Question about Cobra 29 LTD CB Radio

2 Answers

School project how deos a cb work im doing a school project on radio waves

Posted by on


2 Answers

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 5 achievements.


    An expert whose answer got voted for 20 times.


    An expert who has written 20 answers of more than 400 characters.

  • Expert
  • 66 Answers

When you talk into the microphone your voice which is sound pressure is converted to electrical voltages then it is increased in power to about half of the power of what the CB will sen out to the antenna. To make the CB radio transmit, there is a circuit that creates the proper frequency or channel. It is then increased to about twice the power of the voice circuit. They are combined together just before it goes into the antenna.It leaves the radio and goes into the antenna where it leaves the antenna as an electromagnetic wave. Electricity in the air with a certain value of frequency and strength. When the CB receives, The antenna picks up a signal, an electromagnetic wave, as it passes by. The electromagnetic wave, which is a small voltage, with a certain frequency and strength, enters the radio where it is processed . It is then increased in power . It is now connected to a speaker. The speaker is also a converter. It converts electrical voltage back to sound pressure so we can hear it. As the electrical voltages make the cone of the speaker move in and out. There is a lot more detail than this but this should help. Many things happen inside the radio that cant be explained in a few paragraphs.

Posted on Dec 13, 2011

  • 1 more comment 
  • Iron
    Iron Dec 13, 2011

    No mention of crystals, filters. IC chips or anything. Typical espert.

  • Ernest Taylor Dec 14, 2011

    Ok you want crystals? here it is! In the early days of CB they used crystals. One for transmit and one for receive. that is what it took just to have one channel. Then as time progressed they moved up to 23 channel CB radios. Still using crystals but in a different fashion. They had what was called an oscillator. matter of fact they had two of them just to create the frequency needed for each channel. When transmitting, the two oscillators, each running at their own frequency set by the crystals, would be mixed together in what is called a mixer. The result would be the difference between the two. For example only, say one was running at 20MHz at the other at 7.125 MHZ. The result coming out of the mixer would be 27.125. a CB frequency. You could hack the radio and get another channel other than CB frequencies by changing a crystal, so that when the two mixed together would be the new frequency. I am sure that is why the question must have been asked,where are the crystals. After the mixer the next couple of stages would be radio frequency amplifier stages until the last stage the output stage where it went to the antenna. The output stage had a couple of coils and capacitors which would need to tuned for the center of the band you were using. In this case for about channel 12. You could tweak on these to get a bit more power and improve antenna matching and audio performance. Most CB radios had an automatic gain control pot at the final stage area. It would send a portion of the signal back to the input to cut the power down. By tweaking on that control you could bypass that function. Now when it came to receiving the signal came in through the antenna to the radio where it was first amplified and some even had an "RF Gain" control which at this point is what it operated, the gain of this stage. The output of this stage went into,you got it, another mixer. The signal coming in is mixed with an oscillator to get a frequency coming out of the mixer of 10.7 MHz. The 10.7 MHz is then amplified by a couple of amplifying stages called "IF" stages. stands for Intermediate Frequency. Then the output from the IF stage would go into yet another mixer with another oscillator"called a local oscillator, the result coming out of the mixer was 455 KHz another standard frequency radios use for the IF stage. This is also another IF stage. The mixer did what was called a conversion, hence double conversion radio. From the last IF stage it went through a rectification stage to turn the radio signal into audio, from there to an amplifier stage so you can hear it. By the way the squelch was placed in the audio circuit to eliminate background noise. Setting the squelch control knob sets the level that a signal has to be more powerful than before it trips it. It is like a comparator in that when the voltage level reaches the trip point it turns on the audio stage so you can hear it.
    Now when the new 40 channel radios came out they eliminated most all the crystals.
    They really only needed one crystal for the transmit stage to do all 40 channels. Yeah right you say? The circuit uses a phase lock loop to come up with the right frequency. How it works Is somewhat like this: the crystal is attached to an integrated chip that has a job of dividing the frequency by a certain number. Like say divide by 11,456. Just an example. The end result would be a frequency which was fed back to the input and then it would lock itself on frequency. Its a lot more than that and complicated. Now to get more channels other than 40 channels all you had to do is figure out the combination. You the 40 channel selector knob on your radio is actually selecting different combinations of the chip input leads. By changing those combinations you could go above channel 40 to 41,42,,,,,60 or more. Which of course is illegal. other than that the new ones are equipped with noise blankers to get rid of power line noise and other noises. I think that is enough detail as I am not writing a book. If any of you care to elaborate feel free. Please no more sarcasm. I am only trying to help. not everyone is at the same learning level. It takes time to answer questions in such detail, time I could spend doing other things. I don't mind helping but I am limited to how much time I can spend. By the way you spelled expert wrong, you spelled it "espert".

