Question about Radio Shack TRC-447 CB Radio

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When mic is keyed, TX light illuminates but power meter does not

Radio turns on, channel selection works but when the mic is keyed the swr/power meter does not move. The transmit light works when mic is keyed. Anyone have suggestions?

Thanks for your help!!

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Make sure your s/rf switch is in the right place on the radio is the most common problem i have found

Posted on Feb 08, 2009

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No instructions were included in package.


swr meter operation as follows go to channel 1 flip the switch on the swr to cal key the mic adjust the needle on the swr meter to the dash mark at the far right of the meter use the dial on the meter to adjust then unkey your mic and flip your switch to swr re key the mic you should not be higher than 1.5 on any channel repeat the proccess on 20 and chan 40 if the swr is higher on 40 than 1 lower the antenna or trim it but only 1/4 inch at a time.

Mar 24, 2011 | Astatic (PDC7) CB Radio

2 Answers

When Mic is keyed TX illuminates but no green nand red bars light up. Anh help appreciated.


Get a SWR-PWR meter to put on the line between the radio and antenna to see what it is doing.

Feb 16, 2011 | Cobra 19 DX IV CB Radio

1 Answer

Every time I press my MIC to speak into it the red lights on the RX/T and ANT light come on alerting me of a problem. How can I fix this.


RX/TX light should change to red, however the ANT light is a bad light. This means that your antenna is not adjusted properly. Do not key the radio or talk on it for any other reason then to check the SWR and tune the antenna. If you have the manual that came with your cobra 29, there is a section that explains how to check the SWR. And the manual for the antenna, it will explain how to adjust it.

If not, here is how to do it.........

How to check the SWR on a Cobra 29

Step 1. Find out what your current SWR is on the center of the band.

  1. Turn the radio to channel 20.
  2. Set the S/RF SWR CAL switch to CAL.
  3. Turn the CAL knob all the way counter clockwise.
  4. Key the radio. Do not talk into the mic.
  5. While holding the mic key, turn the CAL knob to the right until the needle reaches the CAL mark on the top right of the meter.
  6. Now flip the S/RF SWR CAL switch to SWR while still holding the key on the mic.
The needle should fall. Where ever the needle is while holding the key is your SWR reading on channel 20. It should be as low as possible. If its a reading of 2, then its not gonna kill the radio but is border line. Any higher and its bad. Using the radio like this will damage the final output transistor. If its less then 2 this is better. You want it to be less then 1.5 or better.

The ANT light may come on with an SWR of 2. running the radio with an SWR of 2 shouldn't hurt the radio, but I don't like to mess around. Get it as low as possible.

How to adjust the antenna for SWR

The length of your antenna will change your SWR. SWR is basically how much RF energy is not leaving the antenna and getting reflected back into the radio. That's why it hurts the radio when its high. An antenna has to be the right length, matching the length of the radio waves in order for it to radiate all of the RF energy out of the antenna.

Most antennas have a way of lengthening or shortening the antenna. If its a mag mount antenna with a metal whip, there is probably a set screw that when loosened, will allow you to raise or lower the whip. If its a fiberglass antenna, under the rubber cap at the top is how you raise or lower the antenna.

Figuring out if your antenna is too long, or too short

Here is how to know weather or not you have to lengthen or shorten your antenna.

  1. Take an SWR reading as explained in the first step on channel 1. Write down the SWR for reference.
  2. Take another SWR reading on channel 40. Again write it down for reference.
Now if the SWR is higher on channel 1 then on channel 40, its too short. You need to make it longer.

If the SWR is higher on channel 40 then channel 1, then the antenna is too long. You need to shorten it.


Make small adjust ments about an 1/8th to a 1/4th inch at a time. each time checking the difference between channel 1 and 40.

You will know when you are a good match when there is little to no difference between channel 1 and 40's SWR. Once you are satisfied that the difference between 1 and 40 is about the same, and much lower, then turn the radio back to channel 20 and take an SWR reading.

You will now find that the SWR on channel 20 is really low. Most likely under 1.5 or better, Almost nothing on the meter.


