Voltage decreases when transmitting

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  • Question
  • Updated 1 month ago
  • Answered
Lately when I transmit the voltage reading on my 6300 decreased. Normally it is at 13.5 and when transmit it goes down to 11.5.

Any suggestion?

73, Santiago
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Santiago Mejia - HI8SMX

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  • concerned

Posted 1 month ago

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Photo of VE3DZP


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Need a heftier power supply if the voltage is dropping and the rig is OK.
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Johan / SE3X

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Hi Santiago, there are fuses inside the cabinet and they need to be cleaned sometimes. Take them out, clean with de-oxit or similar or rubb them with a cloth. 

If you have fuses on the DC cord betwen radio and PS, do the same. Make sure your cabling is as short and as corse as possibel.

I've done this with my 6700 and doing this and thinking about cleaning internal fuses can make wonders for this type of problems.

GL! Johan
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Chris DL5NAM

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.... and before you do this, measure the voltage direct at power supply connectors if you transmit and you will see your psu is to small :-)

The last work what you can do is what Johan says.
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Mike W9OJ

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I took the cover off my 6300 with the intention of cleaning the fuse connections but it appeared I would have to perform major surgery to extract the 30A green fuse. Is there any easy way to get to that thing that I might have missed?

73 de Mike W9OJ
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Steven Linley

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Use a voltmeter to determine where the voltage drop occurs. While TX into a dummy load; Measure voltage at Power supply. Measure voltage as supply line as it enter the radio (inside the radio). Measure voltage on the input side of the fuse, next measure voltage on the output side of the fuse.
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Al / NN4ZZ

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Hi Santiago,

Here are some notes you might find helpful.  


Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
6700 Win10 SSDR V2.4.9

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Al / NN4ZZ

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There are 3 places to measure the voltage to determine where the problem may be.  Power supply issue, cable / connector issue, fuse issue. 

- at the power supply while both RX and TX (suggest 14 - 15 V here)

- at the power pole connector on the back of the radio  ( should be about 0.1 V less than at the supply)

- at the radio side of the fuse with an app like SDRMonitor.  expected drops are in my notes. 

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
6700 Win10 SSDR V2.4.9

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Jean Drolet

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It is normal that at the radio terminals the voltage overwrites but also the amperage.

In the FlexRadio manual it is recommended to have 13.8v +/- 15%. I always adjust to 14.5 volts at the radio terminal
Photo of Dan KG0AQ


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If it is not a power supply issue try cleaning with Deoxit and "slightly" reforming PowerPole connectors per this thread  https://community.flexradio.com/flexradio/topics/undervoltage-powerpole-issue

I had a similar issue and it solved it 100%

73 Dan
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I had this problem. I got my total voltage drop, end to end, down to just .2v
Made a new power cord from a flexible 10ga wire, applied a small amount of a conductive silver grease to the power pole connectors and to the internal power fuses. Voltage is measured with the stacks program. Running my power supply at 14v
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Neal Pollack, N6YFM

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What is "The Stacks Program" and where do we find it?


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Rich McCabe

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It's hard not to get voltage drop with 12 volts DC if you use any significant length of cable. I am a fan of power poles but they contribute as well.

I have a total of about 10' of cable to power the flex which will drop the voltage for sure. So one of my RigRunners is placed under desk at back of radios. I am powering the Flex with a 16" chunk of 10 gauge and the rig runner is powered with TWO 10 gauge runs back to my 50 amp Astron.  I am running 13.5 volts at receive and 12.5 at 100 watts TX.

Best thing you can do is cut the cable as short as possible :)

My voltage is not ideal but when you are dealing with a long run its not easy.