Question about Motorola Talkabout T7400R (2 Pack) (7 Channels) 2-Way Radio

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I want to take the radio apart, but the antenna and turn on/off knob will not come off. How does the antenna and turn on/off knob come off on a T7400, T7450

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Antenna is fixed and attached to the housing. The front and back housings must be first removed to get to it. The volume knob will pull straight up and off the volume potentiometer shaft. This is risky because the small clip which holds the knob in place usually gets stuck on the shaft and then you run the chance of not getting the knob to stay back on the radio.

Best regards.

Posted on Apr 08, 2011

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My recieve on cb radio doesnt work


Are you sure this is the problem.Some people just don't take the time to read the manual that came with the radio.Looking at the radio did you notice if came on or not,turn the volume knob till you here a click and it should come on.Do you hear a loud hissing noise,if not there is a knob that says squelch on it ,turn it all the way to the left. There may also be another knob that says RF GAIN,turn it all the way to the right. Do you hear anything now?Try hooking up your antenna!!!

Jun 11, 2014 | Radio Communications

Tip

How to build a simple AM transmitter.


Take a old radio apart. In my case a portable GE Am/FM type that also runs off 4 "C batteries. Attach output of CD player or SPKR out to Tuner C1 connection on Old Am. Hook other side to Ground or Metal IF canisters. Attach a small 3 foot wire to C2 side of Tuner. Mine does better in the upper band on 1650 Khz. Tune your Am transmitter to match another radio say around 1650KHZ. The Receiver will be at 1650 the Transmitter may be slighly less on the dial at say 1300-1400KHZ. Just because of the IF harmonic is 455KHZ. It my go into 1/2 harmonic or so. It will sound your audio "LOUD" into transmitter 10-30 feet away. Turn down CD player volume until it is clear(not distorted). Its very sensitive in the section of INPUT it doesn't take much to drive the Transmitter. Keep experimenting until these connections are perfected. Once you get it to work, solder it in place. Play all your favorite songs right on your AM receiver. I get an easy 100 feet range with 3 foot Antenna.Have fun. Also On C1 short it across to that screw on C1 side To AM coil wire with the audio wire SPKR out. It seems to be clear,loud and steady. Drive a ground Rod into earth 6 feet attach to metal IF canisters(Grounding) If you get it to work---put it inside a square box and drill holes and add Volume knobs for audio and Gain knobs. Build a RF pass filter at Antenna to better signal by shunting antenna to ground with a coil(40 turns) 100pf capacitor plus a 1k resistor in series with capacitor,where you attach Antenna Screw and Ground screw in back of your box. Antenna can be mounted outside on a 10 foot pole with 75 ohm coax feeding to transmitter. Build your antenna with 8ft. aluminium pole(tape it off with black tape). It should get decent gain.

on May 09, 2011 | Radio Communications

1 Answer

I can only hear the others. When I talk they can't hear and my red anntenna keeps coming on when I push button to talk.


Assuming the antenna is mounted and grounded correctly,when you try to transmit/talk does your meter needle move to the right with your voice,if it doesn't make sure meter knob is set to receive/transmit or mod[modulate] does it move to right now,if not make sure the mic gain knob is turned up or if it is a power mic,is it turned up&have a fresh battery.The antenna light could mean high swr readings which you will have to adjust by tuning the antenna with the radio meter or external meter,you can search swr adjustment on your computer if unfamiliar..some antenna warning lights are factory set too sensitive but most times are telling you there is a problem.If all is set&tuned properly and you still can't get a local signal to respond, your radios transmit finals could be blown,which you'll need a qualified radio tech to determine..Good luck& 73's

Aug 13, 2011 | Cobra 29 LTD CB Radio

1 Answer

Which pots do I use to calibrate swr and rf meters on 29classic to match extral meter?


