Radioshack trc-487 I need to know what on this cb radio I can tune??? Like for Modulation and power? What coils I tune? Let me know what I can do to beef this one up a little bit... Other than going to a Galaxy with a linear! haha

• There is no need to send the radio to some unsanctioned moonlighter.
• I normally don't recommend clipping parts but for this radio there is not much else to do and it looks OK on an Oscilloscope too. Clip diode 205 to increase modulation. Then take a plastic flat tool and spread L 203 coils apart about a 1/8" each, nice and even and make sure they don't touch any metal.
  

• Hope this helps.
  

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.

http://support.radioshack.com/support_electronics/36554.htm

If you take it to local cb shop. Look in your area, for local cb shops. All you really have to do, if you cant find one in your area advertised. Is go to any local truck stop , the mobile cb guys most time advertise there on there community board.But what I would do, is ask some of the truck drivers there, they will be glad to help you. ( i am x truck driver) they can tell you in your area, where the best cb shop is. They will either take your unit and beef it up, but best way to beef it up, is outside power source. They have all kinds of power amps, that will hook into yours to create more power and boost. and of course your antennas have a lot to do with this. BUT caution, make sure if you don't know how to do it yourself, that you have them set you up and tune it in, otherwise YOU WILL, destroy and burn up your unit. cobra 29 is good radio, however to beef it up, or add external power to it, you need a pro to do it, most cases you can beef it up another 150 watts for about 50 bucks. I hope this helps, thanks mike

hello,
The limiter is what limits the modulation. Often times there is a pot that you can turn to adjust it. To get more power and swing out of your radio do this DM1 is the mod limiter RVM1 is the mod pot. Adjust this for maximum modulation. Spread the coils marked Lt5/LT12 just a little Spread LT7/LT11 a lot.
Regards, Tony

The light you see lighting up dictate how much power you have on transmit (TX) and the strength of your receive (RF) The more lights on transmit the stronger your signal. The more lights lit up on receive dictates how hard they are hitting your radio. Either by power or distance. Is this setup in your car or at you home? Many use a mobile CB in there home off a power supply. Either way I am very concerned about you only getting out a couple blocks. I will help you fix this. First your antenna is a major part of your set up. Spare nothing when buying this. I recommend Wilson 300 or higher for the mobile and IMAX 2000 for home. Some Wilson antennas tune and some don't follow the instructions that come with it and ask me if you are unsure. A good 50ohm coax is necessary too. RG58 or better. For just the CB in the mobile RG58 will do just fine. Now we get to your SWR (Standing Wave Ratio) which deals with return loss and reflection coefficient. To high of an SWR and you will lose a lot of your signal and you can burn up your radio. Your radio does not come with an SWR meter so you will need to purchase an SWR/watt meter and put it inline. The coax from your antenna will run into your meter and then run another coax from your meter to the radio and follow the instructions on how to adjust and check your SWR. So now we are at the point where your set up is properly set up and now to tune that radio up. These radios do not carry much power or have much modulation. The limiter in your CB is what limits the modulation. In your CB there is a pot that will adjust this. Here is what you need to do to get more power and more modulation out of your CB. VR2 is the modulation pot. Adjust this for maximum modulation. Now spread the coils marked LT5/LT12 just a little and spread the coils marked LT7/LT11 a lot. Being a new radio it should not need a receive adjustment at all. Moding the receive includes jumping the PLL and I don't recommend that. You may try to replace that potentiometer but outside of this and the steps above you should have a great CB when completed. Good luck, this should fix your CB set up just fine.

look up the tune mods online for that model i couldnt find them myself but a power mic might be your solution.

We all know one is not "supposed" to up the power on a standard CB to more than 4 puny watts...lol. Get your favorite local technician to do a good combination of power/modulation final tuning. Excellent modulation is what really makes the difference, along with a strong power mike. Cobras are known for good quality modulation! Thanks, Bill

RV2 is modulation. turn that up to get full modulation. L9 and L12 is AM power.

Here is a link to the Phantom CB's seb site, you can click on the brand of radio you want to peak, in you case, Cobra. Then follow through the chart to the Cobra 29 LTD Classic under the Cobra power mods, which tells you what to adjust and changes that can be made. Only one suggestion I have before you start, where it says to cut D11, don't, only turn up VR-4 for your modulation. That is the only thing I don't like with their instuctions is telling people to cut the modulation limiter. You can get full modulation by turning up the potentiometer, and if you cut the limiter, sometimes it will over modulate.

http://www.714xpress.net/714mods1.html


You need an inline power meter to peak the radio out. This is the quick and dirty way to peak and tune a radio. To properly align a radio, you really need an oscilloscope and other related test equipment.


If you have more questions, don't hesitate to post here or email me at [email protected]. I can't promise I will have an answer to all questions, but I will do the best I can to help.


Dean Pitts
Rollin CBs

Hello candy_72_99,

Hello candy_72_99,

If I am correct what you are saying is that your radio has poor modulation? ok. First I need you to run two tests for me.

1) Power output Test: connect a power meter to the antenna jack and the other connector of the meter to the antenna, Key up the mic and record the power reading is should be 4W PEP or 36.02dbm

2) Then I want you to take an oscilloscope and put a 1khz tone in to the mic while measuring the RF output at 100% modulation the wave form should not clip.

If these two test are good then your modulation is ok. What I believe you are asking for is more power or better power efficiency.

Try to tune your antenna for 1:1.0 or 1:1.2 SWR with a SWR meter this should deliver the full power to your antenna.

I hope this helps

Thank you,

Shuttle83