Question about Radio Shack TRC-447 CB Radio

3 Answers

Catching about 3 pounds of noise!

I just got this radio and had it peaked and tuned then took it and had my buddy set up the standing wave, swr, etc... But i'm still catching around 3 pounds of noise with my car on or off. I'm using a brand new wilson 5000 and an old palomar tx-75 also. Can someone please let me know how to get rid of the noise???

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  • dss9529 Nov 05, 2008

    I have traded in for a Cobra 29 stnw which took care of the problem! I went from 3 pounds of constant noise to none on a typical day.

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Use the radio in another vehicle, or better yet on a power supply. This will rule out the car's power as a culprit. AM radios like CB are prone to ambient noise.

Posted on Nov 05, 2008

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You might have some dirty power as well. Even if your car is off, there are still electronics that are on. For instance, my car stereo system does not fully turn off even when the car is off, it still cranks some power to keep things in your memory like the time, channel presets, etc. The vehicle computer also never turns off. These devices could be adding small amounts of "dirty power" to your electrical system. This would add small electrical pulses through your DC power. Pyramid makes a noise canceling device called the NS-10 for like $5 or so. It can hold up to 10 amps of current and is connected in-line between the cb radio and the battery on the positive cable. I put this on mine and car noise is reduced as much as 60% if I had to guess. What it does is reduce or eliminate the pulses in your DC that can cause radio interference before the pulses get to your radio. Hope that helps.

Posted on Jun 30, 2008

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Good Evening,
I would think the noise you are picking up is atmospheric noise ( space noise as some of them call it ) or also known as sun spot noise ( skip ). Since we are in a downward skip pattern with the sun spots the atmosperic niose remains a bit higher than we may like. When the niose comes in, it appears as a static niose, so if this is the niose you are experiancing, I assume this should quiet a bit as time goes along for the next few years. ( until skip conditions start on an upswing again ) This happens in a cycle every 7 to 11 years on a normal basis. One thing you can do is purchase a noise chopper devise. They sell for between 20 and 30 dollars and can be switched to a low chop ( filter ) or a high chop ( filter ). You need to know that if you use one of these devises to illimenate noise, it that you also illimanate signal. ( you receive less ). I hope in some way this answer has helped. If I can be of any more assistance, please feel free to email me at this address or a personal email at wyoed1@aol.com or call my shop at 307-266-4675, Mod- Fri 9AM-3PM.
Thanks
Ed ( Radio Man)
NC Electronics
Mills Wyoming

Posted on Apr 20, 2008

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1 Answer

What are swr's


The SWR meter or VSWR meter measures the standing wave ratio in a transmission line. The meter can be used to indicate the degree of mismatch between a transmission line and its load, or evaluate the effectiveness of impedance matching efforts.

It is a way of tuning the aerial length to be correct to the radio.

SWR meter Wikipedia the free encyclopedia

Apr 03, 2016 | CB Radios

1 Answer

How do you tune cb radio 75wx st


Not sure what you mean by tune.

If you mean peak and tune, where in you increase the internal power output of the radio, then the quick and dirty way of doing it is, turn VR4 all the way to the left and take the tank slug out of L14. HOWEVER, I prefer to use a watt meter on avg power to adjust L14 to peak, and no more as not to over bias the final. But typically nothing will happen if you do. This will give you full modulation, and full carrier.

If by tune you mean, Tuning the SWR. Then that is a whole different topic.

In this case you don't actually tune the radio. You tune the antenna. If the antenna is not the correct length, relative to the wave length, Frequency of transmission..... then you will have a high SWR and this means more of your RF energy is not leaving the antenna, and going back into the radio. This is bad. this kills radios.

So to tune it you must make the antenna the right length. Here is how to check SWR.

Tune the radio to ch 20. Put the rf/SWR/CAL switch to CAL.
Turn the CAL knob all the way to the left.
Key the radio, and turn the CAL knob to the right until the needle of the meter is at the CAL mark, on the top line of the meter indicated by a little upside down triangle. That is the cal mark. The needle should be on it.
Flip the RF/SWR/CAL switch to SWR while holding the key down.

The meter is now showing your SWR. If it is under 2 you are not real good, but not gonna kill the radio. If you are 1.5 or less you are good to go. Ideally you want to be 1.5 or less if you can.

If it is over 2 you should try to get it lower.

here is how to find out if the antenna is too long or too short.

Turn to ch 1, repeat the steps to check SWR. Then do the same thing on ch 40. Compare the reading. If the reading is higher on 1 then on 40 the antenna is too short, and you need to make it longer. If it is higher on 40 then 1, it is too long and you need to make it shorter.

All antennas have a way of adjusting the length.

Hope this helps.

