This radio connected to a 25 amp power supply and running high power on Cobra 200gtl.. When transmitting,on high power, the needle moves properly and output power is good for a few seconds then within 2 seconds the power drops off rapidly , needle in meter then does slowly drop away under ssb modulation till it does not react at all. On low power the transmitter is ok ....Any solutions??
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Re: Cobra 200gtl High Power Transmit problem??
Depending on the type of power supply, radio frequency (RF) energy from the transmitter may be 'fooling" it into thinking that you're overloading it. Check to see if there's any discernible dimming of the meter lamp when this problem occurs, if so, the supply is the culprit.
Otherwise, its probable that the final amplifier transistors are overheating, either they are 'leaky' or not properly attached to the heat sink.
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I guess i will have to ask you the most obvious things. Do you have a suitable antenna connected? The needle moves on receive in most cases, not transmit. A watt meter will help you know if you are transmitting.
You have to press the transmit button to get the radio to send a signal that you can calibrate the SWR meter to. If you are pressing the transmit button and nothing is happening then it could be a blown final transistor, a bad switch, bad microphone connection etc.
It sounds like the final transistor may be shorted/burned out. If you don't know how to locate or test the transistor you'll have to take it in to a tech. These transistors are usually quite cheap but as to the labour cost it depends on your tech. Usually what causes this damage is a bad antennae match or a bad antennae itself, even a shorted antennae cable. After you've repaired the radio check the antennae and cable first before connecting it up again, then check your match with an SWR meter. Good luck
Check your antenna. Make sure it is getting a proper ground. If mag mount; make sure base of antenna and where you put it are both super clean. Check where whip goes into coil or base. Make sure all allen screws are tight and whip is not either all the way down to the base or up to the top. If antenna is mounted; make sure that it has a good ground. You might have to remove some paint around the base to get a good connection. DO NOT TRANSMIT WITH A HIGH SWR. YOU CAN BURN OUT THE EXPENSIVE POWER OUTPUT TRANSISTOR. Hope it helps.
hi More than likely your pa transistor has blown have you checked it with a power meter if so r you getting the red tx led when the ptt is pressed if so then your problem lies with the rf transistor
replacing rf transistor
either he over tuned it and burned the radio out this can happen just cause a radio transmits 50 watts dosent mean the circuity can handle it and it will burn the radio because of overload. another factor is if you are running high swrs with that kinda out put you will fry it sounds like its getting hot and radios dont work well when they get hot take it to a tech tell him what was done to the radio and what it is doing. you can test the radio by buying a watt modulation meter it will tell you excacley what the radio is putting out I doubt its transmitting 50 watts that is a single final radio unless he modified the final.good luck.
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.