Adding extra channels to a Uniden-design SSB CB radio that uses the MB8719 PLL has been done a variety of ways. The most-crude uses three two-position switches to cover down to 26.815 up to 28.045 MHz. Using only two switches, as you would in the newer RCI-made Galaxy 40-channel CB will skip channels between 40 and 45. The third switch serves to fill in that gap.
Some years ago we worked out a way to use two switches on the front of a Uniden-style 148GTL to fill in the blank spot. Still takes two switches to select four combinations. The normal 40, lowers, upper channels between 41 and 72, then the channel 60 to 104 "band".
Our fix for the "third switch" problem uses a NPN transistor to invert the logic level feeding from the channel selector to pin 11 of the 8719.
Bill of materials:
1) 2.2k or so pullup resistor. I don't recommend a value below 1k, or above 4.7k. This is the middle ground between the max and minimum resistance to use. This is digital, so it's not critical.
1) 10k 1/4w resistor. Probably could use any value from 8.2k to 22k, but 10k has always worked for us.
1) PN2222A or 2N222A or 2N3904, 2N4401 or any of hundreds of NPN small-signal transistor types. Gain and frequency response almost don't matter. We're using this part only as a switch, and a very low-current switch at that.
This customer wanted his extra channels on the 'Off-ANL-NB' switch. That leaves us only three, uh "bands", not four. He doesn't care about going above channel 72, so we can get by with a single three-position switch for lowers, normal and uppers to 72.
This trick has been adapted to a rotary switch, but we aren't going there today.
First two details are to:
1) replace the 11.1125 MHz PLL crystal with the 11.325 MHz type used in other Uniden models.
No I don't sell those. You are on your own to cobble together this item.
This one came from a derelict radio, probably a smashed Grant XL.
Second detail is to cut the ground connection from pin 10 of the 8719.
Yes, you have to cut it on both sides of the pad for that pin. Just take care not to cut the thin trace to its immediate right. This will disable all transmit. Never mind how I know. Ignore the orange wire. It's there to "lock" receiver to transmit frequency on the clarifier.
Next, unsolder the tiny wire jumper that spans this diode symbol found between the 8719 and the front edge of the pc board.
The two empty holes in this pic show one trace that leads to pin 11 of the 8719, and the other trace leading to the channel switch wiring.
Next step is to hijack the ANL/NB switch. The noise blanker uses the left side of the switch from this perspective. We'll cut the two traces leading to that side of the switch and solder a glob to connect the foil pads together on the rear side of the cuts. This enables the blanker all the time. Skip this if you don't want that.
The right side of the switch has a brown shielded wire with a red and white conductor inside the shield. Those wires have already been pulled in the pic above. Leave them alone, but insulated. Joining the red to the white will TURN OFF the ANL. Leaving them not connected turns the ANL on. Your choice.
Next we solder two wires to the 8719. I used a white wire for pin 10, and a black wire for pin 11. Yeah, shoulda used black for 10 and brown for 11. Couldn't find the spool of brown wire. Besides colors don't matter so long as the right wire gets attached to the right spot. The 2.2k pullup resistor has one end soldered to the 8 Volt DC trace that powers the 8719 and to the channel-selector trace at the other end. Note the empty hole next to where the resistor is connected to the switch trace. We'll be putting a wire there soon. The other ends of all these wires will be connecting to the hijacked NB/ANL switch.
Maybe I should have just shown this pic alone, with all 4 wires. Turns out I did find some brown wire. It's soldered to a ground foil. The orange wire goes to the empty pad connected to the channel switch wire.
Here's where 3 of the four wires from the 8719 will go. The 10k resistor lead is only wrapped around the switch pin. Soldering it to a short pin with no foil pad is fiddly, but doable.
Here is the final link in the chain, the small-signal NPN transistor. The pinout from left to right is emitter, base and collector.
So this begins to look a bit like a game of "Twister", but I tried to get the perspective of where things go clear enough to use.
I should have tried a better angle for this, but the emitter of the transistor goes to the foil trace with the brown ground wire on it. The collector goes to the top-most pins of the switch, lapping both sides if the switch together. For now, the base lead has been bent upwards for the next step. The orange wire is lapped around the side of the 10k resistor already soldered to the switch.
Lastly, the upturned base lead gets lap-soldered to the free end of the 10k resistor.
This is the last step, except to check the PLL tuning voltage at the lowest and highest channels. Should cover it without bumping its head into the ceiling, so to speak. If it does, a tiny tweak to L13 should restore a full tuning range from top to bottom.
The 142 is fairly broad banded, so touching up receiver and transmitter alignment should not be tricky.