Aug 10, 2012 | CB Radios

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

Swr meter not moving


follow these steps to adjust the
standing wave ratio(SWR).
1. Turn on the CB.
2. Set S/RF/SWR/CAL to CAL.
3. Key the Mic and rotate SWR CAL so the meter points
to CAL.
4. Unkey Mic.
5. Set S/RF/SWR/CAL to SWR.
6. Key Mic again and note the actual measurement on
the SWR scale. Refer to the following table to interpret
the reading.

1:1 - 1.5 Great
1.5 - 2:1 OK
2:1 - 3:1 Not So Good
Higher than 3.1:1 Terrible

Jan 14, 2011 | Cobra 29 LTD CB Radio

2 Answers

Got it peaked and tuned and hooked up a new coax and mirror bracket and my swr is at 4. Before I did all this I had the stock coax and swr was under 2. What do I need to do to get the swr down?


The antenna needs to be tuned. The reason all of a sudden your SWR is a 4 when it used to be a 2 is, after a peak and tune, the radio is putting out more power, there for more RF energy is being reflected back into the radio. That is why the antenna has to be tuned.

It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to CAL. (CAL stand for calibrate.
3. Key the radio. (Important. Do not talk while keying the radio.)
4. turn the CAL knob up until the meter hits the CAL mark.
5. Now while still keying the radio flip the meter switch to SWR.

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.

Nov 17, 2010 | Cobra 29 LTD CB Radio

2 Answers

I don't understand how to adjust the SWR or how the built in meter works for my DX949.


Here is a basic instruction on how to adjust the SWR. When you adjust the SWR, you are not changing anything on the radio. You are actually tuning the antenna for best SWR. The lower the better. SWR stands for "Standing Wave Ratio" Or in layman's terms, SWR is energy that is reflected back into the radio. The higher your SWR reading, the more RF energy that is not leaving the antenna, and getting reflected back into the radio. This can cause damage to the transmit section of the radio. The length of the antenna is what will change this. The length of the antenna must match the length of the radio wave. The following instruction will explain how to take an SWR reading, and how to use that reading to ascertain weather the antenna is too long or too short.

Here is a quick explanation of the meter. There are 3 settings for the meter. SWR, MOD, and PWR. When you are not keying the radio the meter will show you your receive signal. How strong some ones signal is. When you have the switch on MOD and key, when you talk it shows you modulation. How much audio you are putting through the radio. When its on power, and you key the radio, it shows you your dead key wattage.

Tuning your antenna:

It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to SWR
3. Key the radio. (Important. Do not talk while keying the radio.)

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.

Nov 16, 2010 | Galaxy Radios DX-949 40-Channels Base CB...

1 Answer

I have a cobra 150 gtl dx cb radio. my reception and transmition is not at peek performance. can you help me please? i have tried everything i know to do.


If this radio has been peaked and tuned already, and it is not in need of a full alignment, then it's most likely the antenna.

Your antenna is everything. You need a good antenna, and it needs to be tuned to the lowest SWR.



It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to CAL. (CAL stand for calibrate.
3. Key the radio. (Important. Do not talk while keying the radio.)
4. turn the CAL knob up until the meter hits the CAL mark.
5. Now while still keying the radio flip the meter switch to SWR.

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.

Oct 20, 2010 | Cobra 150 GTL DX Base CB Radio

2 Answers

Tunning the antenna on radio shack cb trc-447


After installing the antenna, follow these steps to adjust the
standing wave ratio(SWR).
1. Turn on the CB.
2. Set S/RF/SWR/CAL to CAL.
3. Key the Mic and rotate SWR CAL so the meter points
to CAL.
4. Unkey Mic.
5. Set S/RF/SWR/CAL to SWR.
6. Key Mic again and note the actual measurement on
the SWR scale. Refer to the following table to interpret
the reading.

1:1 - 1.5 Great
1.5 - 2:1 OK
2:1 - 3:1 Not So Good
Higher than 3.1:1 Terrible

The ideal standing wave ratio (SWR) is 1:1, or a meter
reading of 1 on the SWR meter's top scale. A SWR ratio
of 1.5:1 to 2:1 is excellent for most mobile CB antenna
applications.

Check the SWR on Channel 1 and Channel 40
If the SWR is higher on 1, make the antenna longer
If the SWR is higher on 40, make the antenna shorter
Most antenna's are adjustable. Make small adjustments at a time.

Oct 10, 2009 | Radio Shack TRC-447 CB Radio

2 Answers

When i key up the mike the tx/rx light and the ant


your swr setting are off wack fix your swr

Oct 02, 2009 | Cobra 29 LTD CB Radio

2 Answers

I need the manual/s for a Cobra CB radio, 29LTD Classic,ser#105129711,manufactured 5/01. Thanks for any help you might have, This radio has a built in SWR meter and I need to know how to tune it or do I...


1) push the button marked S/RF / SWR / CAL to CAL

2) Hold in the button on the mic

3) Turn the SWR CAL knob until the needle is over set to the far right of the meter

4) flick the switch (in step 1) to SWR

Your SWR reading will be displayed. The more to the left the better..

Jun 22, 2009 | CB Radios

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