = "Clear Drive Transmit". increases the clarity of your transmission when communicating with others not having a Compander. The receiver Compander in the unit will be disabled in this mode to match the non-compressed received signals. NOR = Normal CB Operation without using the Compander.
One unusual feature for a regular C. B. Radio is a built-in roger-beep.
The biggest advantage that the NR-100 has . . .
is that it will easily accept the Negative Peak Compression (NPC) conversion, Which in my book makes it a strong challanger to the Cobra 29 LTD market!

This conversion features Negative Peak Compression (NPC) for the modulation circuit which allows the positive RF peaks, during modulation, to be driven in a normal manner to the maximum attainable level prior to clipping (As much as 175% modulation of the positive peak) while compressing the negative peaks to a point below the clipping level (approximately 98% modulation). Therefore, distortion and spurious radiation that is normally associated with deactivating the limiter circuitry is cut to a minimum. Also, modification of the final Rf stage which from a modulated amplifier to a linear amplifier circuit removes a major portion of the current draw through the AM regulator transistor, allowing it to run a significant amount cooler than with a peaked stock final circuit.

Looking inside for the first time expecting to find a circuit board similiar to the board used in the Cobra 29 LTD Classic, I was very plesantly surprised to see that it has a new board which is very much like a Northstar board that has been shrunk down to fit a 29 size case. Upon further investigation,I found to my great atisfaction, that when Wireless Marketing Corp designed the new line of Cherokee Radios, they kept the circuit as close as possible to the one that was used in the Northstar Radios making changes only where necessary to pass the FCC's regulations for legitimate cb radios. I noticed that there are a lot more surface mount components, probably due to the crowding of the circuit when the board was shrunk.

The first thing that I noticed that was significantly different about the NR-100 from the Northstars is a heatsink inside the radio on the final RF output transistor which is also a different device. All of the Northstars used 2SC2312's but the NR-100 uses a 2SC1969. If the NR-100 was to pass with the FCC, a 2SC2312 could not be used and they required that the RF final be heatsinked to something that has less ability to to dissipate heat than the chassis. So, they overcame that obstacle by simply mounted an wedge shaped aluminum heatsink behind the final to the inside, back of the chassis which requires leaning the final forward at an angle.

Then looking in the area of the AM regulator, I noticed that the driver for the 2SB754 had been changed from a fairly large device, a 2SA1869, to a much smaller TO-92 device, a 2SA1282. The 2SB754 AM regulator is used to modulate the final and the driver instead of using a more conventional modulation transformer.

The modulation circuit is similar to a "current pass" circuit used in a regulated power supply where the current is passed through the regulator ("pass") transistor providing the regulated power supply output voltage. The output of the power supply is continually monitored and a "sample" of the output voltage is fed back to the the circuitry that controls the voltage on the base of the regulator transistor, which keeps the output power within a very close tolerence of the desired value.

In the AM Regulation/Modulation circuit, There are two voltages present at the base of TR-49, the audio from the microphone preamplifier circuitry, and the DC bias voltage which is adjusted by VR-13 to set the operating point of the AM driver, TR-50 and the AM regulator, TR-51. These two transistors, in turn, supply both the regulated DC voltage and high-level modulation for the RF power transistors TR-43 & 44. The range allowed by VR-13 is fixed by R-237, a 3k ohm resistor, which is connected to the DC supply voltage. This value for R-237 severly limits the range of VR-13. The Northstar radios used a 100 ohm resistor which allowed a considerably larger range for the RF carrier output.

The AM/Regulator TR-51 acts like a variable resistor placed in line with the DC voltage to the RF final and driver. When audio coming from the microphone circuit is applyed to the base of TR-49, through R-236 in series with C-187, it is like having the knob of this variable resistor turned back and forth from the center voltage setting at an audio rate. If the audio driver, TR-50 does not supply enough peak audio output to TR-51, the amount of the voltage variation is insufficient to allow the RF output to be modulated to above the limit that the FCC has set for the C. B. Radio service.

In the Northstar radios, L-36, the collector choke for the RF driver was simply a solid wire going thru a ferrite bead. In the NR-100 this is replaced by a 2 watt resistor with a ferrite bead slipped over one end. This was required by the FCC so that the voltage to the RF driver would be limited from supplying it's full capability to TR-43, again so that the power would not reach above the FCC limit.

So with all of these changes the FCC approved the Cherokee radios for importing into the U. S. as regular cb radios but the radio in this condition will not put out enough power to get excited about.