VR5 tx power meter VR6 antenna warning light
There is not pot for swr cal internally. I guess the cal knob broad range pot or variable resistor. Swr readings after user calibration knob on front of radio, for meter should be close. Obviously not as good as external with larger scale meter. If you can not calibrate meter on face with this knob your radio may have less than 4 watts deadkey.
Just to be on the same page. Understand that SWR is a reading of antenna system condition or tuning of antenna to vehicle mounting location. This is a brief description.

Jul 07, 2011 | Cobra 29 LTD CB Radio

1 Answer

Cb has power but no squelch,can't recieve or transmit


Begin with
  • Volume knob 12 o'clock position
  • Squelch knob full counter clockwise
  • RF gain knob full clockwise
  • Pa/CB switch to CB
  • Mic plugged in
  • Check coax and antenna connections.
  • Make sure your antenna gommet/insulator is installed correctly or it will directed gound. Treat antenna shaft as it is the positive portion of circuit.
If you have another CB check the antenna system with that rig. To verify it is a radio issue. Then dig deeper Microphone, PLL chip, Audio chip etc.

Jan 11, 2011 | Cobra 29 LTD CB Radio

1 Answer

I just need to know how to use it for conversations and what every turn dial means.


you need to hook this up to an antenna. If you are putting it in a car, you need a mobile antenna, if in a house, you need a base antenna. The antenna needs to be tuned for best SWR or you will damage the radio.

Starting from the left of the radio.

Knob 1. Volume/ squelch. The little knob does the volume of what you hear. Big knob squelches out static noise.
knob 2. Dynamike. This is the volume of your voice transmitted. Its how loud people hear you.
Knob 3. RF gain. This is the receive sensitivity. The higher you turn this, the further you can hear. There is almost no reason for you to have this anywhere but full.
knob 4. Delta Tune. This knob should be in the center. If you encounter some one transmitting off frequency, you can move your receive up and down frequency so you can tune that person in. It does not effect your transmit frequency.
Knob 5. CAL. This is to calibrate the meter for taking an SWR reading off the antenna.

Switches starting form the left.

Switch 1. Meter switch. S/RF - will show on the meter, Your signal going out when transmitting, and the signal coming in while receiving. SWR - will show on the meter, your SWR on that channel after you have calibrated the meter. CAL - This is used to calibrate the meter in conjunction with the CAL knob.

Switch 2. ANL - Automatic noise limiter. - This gets rid of electrical interference noise from the vehicle, or other interference sources. ANL/NB - This is the same as ANL, but with NB "noise blanker" This function blanks louder noises that may make it hard to hear people. It's kind of like an automatic squelch, but not nearly as effective as the actual squelch. Also, NB will lessen your receive in that, really low signals will be blanked out.

Switch 3. CB - the radio is in CB mode. This is the normal operation mode of the radio. You can transmit and receive as normal. PA "Public Address" - If you hook a PA speaker to the PA jack in the back, you can mount the speaker on the out side of the vehicle, and talk over it (Its loud). Also, anything you receive over the radio when not holding the mic key, will come over the PA speaker. This is useful when you are not in the vehicle, and need to hear when some one comes on the radio.

Switch 4. BRT and DIM - this is the brightness of the meter light and channel display. BRT stands for bright.

Switch 5. Normal and CH 9, When the switch is in the normal position, everything is normal, but when you flip it up to CH 9 it instantly puts you one channel 9 with out having to turn the dial. CH 9 is the international emergency channel. So it lets you go to Channel 9 quick. when you put it back to normal it will put you on the channel you were on.

Meter explanation. - You have 3 horizontal lines on the meter. the top line is your SWR (only when in SWR mode on the switch. The next one down is you Signal going out. And the bottom one is your signal coming in, in DB's. ***Also noted that part of the SWR line has a CAL )calibration mark. When you have the switch in CAL, and key the mic, you turn the CAL knob up until the needle is at CAL triangle, and then put the radio on SWR and key it. where the needle falls, on the top line is your SWR. If it is in the red your antenna is not tuned, and you can damage your radio.


