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I have a Radioshack trc-487 cb radio with weather band . I would like to turn up the modulation... Peak and tune... get better reception... anything... I would like to know the internal parts I have to tune and there numbers... The works... I have a 102 whip grounded really good and have low SWR readings now but the radio is crackley.... Id like to tune it up and be able to reach out... AM modulation pots.... coils and which ones to adjust and there numbers on the board internally... schematics on motherboard of cb... I cant find anything online and im having to pay to find out.... because i dont know...

Posted by Randy Smith on


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Mr BrokRench

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Hello Randy, do you have a fiberglass or stainless whip? What is your SWR & power meter readings now? --- The stainless whip may be creating a feedback and picking up static from transformers. Do you have a power microphone? If so you need to use a modulation meter to set it for 100% modulation. It could also be causing the crackling, that or your engine alternator.

A 1:1 SWR implies a perfect match between all elements of the antenna system...this is what you want. If an antenna system is not working well, the power reflected by the antenna will travel back through the transmission line and arrive at the output of the transceiver. From a practical point of view, SWR numbers in the range from 1:1 to 1.5:1 are considered to be very good, meaning that the antenna is radiating most of the power sent to it...

I would not recommend tweaking the boards on the realistic radios. You can however tune your whip. Start by making a base coil with some copper wire, 14 gauge will work. Run one end under the whip mount end and then tightly wrap the wire around the base of the whip. Experiment with 20 - 30 wraps for best performance & SWR.

The Astatic 575M6, or the Sadelta MB-4(hard to find) are very good power microphones that will help with modulation and peak power transmissions. Let me know if you need more help with tuning, if the "crackling" is still there.

Here is a link for your radio, in case you don't have one.

Posted on Nov 16, 2011

  • 2 more comments 
  • Randy Smith Nov 16, 2011

    I have got my readings to a 1.2 swr close to perfect.. like i said i have a 102 wire whip.. my whole think is I want to know how to get full modulation, and adjust the internal pots on this radio.. what i need to do internally... It was a free radio. So if it blows it goes... I Have a General Lee that will eat it alive...

  • Randy Smith Nov 16, 2011

    I have got my readings to a 1.2 swr close to perfect.. like i said i have a 102 wire whip.. my whole think is I want to know how to get full modulation, and adjust the internal pots on this radio.. what i need to do internally... It was a free radio. So if it blows it goes... I Have a General Lee that will eat it alive...

  • Randy Smith Nov 16, 2011

    basically i want to let the radio swing... get more watts... without paying anymore money to someone... what do i need to adjust internally... every other cb has something on it... I cant get **** on here.... couldnt catch a skip on a good day with good numbers on swr....

  • Mr BrokRench
    Mr BrokRench Nov 16, 2011

    Ok...on the board the little white and blue pot by the transformer is your modulations. To super swing that radio, you'll have to pull the inductor that feeds the RF driver. The inductor there looks like a resistor and is green. On top of that you have to leave the inductor in and just pull the voltage side. Install a cap and you have to play with the resistor value...youll probally need about a 220 uf capacitor,and somewhere between a 50-100 ohm resistor.the idea is to locate the 13.8 volt dc feed,to the driver section,disconnect it by either cutting the land pattern on the solder side of the pcb.or either disconnecting the proper resistor,choke,or capacitor,whatever the case maybe.what i gently do is locate the pcb land pattern feeding the driver stage,using a exacto knife,gently cut the land pattern,completely isolating it.then install my 220 uf capacitor,on the componet side of the board,then install my 50-100 ohm resistor across the capacitor,on the solder side of the board.remember the negative side of the capacitor,needs to be towards,the driver....usually a 50 ohm resistor,gives you about 2 watt dead key...

    In order to increase your power by 1 S-Unit, you're talking the production of 6 dB gain. That power is generated by doubling the power twice over, so on AM you're talking 12- 16 watts. The adjustment of any "parts" inside your CB is pointless, you can't tweak them that much.... Get an amplifier if you want to produce serious power with preamp for DB gain...Many of the most popular are the Texas Star, Palomar, Xforce, Davemade, Ameritron, and Fatboy, amplifiers...
    This is what i use & i have it tuned down!

    I hope this information is helpful.



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