Here is a Meter Key, so you know what you are looking at.
2d03348.jpg

Oct 11, 2010 | Cobra 29 LTD CB Radio

2 Answers

Cobra 18 wx st receives-wont transmit


Take the cover off, flip it over solder side up, check all solder joints for cracks, cold solder joints, check the safety diode where it comes in the radio, before I go further, can you pick up the weather channel?...Does the PA work?...need to check the pre-driver and finals,audio chip, hook up the power meter using a coax three foot jumper from the output from radio to the input of the watt meter, then the antenna, first check the SWR, on the scale on the meter to cal/swr mode,adjust it to spec, then while still keyed down turn the dial to SWR,if it is the safe range your ok,then turn the Dial to 10 or 20 watt scale and key the mic. Does it have any wattage? If not suspect the finals, they are located on the back rail, if it does have RF then its the audio chip, its located on the right side rail facing you,closest to you.remove it and replace it with same ....hope this helps....

May 21, 2010 | Cobra 18 WX ST 40-Channels Base CB Radio

1 Answer

29 LTD CB Radio: Calibrate cb radio...


The CAL is to calibrate meter for reading SWR (standing wave ratio) which is reflected power when transmitting back to receiver(radio) from antenna system.
This CAL switch position when selected and mic keyed uses the CAL knob to align the meter needle with inverted red triangle next to cal on meter. Then when you select SWR switch position meter will display accurately when mic is keyed for that channel. Now notice the difference when you go between channels 1 and 40. The ant led light will act as idiot light if it is not lit then you are most likely safe to transmit.
I say system because your vehicle, antenna and coaxial cable are all part of this system. When you have a high reading and have to trim you antenna this is really calibrating the antenna to the vehicles body which acts as a ground plane.

May 16, 2010 | Cobra 29 LTD CB Radio

3 Answers

Dont know how to use the swr meter on my radio


With radio turned on

1. Switch the first switch (S/RF SWR CAL) to CAL setting
2. Key mic up &
3. Turn SWR CAL knob while still keying mic until the needle is on the red CAL arrow at the far end of the meter scale. Unkey mic.
4. Switch the first switch back to SWR setting.
5. Key mic up again and record SWR reading and adjust as needed.
6. When done adjusting put switch back in the S/RF setting for normal operation.

Do not flip the switch with the mic keyed up.

Jan 19, 2010 | Cobra 29 LTD CB Radio

1 Answer

I have a cobra 25 ltd and when i key the mic the gauge of the db barley goes up. is something wrong ? also the gauge says its measuring tx power what does that actually mean/ do


TX means transmit. There are 3 settings for the meter. The top one is to measure your TX/RX that's transmit and receive. CAL is to calibrate the meter to check your SWR.

Reasons your needle may not be moving much when you key while on TX/RX. The dynamic is probably all the way down. That is your mic gain. If you turn that up when you talk the needle will swing more. If the radio is stock and not modded, you can turn this all the way up and leave it.

Also there could be something wrong with the mic. If people can hear you then its not the mic.

If people can hear you fine when you transmit, it may just be a bad meter. Not a big problem, you will just need an external meter to make sure you swr is not high.this is important because if it is over 1.5 you run the risk of blowing the final transistor.

Oct 11, 2009 | Cobra 29 LTD 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

3 Answers

Connex 3300hp radio


Hi,

Based on your post/description:

1. how do i set the swr
Normally SWR are calibrated on your operating channel (where you usually stand-by). This is to maximize transmit power and receive sensitivity. To set SWR, switch to channel of your choice, switch SWR control to CAL, key or press PTT, while pressing PTT rotate ADJ knob until max deflection of needle on meter, release mic, switch control to SWR, key/press PTT, needle reading/deflection is SWR for that channel.

I would suspect that your SWR will vary from your current 1.4. This is because you have too big excursion of channels (240 channels).

2.reading a 1.4
This reading is good enough and should do. However as earlier stated, you seem to have 240 channels which would mean that your radio + antenna moves in a wide bandwidth and since the antenna tuning is affected by frequency, your SWR will also be affected by channel.

Best if you can further lower it down.

3. some cb cant get me
This is because the standard CB radio is only 40 channels. The next would be a 80 channel and then 120 channels.

4. is it my radio
Yes, you have a wide coverage radio almost an extended 10 meter rig.

5. do i have to set my radio on high or low to set my swr
I will assume you are referring to power output, set it to HIGH when doing SWR calibration

Hope this be of some help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Nov 08, 2007 | Connex 3300 240-Channels Base CB Radio

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