  •  Laron
    Laron Aug 24, 2012

    ALL HAIL THE MIGHTY IRONFIST109!!!!!!!!!!!!!! I am a fan not to be confused with stalker. His material makes for a informative and accurate on subject read. Can't help but rate his comments as helpful.


  • Level 1:

    An expert who has achieved level 1.


    An expert that got 5 achievements.


    An expert who has written 20 answers of more than 400 characters.


    An expert who has answered 20 questions.

  • Contributor
  • 66 Answers

It is a simple transmission between magnetic wave forms exchanged by two consistent receivers using the sam frequency and modulation. For example, when you key in on a CB microphone, the CB is sending electronic pulses to the mic and when you talk, the waves are sent to the CB and transformed into radio waves by the transmitter and are sent to other components of the CB like if you had an echo board on the CB, if you had the echo activated, the wave would pass through the echo board and would be transformed dramatically depending on how you set the echo, then after the transformation of the waves, they would be sent through your antenna, through the air and then into other people's CB receivers.

Hope this helps!

Posted on Jul 01, 2008


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya Technician can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
click here to Talk to a Technician (only for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Can regent home theater system modle ht-2004 pick up radio signals or cb radio waves.

Most audio equipment will pick up radio waves of various kinds. The question is do you want it to?
If as I suspect you don't then you have a problem. You can get special filters that connect between the aerial plugs and the receiver. These are set up to remove CB radio signals. Your local electrical parts shop or aerial installers will stock them. Also fit cable connections that are good quality, designed with high quality screening built in.

Apr 14, 2015 | home Audio Players & Recorders

1 Answer

Do i need a certain antenna?

The fiberglass provides no ground plane area for the antenna and radio waves. Your Standing waves (aka: SWR or Reflect) are probably very high. I suggest mounting the antenna on the cab of the truck. You "could" try aluminum tape on the cap and mount the sheilded side of the coax to it somehow. Without a ground plane much of the RF Power of you CB will be reflected back to the Final Output Transistor(s) (Final or Finals), overheat it and possibly damage and burn it/them out. If you are just running the CB without an amplifier(Linear or sometimes called a box), a magnetic mount antenna should work fine and be less of a problem than permanently mounted antennas. That's a plus when going into a parking garage. Even if you decice to get an amplifier at a later date, you should be able to use it with the magnetic mount antenna as long as the antenna you but is rated for several hundred watts, you Standing Waves are Low, and the amplifier doesn't put out more power than the antenna is rated for. I hope this helps.

Apr 17, 2014 | Midland 1001Z 40-Channels Base CB Radio

1 Answer

Imtrying to find a good long range long range cb antenna


Feb 18, 2013 | Cobra Hg A1000 Highgear Cb Antenna...

