Add Channels

This page describes a method of adding more channels to the
Uniden / President Grant (PC-409), Madison (PC-411) and Cobra 148GTL (PC-412)


The radios essentially use the same PCB that is why this mod is almost identical for the sets, there are only a couple of minor differences between the them.

The sets are assumed to be on the FCC band but this mod can be applied to sets with a different country frequency such as NZ etc. The set will just be 64 channels above its normal range.


How about adding another band of channels in just 10 minutes !

This will disable the channel 9 function but im sure that you want care about that !

Just remove D28, D29, D30, then on the Grant remove the yellow wire (the one that goes to the channel display) from the junction of these diodes and ground it !

Then add a jump wire between pin 10 of the PLL and the junction that the display wire was just removed from.

Retune if needed

With the channel 9 button in you will be 64 channels above the normal ones !

Channel 1 will be at 27.605 Mhz thrue to channel 40 at 28.045 Mhz !

But DONT use any frequency over 28.000 Mhz as this is amatuer territory !


Mod. Boosts

This section describes various methods of boosting the modulation level on the Uniden / President Grant and Madison


None of the sets that i have come across have ever had more than 80% mod !


The simplest modification on the Grant is to replace the resistor that is located directly in front of TR 26 with a 270 Ohm resistor this will increase the modulation a good amount, (the resistor is not labeled on the PCB, it has silk screen markings for a diode, this is used in the Madison and goes to a VR) this should give at least 90 % mod.

For both the Grant and the Madison adding resistance to the collector of TR 24 (the middle leg) will give a very good increase, 800 Ohms does a very nice job !

If these modifications dont give enough mod then do this as well, in both the Grant and Madison there is a resistor in series with the audio path, R126 , replacing R126 for a 4.7 K Ohm will boost it up but may increase the chance of RF entering through the mike line, this will only work if one of the previous mods has been done otherwise the set will simply be having to cut off more signal to keep the level down.

Also make sure that the reason for the lack of mod is not that the power output has been turned up too high, these sets are only capable of around 4.5-5 watts with 100% mod,some are not even able to do that ! The best set that i have seen was only able to do 5.5 watts with full mod !

Remember dont get too carried away with getting loud, if you go above 100% mod then you WILL cause splatter and interferance to the people using any channels near the one that you are on, and they will probably get very pissed off with you !

Besides, when a C.B. goes over 100% mod they usually end up distorting and sounding bloody horrible !


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