CyberWarrior
Member
How would I go,measuring the amp draw from a cb mobile radio,while transmitting ?
I have the meter,just do not know how to do it.
Thanks
I have the meter,just do not know how to do it.
Thanks
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Measure amp draw for radio
- Thread starter CyberWarrior
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How to measure current and power volt meter DMM
Don't forget to make sure your leads are in the right holes on the meter, and start out with the meter on the 10 amp scale just to be safe (assuming your meter has a dial to set the range).
radiation8
Member
Proceed with Caution.
You might want to look at this https://www.youtube.com/watch?v=9Zt3P9bvn8M Youtube video, skip to 2:25mins for visuals but imagine the CB radio in place of the Drill, but on almost every meter, You have a common (Black) side and 2 Hot (Red) sides, where the meter leads plug into.
One Side is for Volts, Ohms, Continuity, and the other side is for Amps.
To measure Amps, Plug the Red Lead into the Side (or hole) marked for Amps , if it doesn't say Amps, it may be marked "10A, 20A, or Load, or Ampers" Black to Black as normal.
You may want to try this on a 12volt battery with a 12v LED or Normal 12volt Lamp first to be safe.
With the Red Side of the Meter Completely unplugged from the Meter, proceed. As some meters do not have a separate on/off switch I have seen some meters throw volts between the off position and Amp position.
1. Unplug the CB unit, power off and make sure the wires can not touch!!!!!!!!!!
2. Plug Just the ground wire into the radio like normal (wither its from your chassis ground or neg side of the battery)
3. From the Red(12v) wire from the battery attach this to the RED side of the Meter Lead.
4. Attach the Black (Neg, or common) Lead from the meter to the Hot(12v) side of the Radio.
5. Turn your meter to the Amp (Current) position it may be marked with DC10A or ADC, or Just A In bold RED LETTERS.
6. Then plug the Red lead into the Meter Marked appropriately , and this should give power to the radio and instantly start giving you a reading of the Amps, at this point you can turn the radio on, and try to transmit.
Note: depending on what kind of meter you have it may not be very quick and not able to read peak amps, unless it is a true RMS meter or a meter with Peaking function.
As we are dealing with DC, RMS or average should be the same. for an AM or SSB transmitter, power (or current) draw will depend on modulation. I would hook the radio to a dummy load (so as not to interfere with anything). then key the mike and transmit a tone. Start with a low level tone and increase (while watching the meter) the level of the tone till there is no more increase. That should be at 100% modulation or whatever radio limits modulation to. That will also let you know how 'loud' to speak into the microphone-any more will just cause splatter or limiting.
The instructions above are great for how to hook up your meter-remember to set for DC current.
As a 'rule of thumb' most AM gear takes about 2-1/2 to 3 times the 'output' rating so a CB at 4 watts I would expect to go up about 10-12 watts from receive to transmit. Assuming 13.8 volts that would be 10 W/13.8 V or .724 amps. the Receive current depends on volume and many other factors like panel lighting. A 4W CB should not need more than 5 amps. 12 W PEP is actually about the same with a single tone.
Hope this helps
The instructions above are great for how to hook up your meter-remember to set for DC current.
As a 'rule of thumb' most AM gear takes about 2-1/2 to 3 times the 'output' rating so a CB at 4 watts I would expect to go up about 10-12 watts from receive to transmit. Assuming 13.8 volts that would be 10 W/13.8 V or .724 amps. the Receive current depends on volume and many other factors like panel lighting. A 4W CB should not need more than 5 amps. 12 W PEP is actually about the same with a single tone.
Hope this helps
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