HERE IS HOW TO TUNE YOUR ANTENN:



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 12, 2010 | Cobra 29 LTD CB Radio

1 Answer

How to set SWR readings to my K40 Antenna without a meter


If you have a cobra 29 then you have a meter. There is no way to Tune an antenna without a meter. You need a device that can read the reflect, or Standing Wave Ratio.That is a standing wave of RF energy that instead of leaving the antenna, is going back down the feed line to the radio and in time hurting the radio.

If you have a cobra 29 LTD, it has a build in SWR meter. It is not as accurate as an in line meter, but it will get it close enough not to hurt the radio. Here is how to do it.

Turn on the radio, with the antenna hooked up. Never key with out an antenna hooked up.

Set the switch all the way to the left(S/RF SWR CAL) to CAL. this stands for calibrate.

You will notice there is a knob right next to the channel selector knob marked SWR CAL as well. Start with the knob turned all the way to the left.

Put the radio on Channel 20. This is just about the middle of the band.

Key the radio and hold it. While holding the key on the mic, turn the SWR CAL knob up until the needle on the meter hits the mark "CAL". there is a triangle, and a gap in the line. The needle needs to be at the point of the triangle in the gap.

NOW, while still holding the mic key, flip the switch from CAL to SWR. You should see the needle immediately swing back. What ever the needle is on at this point is your SWR reading. use the set of numbers on the top of the meter, that's for SWR measurement.

If the needle does not swing back, and is in the rad, the antenna is WAY off. There are some reference points on the scale. The first gap in the line is 1.5 SWR. if the needle is there or less that is fine. then you have 2 and 3. 2 is not so great, but not extremely bad, but you should try to get it lower. 3 is really bad. Anything past 3 is considered infinity, and is really really bad.

If its high, then your antenna is either too long or too short. So how do you know which?

Here is how.

Turn to channel one and repeat the SWR process from above. Make note of the reading.

Then turn it to channel 40. Repeat the process again and take note of the reading.

Now, if the SWR is higher on channel 40 then 1, then your antenna is too long and you must shorten it. If the reading is higher on 1 then 40, then your antenna is too short, and you must lengthen it.

Make adjustments in length about an 1/8th inch at a time until you have either the same reading on 1 and 40 or real close, and or the reading on channel 20 is really low.

If you get it so that the reading on 1 and 40 are the same, then the SWR reading on 20 will most likely be almost nothing, unless there is either something wrong with the antenna, coax, or its just a crappy antenna.

K40 should be able to get a nice low SWR.

Apr 04, 2010 | Cobra 29 LTD CB Radio

2 Answers

Cobra cb brand new and cant get it to work


get your swr checked by a cb shop. 90% of all cb problems are a poorly or not tuned antenna.

Sep 15, 2009 | Cobra 29 LTD CB Radio

3 Answers

Excessive static on AM stations. Waves in and out. Not so on car radio. Is there an antenna to eliminate this?


Turn on the radio and turn the AM/SW BAND switch to the AM position. MW appears in the display. Use the outer ‘fast’ tuning knob to find stations, fine tuning with the inner ‘slow’ knob
when needed.

• If there is interference from adjacent stations, place the BAND WIDTH control in the NARROW position. If there is no interference, leave it in the WIDE position.

• If there is excess background noise, turn on
the SW LPF switch, which may minimize the noise.

• If a station is so strong that audio distortion occurs, reduce the gain level with the AM/SW RF GAIN control knob by turning it counterclockwise.

• The telescopic antenna does not have to be extended for AM reception. The radio has an internal, directional, ferrite-bar antenna for AM reception.

• To optimize AM reception, swivel the radio until maximum signal strength is achieved.

All of that being said: It's very tough nowadays to receive AM in this 2008 electronic world. If your able install a longwire SW antenna outside, and have access to a good earth ground, you can boost the AM signals and beat the noise being generated all around you.

Jan 08, 2008 | Grundig S350 AM/FM/SW Radio

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