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Will a short on the antenna of a cover 148 got blow the output transmitter or the power stabilize diode

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Yes, very quickly

Posted on Sep 14, 2014

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SOURCE: low output power

On the meter you are using, does it mesure Average power or peak envelope power?

This is very important to know when you are measuring.

AVG measures basically your dead key. It usually will very little if at all.

PEP measures your peak output, or swing. Modulation.

So even if you have a radio that has been peaked, on a meter that reads AVG, it will still read around 3 to 4 watts. And, if it has a swing kit in it, it will read even less. A swing kit lowers the dead key it increase modulation. Higher PEP.

For example. I peaked my cobra 29 and it does some where around 22 -25 watts PEP. I have variable power in it as well, but usually run the dead key at 2 watts because I have a linear. The Radio alone, when mesureing on PEP with key up at 2 watts, and then when you talk, swings to about 22 -25 watts.

If I flip the meter to AVG, it stays at 2 watts even with talking.

If you have one of those cheap pyramid meters, etc, they usually only read AVG.

Get a meter from radioshack. They have a fairly decent radio for the money. It reads both PEP and AVG and has SWR as well.

If the radio has been peaked and it has a swing mod, it will most likely be swinging to some where in the 20 watt range.

On a side note. According to FCC regulations, a CB radio is only allowed to transmit with 4 watts of final power. Most times the manufacturer will have it a hair under so that they are leagal.

Basically it is illegal to use a CB that puts out more then 4 Watts.

But its a free for all these days. There is no more funding to the FCC for monitoring CB radio, so they do not want anything to do with it. As long as you don't over do it, have over 50000 watts and terrorize a small community with RF, you can do what you want.

Now a days most cb radio's bought have already been peaked if you got it from a cb shop, or off a website that does it.

Posted on May 03, 2009

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1 Answer

Cobra 142 very low rf output


Check your antenna, cable and all connectors. It is common for power to fluctuate if you have any short anywhere in the radio to antenna system. Do not test your radio without an antenna attached or what is called a "dummy load", you may fry your transmitter. Do not trust cheap cables that are pre assembled, I've had many bad out of the box.
John L.

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When i turn it on i get a hum that gets louder then the fuse blows. if i turn on stand by before the fuse blows the hum goes away


Most likely one of the diodes CR6 through CR9 is shorted... Test them with an ohmmeter with the standby switch OFF and no power plugged in either. Slight chance one of the power tubes is shorted but that is rare. A shorted tube socket is another possibility but it too is rare. If one of the diodes is shorted, replace them all as the others are likely degraded. Put a 150 watt lamp in series with the power cord to test to avoid blowing fuses. If the lamp lights and stays on, there i still a short. the filter capacitors may also be degraded if a diode has shorted.

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Power input problem. Keeps blowing fuses, checked cord and it is good, have continuity across positive and return pins of the receptacle...pulled the covers and did not see anything that was obviously...


There should a small diode located near the power input line, "black in color with band on the one end" chances are it is shorted, blowing the fuse. This is a protection diode preventing a positive/negative mix up, if this turns out to be the problem check to make sure the audio is working, if not! you must replace the ic chip.

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Puts out very little


output transistor gone or power turned down on front control,

May 09, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

My cobra 29 is receiving but is not putting out, what could be the problem


The output or transmitter may have been burnt out by any number of factors which include using the radio without a proper working antenna, shorted antenna, lightning/ power surge etc...
Sometimes the mic or wires are damaged.

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Burned magnetron antenna


The average multimeter does not output enough voltage to forward bias a high voltage diode, so it will seem to read open. This is normal.

It still may need a new high-voltage diode and stirrer, and the cavity may be affected.

GE had a campaign (but not a recall, mind you!) covering several models.

Details are in their bulletin at http://207.234.249.73/mwd/ge_mw_mag_kit_bulletin.pdf

The parts kit (that GE used to pay for) is part # WB27X10489 and is shown in the photo below.

If you or a friend decide to look into it, we have critical information on safety, disassembly and door switches at our site, and our link is at our listing here on FixYa: http://tinyurl.com/yzjozk

You can find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383

Chances are GE won't cover any of this, but just in case you want to contact them, GE Customer Service is at http://www.geappliances.com/service_and_support/contact/

We're happy to help and we appreciate your thoughtful rating of our answer.

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Huge static busts


Hi,

Most if not all CB radios have a reverse protection diode soldered immediately right after the power connector. Its purpose is to provide a practical short if the wires are connected wrongly to a power source. This would cause the fuse to blow. The diode normally goes bad after a reversed polarity connection and therefore would need to be replaced. This diode is not in series with the B+ line but connected parallel to the power.

In some instances, other components would also fail: Power capacitors, Audio IC, TX finals and/or the switching/regulator IC.

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

Good luck and kind regards.

Dec 17, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

Signal meter


The signal meter would go into the antenna path something like this:

Oct 06, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Shorts


Could it be in the HV circuit? first you isolate h/output section from power supply. make power supply output ok. check h/output section for short circuit 1 print short near eht 2 diodes or cap.near eht 3 yoke H winding just by removing connector 4 EHT transformer regards

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