1 Answer

Im having problems with my midland 77-095 im reciving lound and clear but my output is terrible people cant hear me but i can hear them>???? thanks

it is possible you are hearing peoplein skipland. skip is an atmospheric phenomenon that causes radio waves to travel hundreds even thousands of miles. there a lot of cb operators that run high power amplifiers which would make their signal go even further. this would mean you would hear them well, but your radio doesn't have enough power to reach that person. right now we are in a solar cycle which has been causing skip daily. if you know that the peson you are trying to talk to is local and within. a few.miles then there may be an issue wit either your radio or antenna. the antenna must be tunedto the radio or you signal will not radiate off the antenna completely. over time it can destroy the radios transmit circuit. so if you have never.tuned the antenna you may be causing the radio not to work well and you may have hurt the transmit transistor.

Jun 27, 2011 | Radio Communications

2 Answers

Can this SWR be accurately be used for a boat VHF radio antenna? I have tied it and it seem to work but do not know if the reading are good.

Standing wave ratio is standing wave ratio. This meter is not reading based on frequency. It is reading based on the measurement of electrical energy. I see no reason why it wouldn't work.

Jun 22, 2011 | Astatic (PDC7) CB Radio

1 Answer

Won't send out. I have replaced mike already.

if the Mic gain is up. and an antenna is connected. its possible that the transmit circuit is blown out. this is definitely the case if you have been operating the radio and the red ant lift has been lighting when you key up. that means your antenna was not tuned to the radio and your swr was too highroad. swr is standing wave ratio. basically if the antenna is not exactly the right length thenyou create a standing wave that does not leave the antenna and bounces back down the coax into the radio which destroys the transmit circuit. if when you key and there is no signal output then it is shot.

but make sure the cb pa switch is on cb.

Jun 15, 2011 | Cobra 29 LTD CB Radio

1 Answer

Ok so when I bought my '97 jeep wrangler a couple of months ago it came with a CB. It is all hooked up, came with a huge antenna( 4-5ft maybe), all of the lights come on, the weatherman channel works, and...

check the sw's and the antenna. those are SHORT antennas by cb standards. a 1/4 wave is about 9ft long. a full wave is around 36 ft.. so anything shorter than the 102" whips are prone to have less range. if swr check out. the board on the 18's and 19dx styles need to be resoldered from time to time. simple fix .. don't pay more than $8 to fix the radio...

Feb 01, 2011 | Cobra 18 WX ST 40-Channels Base CB Radio

1 Answer

Why dont these reach very far??? i got an Pyramid 20cb antenna Any good??

CB radios are limited to 4 watts input to the 'final'. CB is suppose to be 'line of sight' or about 20 miles. Variables include where you are using the radio ... in the city or in the country ... signal is blocked by buildings and other environmental conditions. A full wave is 36 feet ... is your antenna some number that will multiply to 36 feet? 1/2 wave antenna = 18 feet ... max allowed in the US ... max hight is 20 feet above the mount. If you have an 'old' CB, they were limited to 5 watts to the final. On a good night, one might talk 100 miles away ... but is of course not legal.

Sep 21, 2010 | Uniden PRO510XL 40-Channels Base CB Radio

2 Answers

Radio reception

Cb radio is line of sight. If there is a hill in the way, or some other kind of structure it will block the radio waves.

But also, radio waves, will bounce of the ionosphere and come back down.

So whats probably happening is...

You hear people close because they are near. You can't hear some one some what far away because of hills or something, but you talk to people far away because the are within range of the radio waves bouncing back down to them

Jul 10, 2010 | Cobra 25 WX-NW-ST 40-Channels Base CB...

1 Answer

Cb anttenna

No you cannot, they are on different frequencies. This simply will NOT work. It may receive but will cook the output devices on Transmit die to the SWR being way off.

Mar 13, 2010 | Raytheon VHF 53 CB Radio

Not finding what you are looking for?
Cobra 29 LTD CB Radio Logo

111 people viewed this question

Ask a Question

Usually answered in minutes!

Top Cobra Radio Communications Experts

Level 2 Expert

500 Answers


Level 3 Expert

3289 Answers

Brad Brown

Level 3 Expert

16589 Answers

Are you a Cobra Radio Communication Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides