How do i turn the watts down on my CB for an amp

So i recently bought a Kl 203p amp for my cb and need to turn the watts down on my cb to 1.5-2 watts. How would i do that?

 

Take it to a good shop, have it properly aligned and have them turn down the driver in the rf strip.

 

It's cheaper to make improvements to the antenna system. More bang for the buck.

 

I prefer to leave the radio undefiled stock (except to check its alignment and see that it meets spec especially the receiver) and install an attenuator of the proper impedance in the amplifier circuit's input. Match the amp to the radio. I don't use an amp any more.

I agree with the antenna comments. Ihe antenna is the place where more performance gains can be made for the least money and interestingly it is usually the crappiest or most ill-begotten part of most installations. As the speaker system is to the home stereo, the antenna system is to the communications radio. It's always the interface between two media that matters.

 

Payne, I use a quick-and-dirty way of reducing radio output into my amp which is probably condemned by the aristocracy of CB but it works for me.

I use a resistor device on the radio's incoming 12VDC feed to reduce the voltage to an actual ~12VDC instead of the vehicle's normal ~14VDC, or whatever it happens to be.

In my case, I have installed 32 feet (actually 64' +/- combo) of 22 gauge copper wire in the 12VDC feed line to the radio. Via calculations and actual multimeter testing, this supplies about 1.06 ohms to the feed line, which reduces the feed voltage to my 1.7 amp radio to a nominal ~12VDC, which of course varies a bit depending on the actual system voltage of the vehicle at any given time.

Via this crude-but-it-works method, I've measured the radio's actual output to the amp at about two watts, compared to the nominal four allowed by law.

With this configuration, my little KL203P is outputting about 40 watts on trucker's 19, which for me is a sweet spot. It is easy on the amp and keeps it cool, and is great for on-road communications.

In answer to the question, why not just buy a resistor? The answer is, cause I had the wire and didn't have the resistor.

The 32' of two-way copper wire is light and easy to coil up and zip-tie in place. Of course, it is properly protected with a properly sized fuse.

I'm not recommending anybody try this themselves, I'm just responding to the posed question. This is "my" solution to keeping an amp happy without taking the case off the radio and fiddling with the insides. I'm sure it is not approved by the techs; at least, I have not read of anybody else using this "external" approach to amp nirvana. But it made me happy.

 

I agree with it as long as there's enough voltage to run the circuits in the radio without distortion. Most radios run everything off the 12V, except for some 8 Volt and lower regulators inside. Those should be OK with 10V coming in, but who can say what every radio is built like. Most of them used to give a spec, like 10.5 to 13.8VDC but that's so dumbed down these days even the Cobra 29 says '13.8V nom.'
Why every-ting so stoopid now!!

That approach mentioned above has also been used to limit the current taken from the alternator by a large amp. Most people don't know about it and a whole lot of the 'golden screwdrivers' installing stuff at truck stops don't understand how simple it is.

A secondary battery is placed close to the amp and connected directly to it by a short length of the correct large-sized wire on + and - so that the amp can consume its rated current from that battery. An AGM battery won't spill.

A smaller wire is run from that battery's + to the alternator, and its resistance (size and length) is selected so that the voltage drop, from the alternator to the + terminal of the secondary battery, at the desired limited current, gives the same voltage as the seondary battery by itself (fully charged) does under the load of the driven amplifier. The (-) wire from the negative side of the secondary battery and the (-) side of the main battery can be connected using the normal size large wire. When the amp is keyed, 30A will be supplied by the truck and the rest by the secondary battery.

An example if this would be where one only wants to take 30A from the alternator, but the amp wants 100A when driven to full power. The secondary battery can be an AGM battery, about 100AH capacity. Fully charged, the 100A load is checked and it pulls the battery to about 12.4V. The alternator is checked with normal truck loads and found to make 14.3V. The voltage drop wanted (same calculation as the CB radio post above) is 14.3 - 12.4 = 1.9V. The equivalent resistance is 1.9 / 30 = 0.0633 Ohms. Because a big (-) cable is run to the vehicle alternator GND or (-) end of the vehicle battery that small voltage drop (0.1 to 0.3V) can be ignored, but it should still be checked to make sure the connection is good. Using the wire tables, the length and gauge of the + wire from the secondfary battery and the alternator + terminal can be chosen. Fat wires will be longer, thin wires of course shorter. Pick the length slightly over and coil up the remainder and secure it. Fussy folks can trim the length. Remember the goal is to avoid overloading the alternator while keeping the secondary battery charged when the amp is not keyed. A 25FT wire for this could be #14 which is 0.002575 Ohms fer FT. (1.9V / 0.06435 Ohms = 29.5A)

The wattage dissipated in the length of wire would be 1.9V * 30A = 57W so take care to use a large enough wire so that it will not get over its temperature rating as it heats up during the talking. This can vary depending on whether the user is long winded or brief. "normal" users run about 10% talk 90% listen. Jammers will have higher duty cycles up to 100%. The wattage requirement can be multiplied by the duty cycle. Up to 5W per foot of high temperature wire is safe. The same result can be had with a resistor if full size wire is used for the (+) run and drops as little voltage as possible.

In this case the wire is a better solution because an 0.063 Ohm 50W resistor (always oversize) may be hard to come by and the resistance of the various connections could be significant - depends who does it and how. BTW all crimped-on lugs and connectors must be soldered where they are crimpined to the wire because any dirt over time will mess this up.

 

The best solution would be to use a variable attenuator at the output of the radio.

 

that's all good and well but unless it is a switched attenuators, your receive is also attenuated.

But there is hope, most won't do what also works.


Simply put inline with the driver's power, before the choke a resistor to drop the voltage to the driver and it will also drop the watage without effecting the quality of the signal. You can even have it switched so without the amp it is barefoot, switch it on and the voltage drops the power and the amp works well.

 

I have one word that will help alot of use to deal.with all the above info...

WHAT EFFING HELL DOES ALL THAT SUPER TECH TALK MEAN!!

Thank you for yout time,continie with your regularly scheduled reading..

 

Mark speak, a language to confuse and at the same time impress the common man,