But that's the setup. Flip the switch down for lower channels down to 26.815. Center position for channels 1 to 40, and up for channels above 40.
Forgot to snag a channel list for this one. With any luck I'll remember next time I'm at work.
Have fun and 73.
Some years ago we worked out a way to use two switches on the front of a Uniden-style 148GTL to fill in the blank spot. Still takes two switches to select four combinations. The normal 40, lowers, upper channels between 41 and 72, then the channel 60 to 104 "band".
Our fix for the "third switch" problem uses a NPN transistor to invert the logic level feeding from the channel selector to pin 11 of the 8719.
Bill of materials:
1) 2.2k or so pullup resistor. I don't recommend a value below 1k, or above 4.7k. This is the middle ground between the max and minimum resistance to use. This is digital, so it's not critical.
1) 10k 1/4w resistor. Probably could use any value from 8.2k to 22k, but 10k has always worked for us.
1) PN2222A or 2N222A or 2N3904, 2N4401 or any of hundreds of NPN small-signal transistor types. Gain and frequency response almost don't matter. We're using this part only as a switch, and a very low-current switch at that.
This customer wanted his extra channels on the 'Off-ANL-NB' switch. That leaves us only three, uh "bands", not four. He doesn't care about going above channel 72, so we can get by with a single three-position switch for lowers, normal and uppers to 72.
This trick has been adapted to a rotary switch, but we aren't going there today.
First two details are to:
1) replace the 11.1125 MHz PLL crystal with the 11.325 MHz type used in other Uniden models.
No I don't sell those. You are on your own to cobble together this item.
This one came from a derelict radio, probably a smashed Grant XL.
Second detail is to cut the ground connection from pin 10 of the 8719.
Yes, you have to cut it on both sides of the pad for that pin. Just take care not to cut the thin trace to its immediate right. This will disable all transmit. Never mind how I know. Ignore the orange wire. It's there to "lock" receiver to transmit frequency on the clarifier.
Next, unsolder the tiny wire jumper that spans this diode symbol found between the 8719 and the front edge of the pc board.
The two empty holes in this pic show one trace that leads to pin 11 of the 8719, and the other trace leading to the channel switch wiring.
Next step is to hijack the ANL/NB switch. The noise blanker uses the left side of the switch from this perspective. We'll cut the two traces leading to that side of the switch and solder a glob to connect the foil pads together on the rear side of the cuts. This enables the blanker all the time. Skip this if you don't want that.
The right side of the switch has a brown shielded wire with a red and white conductor inside the shield. Those wires have already been pulled in the pic above. Leave them alone, but insulated. Joining the red to the white will TURN OFF the ANL. Leaving them not connected turns the ANL on. Your choice.
Next we solder two wires to the 8719. I used a white wire for pin 10, and a black wire for pin 11. Yeah, shoulda used black for 10 and brown for 11. Couldn't find the spool of brown wire. Besides colors don't matter so long as the right wire gets attached to the right spot. The 2.2k pullup resistor has one end soldered to the 8 Volt DC trace that powers the 8719 and to the channel-selector trace at the other end. Note the empty hole next to where the resistor is connected to the switch trace. We'll be putting a wire there soon. The other ends of all these wires will be connecting to the hijacked NB/ANL switch.
Maybe I should have just shown this pic alone, with all 4 wires. Turns out I did find some brown wire. It's soldered to a ground foil. The orange wire goes to the empty pad connected to the channel switch wire.
Here's where 3 of the four wires from the 8719 will go. The 10k resistor lead is only wrapped around the switch pin. Soldering it to a short pin with no foil pad is fiddly, but doable.
Here is the final link in the chain, the small-signal NPN transistor. The pinout from left to right is emitter, base and collector.
So this begins to look a bit like a game of "Twister", but I tried to get the perspective of where things go clear enough to use.
I should have tried a better angle for this, but the emitter of the transistor goes to the foil trace with the brown ground wire on it. The collector goes to the top-most pins of the switch, lapping both sides if the switch together. For now, the base lead has been bent upwards for the next step. The orange wire is lapped around the side of the 10k resistor already soldered to the switch.
Lastly, the upturned base lead gets lap-soldered to the free end of the 10k resistor.
This is the last step, except to check the PLL tuning voltage at the lowest and highest channels. Should cover it without bumping its head into the ceiling, so to speak. If it does, a tiny tweak to L13 should restore a full tuning range from top to bottom.
The 142 is fairly broad banded, so touching up receiver and transmitter alignment should not be tricky.
But that's the setup. Flip the switch down for lower channels down to 26.815. Center position for channels 1 to 40, and up for channels above 40.
Forgot to snag a channel list for this one. With any luck I'll remember next time I'm at work.
Have fun and 73.