Looking at the PLL circuitry tends to make me think that someone does not want it to be tampered with as it looks like a block of epoxy with a plug on it. I have not attempted to do anything about adding channels to the NR-100 and I don't think that it can be done very easily. However, there is already a rumer that there is a kit that will work to give it the same channels as the "export" radios.
Lets get started with the actual conversion . . . . .

STEP ONE Remove the heatsink that is on the RF final by unsoldering the final along with the heat sensing diodes wires (D88) which is held against the final within the white nylon shourd over the final. Take out the two screws that hold the heat sink to the chassis.

Then using the original screw and white plastic nylon washer mount the final to the chassis using the hole provided for it. Be sure and use the thin mica insulator and lots of White Silicon Paste.

You can make the decision as to whether you mount the temp sensing diode with the white nylon transistor cover or do what I did since it is kind of tricky getting it together whenyou can hardly see it, and simply epoxy it to the RF final.

This step allows the heat generated by the final to sink efficiently into the chassis.

STEP TWO Remove L-36 which is a 2 watt resistor with a ferrite bead on one lead setting near VR-20. Simply place a plain wire through the ferrite bead and bend it into a hair-pin shape and solder it back where you removed L-36.

This step in the conversion will allow the RF driver TR-44 to receive the full modulated voltage from the AM Regulator/Modulator transistor TR-51 so that it can supply the necessary drive for The RF final amplifier, TR-43.

STEP THREE While you are in this area of the board, you will see that there are two wires at TP-7 that are in the same hole. unsolder and pull these two wire ends from the hole. Solder these two ends together making sure that they do not touch anything and take special precaution to see that there is no wire or solder still sticking down though the hole.

Run at least #14 insulated stranded wire from the TP-7 solder pad on the bottom to the Emitter of the AM regulator transistor, TR-51. As a matter of caution, be certain to note that there are two holes at TP-7 Use the one closest to the back of the radio.

This step removes the majority of the problem with TR-51 running overly hot. Even with a stock circuit that has been tuned for maximum power, The AM regulator runs hotter than it should. The DC supply voltage, along with the modulating audio for the RF stage TR-43 & 44 is delivered through TR-51. With this modification, L-34, the collector choke for TR-43 is disconnected from the output of TR-51 and connected directly to the main DC supply voltage, which eliminates over almost 2/3 of the current through TR-51. This causes TR-43 to now operate as a linear amplifier.

STEP FOUR
Remove TR-50 and replace it with a 2SA1869 with the flat side of the device towards the inside of the radio. This Step is necessary because the stock transistor does not drive the AM regulator TR-51 with enough voltage swing to modulate the Rf stage to the maximum peak power output.

STEP FIVE
Remove C-189 and lay it aside for use later on. Prepare a 1N4001 diode (the same kind that is used for the reverse polarity protection diode in almost every radio in existance)by clipping the cathode to 1/8th inch long. Prepare a 100 ohm 1/4 watt resistor in the same manner. Solder the to short ends together.
Now bend the long wire on the diode with a sharp radius back toward the solder joint. If you have done this correctly, the resistor/diode pair should look like the picture to the left.
Now install this assembly in the holes vacated by C-189 with the cathode of the 1N4001 diode toward the back of the radio. Of course this means that the long wire of the diode is in the front hole and the 100 ohm resistor is in the back hole.
Finish by soldering C-189 on the bottom of the board to the same two pads that you just soldered the diode resistor assembly to. This puts C-189 back where it was electronically but it is easier to lay flat on the bottom of the board that the diode resistor assembly would be.
This step allows the positive peaks to be accenuated to a degree that is just short of clipping, while compressing the negative peaks to approxinately 98% modulation.

STEP SIX Next, Remove R-237, a 3K ohm resistor and replace it with a 100 ohm 1/2 watt resistor.
This step of the conversion increases the the voltage available at VR-13, the carrier adjustment, allowing it a much larger range.

STEP SEVEN Next, Remove R-249, a 10K ohm resistor.
This step of the conversion disables the modulation limiter allowing the fullest percentage of modulation that the unit is capable of.

This completes the conversion.

As a precaution, turn VR-13 counter-clockwise before keying mic.

Tune and peak RF Procedure to follow:

Disclaimer: I do not disclaim anything. If this radio is your own property, as far as I am concerned, you may do anything you want to with it. It is none of my business!