Alpo Posted April 1, 2019 Share Posted April 1, 2019 I was told, many years ago, when I got my first CB, to make sure that I did not key the mic unless an antenna was hooked up. Doing so would do severe damage to the radio. No one ever told me exactly what happened, though. Does anyone know? Link to comment Share on other sites More sharing options...
Sedalia Dave Posted April 1, 2019 Share Posted April 1, 2019 36 minutes ago, Alpo said: I was told, many years ago, when I got my first CB, to make sure that I did not key the mic unless an antenna was hooked up. Doing so would do severe damage to the radio. No one ever told me exactly what happened, though. Does anyone know? With no antenna connected almost all of the power out is reflected back into the final amplifier. This causes the amplifier to have to dissipate this reflected power as heat. Between the heat generated by the amplifier and the extra heat generated by the reflected power, you exceed the power dissipation capabilities of the amplifier and it naturally fails.. CBs are built very cheaply so there is no circuitry to detect the reflected power and shut down the amplifier preventing damage. More expensive transceivers have extra circuity that detects excessive reflected power and takes steps to prevent damage. Usually the limit is when reflected power is within 10 db of forward power or a 2:1 VSWR. If your CB was transmitting 5 watts of RF power and a VSWR meter was measuring 2:1 then 0.5 watts of power are being returned to the amplifier causing it to have to dissipate 5.5 watts or of energy. This is very close to the design limit and a greater VSWR will likely cause the unit to fail. If the VSWR was 1.5:1 then only 0.2 watts of energy would be reflected back and the circuitry could handle this extra energy. Note This explanation is simplified and my numbers are not exact but it covers what is happening at a high level and the values are close enough for 99% of all applications. Link to comment Share on other sites More sharing options...
The Original Lumpy Gritz Posted April 1, 2019 Share Posted April 1, 2019 What SD sayz is spot on. 73's OLG Link to comment Share on other sites More sharing options...
Pat Riot Posted April 1, 2019 Share Posted April 1, 2019 What SD says and what OLG says is spot on. Link to comment Share on other sites More sharing options...
The Original Lumpy Gritz Posted April 1, 2019 Share Posted April 1, 2019 _ . _ . _ _ . _ OLG Link to comment Share on other sites More sharing options...
Alpo Posted April 1, 2019 Author Share Posted April 1, 2019 Years back, when I was working construction, I had a k40 antenna. This is an expensive antenna, and it easily was taken off the base, so you can store the antenna proper in the trunk. Prevent theft. That's where mine was most of the time, unless I was out roaming around the highway. So I'm crossing the peninsula one time, going from Boca to Fort Myers down Alligator Alley. There's at least a half-a-dozen of us, and though I can hear them talking on my radio, none of them seem to be able to hear me. We carpooled to the job, and I figgered some moron had keyed the mic with the antenna in the trunk, and fried it. Checking my radio when we arrived at our destination, I saw a large dent on one side panel. Could be the result? Took it to a radio shop. Man said he hadn't seen anything like that since Nam. "Son, somebody shot this radio." Migrant construction crew = drunk idiots. Link to comment Share on other sites More sharing options...
Pat Riot Posted April 1, 2019 Share Posted April 1, 2019 1 hour ago, The Original Lumpy Gritz said: _ . _ . _ _ . _ CQ? Link to comment Share on other sites More sharing options...
Alpo Posted April 1, 2019 Author Share Posted April 1, 2019 Nobody's listening. Link to comment Share on other sites More sharing options...
The Original Lumpy Gritz Posted April 1, 2019 Share Posted April 1, 2019 Yup Truth be known-I hate code. I never use it, and barely passed my renewal because of it. OLG Link to comment Share on other sites More sharing options...
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