CB power measuring
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Post Fiend
Joined: May 2006
Posts: 10,007
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From: Central Florida
CB power measuring
My transceiver pegs the built in power meter, so I've been trying to figure out a way to measure the output. I found this webpage A.H. Systems - RF Related Conversions Basically if ohms law applies, the resistance is 50ohm. So as soon as I get a voltage from my coax, I can square it and divide it by 50 for the power out put. Has anyone tried this or know of another way to do this with a DMM? Any other tricks I should try?
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Post Fiend
Joined: May 2006
Posts: 10,007
Likes: 4
From: Central Florida
My radio is tweaked and tuned, my SWRs are adjusted by a dial on the radio and it shows a perfect 1.5.
I know I am putting out more than 10 watts and the meter I have (internal and external) only does 10 watts of power.
What kind of problem are you having and with what radio? Are your SWRs right? Galaxy says to set to 1.5, anything under 2 is usually fine.
I know I am putting out more than 10 watts and the meter I have (internal and external) only does 10 watts of power.
What kind of problem are you having and with what radio? Are your SWRs right? Galaxy says to set to 1.5, anything under 2 is usually fine.
Fleet Mechanic
Joined: Jan 2007
Posts: 1,741
Likes: 3
You sure you're looking at the right band on the meter? Stock radios swing 16 watts, maybe a tad less. The power band on the meter on my Galaxy 959 goes to 18+ watts.
Most stock meters are little more than modulation meters, and most stock radios will peg internal meters.
Use a POWERED S-meter to check your power ratings; that is, a meter with an external power supply. Non-powered meters will only give you RMS readings. If you don't want to fork over the $$$ for a meter (they're not cheap), then have a shop test the radio. But be careful that the shop is using 12-14 volts on it's bench power supply. Some less-than-reputable shops will run 18 (or more) volts on their bench supply to falsely give higher power readings. The radio's internals may or may not like such high voltage, and the power levels won't be correct.
Most radio signal problems can eventually be traced back to poor grounding on the antenna mount. Even if the mount is mounted to metal, the metal may not have a good ground path back to the frame and/or battery. You may have to run an extra ground wire from the mount to a known-good ground in order to solve your problem(s). (As an aside, I've seen many CB antennas mounted to the plastic mirror arms, and have wondered out loud how poorly those antennas perform.)
Additionally, bed-mounted duals may not give you the best performance if you're running co-phase antennas. The insides of the bed are nowhere near wide enough to give proper antenna spacing, even if your SWR's are reading properly low. Proper co-phase distance on 11-meters (the CB band) is 108 inches, and you can't get that wide anywhere on a SD. You may get better performance by disconnecting your co-ax and running a single line to one or the other antenna, and leaving the other for looks, if you want to run that setup.
-blaine
Most stock meters are little more than modulation meters, and most stock radios will peg internal meters.
Use a POWERED S-meter to check your power ratings; that is, a meter with an external power supply. Non-powered meters will only give you RMS readings. If you don't want to fork over the $$$ for a meter (they're not cheap), then have a shop test the radio. But be careful that the shop is using 12-14 volts on it's bench power supply. Some less-than-reputable shops will run 18 (or more) volts on their bench supply to falsely give higher power readings. The radio's internals may or may not like such high voltage, and the power levels won't be correct.
Most radio signal problems can eventually be traced back to poor grounding on the antenna mount. Even if the mount is mounted to metal, the metal may not have a good ground path back to the frame and/or battery. You may have to run an extra ground wire from the mount to a known-good ground in order to solve your problem(s). (As an aside, I've seen many CB antennas mounted to the plastic mirror arms, and have wondered out loud how poorly those antennas perform.)
Additionally, bed-mounted duals may not give you the best performance if you're running co-phase antennas. The insides of the bed are nowhere near wide enough to give proper antenna spacing, even if your SWR's are reading properly low. Proper co-phase distance on 11-meters (the CB band) is 108 inches, and you can't get that wide anywhere on a SD. You may get better performance by disconnecting your co-ax and running a single line to one or the other antenna, and leaving the other for looks, if you want to run that setup.
-blaine
Fleet Mechanic
Joined: Jul 2008
Posts: 1,937
Likes: 1,221
From: Southern Crescent
Go find a ham radio guy to help you, and have him do this:
Run coax from radio to meter to 50 ohm dummy load, not the antenna. Antennas if not tuned right will screw with your power meter (watt meter)
Your average ham radio guy with HF privileges (General, Advanced or Extra) will likely have all the stuff and do it for free. Or maybe a cold drink.
And a hint about tuning for best SWR. Do it in an open field away from power lines, buildings, fences, etc. Also close the cab doors, bed covers, etc. Have the truck in the same "trim" as you will riding down the road. When you change the shape of the ground plane (the truck) it can impact antenna performace.
Run coax from radio to meter to 50 ohm dummy load, not the antenna. Antennas if not tuned right will screw with your power meter (watt meter)
Your average ham radio guy with HF privileges (General, Advanced or Extra) will likely have all the stuff and do it for free. Or maybe a cold drink.
And a hint about tuning for best SWR. Do it in an open field away from power lines, buildings, fences, etc. Also close the cab doors, bed covers, etc. Have the truck in the same "trim" as you will riding down the road. When you change the shape of the ground plane (the truck) it can impact antenna performace.
Cargo Master
Joined: Aug 2003
Posts: 2,241
Likes: 1
From: Here and there
I think its a grounding issue for my set up since I dropped to a sigle antenna. I just have to work the issue. I see a few grounding straps in my future, but for now it s back to the ol standby my K40 on the roof of the truck. I might even keep it there as the swr is great. I just don't know. Will see what happens when I try and ground the truck some more. I just had my cb tweaked and I can tell you that needle on the cb is kind of like your MPG screen on the truck, it kind of lies. I would honestly get a good external swr meter and test it. You might be surprised what it is.
Senior User
Joined: Feb 2004
Posts: 181
Likes: 0
From: NJ
Also check out this site for more info. It's geared more towards Ham radio, but RF is RF.
Welcome to KØBG's Web Site
Lots of info on mobile installs. Power, grounding, etc...
Bob
Welcome to KØBG's Web Site
Lots of info on mobile installs. Power, grounding, etc...
Bob
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