Sandbagger
Administrator/The Boss 
Posts: 6,246 
|
Post by Sandbagger on Nov 4, 2016 7:37:45 GMT -5
During 11/2's roundup an interesting discussion came up. While we joked about it and made light of it, there may be some differences of opinion here. The question is, what constitutes "barefoot" operation? Years ago this was an easy question to answer, as all CB radios available put out between 3 and 5 watts of power, and to get appreciably more than that out, meant that you had to add an external amplifier. So running barefoot meant that you were running the legal limit (more or less) AND you were also running what the radio was putting out on its own, as they were both the same thing. Today though, the waters have become muddied. You now have "export" and the so-called "10 meter" radios that have dual finals, or an additional final stage, which can put out anywhere between 10 and 50 watts carrier. This is certainly well above the FCC mandated limit, but it is still the radio's rated output power.
So where does your opinion fall here? Is "barefoot" still strictly a legal 4 watt radio, or do you feel that it's what a particular radio was designed to put out on its own, without the use of an external amplifier?
|
|
|
|
Post by whitetail on Nov 4, 2016 8:26:44 GMT -5
in a radio operator's eyes, they will call barefoot= what a particular stock radio will put out on its own with NO HELP!
|
|
Sandbagger
Administrator/The Boss
Posts: 6,246
|
Post by Sandbagger on Nov 4, 2016 11:40:33 GMT -5
in a radio operator's eyes, they will call barefoot= what a particular stock radio will put out on its own with NO HELP! I tend to agree with that assessment, but it makes for a bit of confusion on the CB band. There's a wide range of power outputs over the numerous radio offerings out there, and someone running a type accepted 4 watt radio barefoot, will be at a 10 db disadvantage, power wise, compared to someone running a "barefoot" RCI-2990. But technically, it's what the radio is designed to put out on its own. The same situation occurs on the ham bands. Most HF rigs put out 100 watts. Guys will claim to be running "barefoot" when only running the radio's power out. But there are some rigs that put out 200 watts (or more) and some that only put out 25 watts. All of them are considered "barefoot" if they aren't using an external amp. It's even crazier on VHF, with power ranges from 2 watts to 100 watts out of the radio itself. All are considered "barefoot". It makes it easier to think of running "barefoot", strictly as a fixed power level (like 4 watts), because it makes comparisons easier and more fair. While someone could claim that their RCI-2990 is running "barefoot", in actuality, they are running the equivalent of a 4 watt radio and a 2 tube (or transistor) amp. So I can see this side of the debate as well. But like with so many other subjective opinions, your mileage may vary......  |
|
|
|
Post by MonkeyMan on Nov 4, 2016 14:08:54 GMT -5
To me, "barefoot" has always been a radio by itself without the use of an amp. Likewise, "how many watts" you're putting out has always been a separate subject.
|
|
|
|
Post by BBB on Nov 4, 2016 17:10:07 GMT -5
Yes and yes. The definition has indeed changed in the general public with the advent of higher power PA stages within the transceiver casing, possibly due to lack of previous knowledge of the 5 watt CB-50 watt Ham rule. Actually I would lean towards the earlier definition as 5 watt carrier (or less) for CB radio and 50 watts (or less) for Ham radio, but I'm really just showing my age. Barefoot radio New Skool:
(both 400W PEP)   Barefoot radio Old School:  Add one of these into the mix and you're definitely not "running barefoot"   |
|
|
|
Post by cbrown on Nov 9, 2016 14:01:41 GMT -5
To me, "barefoot" has always been a radio by itself without the use of an amp. Likewise, "how many watts" you're putting out has always been a separate subject. I agree. Barefoot is what the radio itself can output with no modifications or external amplifier(s). However, it doesn't mean what it used to. 400 watt out of the box radios didn't exist back then, but they do now. |
|
Sandbagger
Administrator/The Boss
Posts: 6,246
|
Post by Sandbagger on Nov 10, 2016 7:05:27 GMT -5
To me, "barefoot" has always been a radio by itself without the use of an amp. Likewise, "how many watts" you're putting out has always been a separate subject. I agree, but once upon a time, the second follow-up question wasn't necessary because they were the same thing. (barefoot = 4 watts). I'm still waiting for Pete to weigh in here, since he was the one in the strictly "barefoot = 4 watt" camp.  |
|
|
|
Post by 2600 on Nov 23, 2016 17:34:02 GMT -5
Once upon a time, transmitter power was specified by the term "input" power.
Dates back to 1934 and the legislation that created the FCC. Coax cable had not yet been invented. Measuring RF power directly required a lab instrument that cost a year's pay for a working guy with a ham radio.
But Joe ham could afford a DC current meter, to put in line with the power feeding the final amplifier stage of his transmitter. Multiply that current times the voltage that powers the tube, and you get that "input power". And that's what Joe Ham was responsible for measuring, to stay below that 1-kilowatt "input" power limit. Before tubes took the place of spark gaps, you measured the power you pulled from the house current, and the limit for a spark transmitter was 1 kilowatt. When tubes took over, they simply kept that limit in place.
A class-C tube final would deliver at best 70 percent of that to the antenna, around 700 Watts of RF.
CB radio regulations were originally written this way, limiting the final tube's INPUT power to 5 Watts. Would get you around 3.5 Watts of carrier output. Transistors came around some time after that, and they could deliver as much as 80 percent efficiency, for reasons we'll just skip for now.
When the rules were updated in the late 70s/early 80s the legal limits were revised to specify OUTPUT power, measured in the RF feedline coming out of the transmitter. This is the "Four Watt" spec we have become familiar with since the rules were rewritten decades ago.
But if you find a jumper in a 23-channel AM CB radio where the power feeds into the final stage, that's where you insert a current meter into the power feeding the final stage. Legally you were supposed to measure the final tube's current and calculate that "5-Watt input power", multiplying it by the final's power-supply voltage.
As if that's not silly enough, there was a period when SSB was taking over ham radio. There was no AM carrier to limit you to a kilowatt of steady input power to measure. Using the assumption that the ratio of peak-to-average power for SSB was two-to-one, the FCC revised the rule to limit a SSB transmitter to TWO kilowatts of "peak" input power.
In my whole life, I have seen exactly one amplifier that would display the final tube's "peak" current. The "2 kW input" rule was a total fiction, a number that nobody had a way to measure at all. Amplifiers and radios were built with a final-current meter that displayed only the average final current draw.
But "2 kW" sounds a lot better then one kilowatt, and manufacturers use that number to promote their legal-limit amplifiers to this day.
Two just sounds better than one. Even now, that the ham limit has been described as "1.5 kW peak output" for decades.
And where did the FCC come up with "12 Watts PEP" for a SSB CB?
Never have gotten an answer to that one.
73
|
|
Sandbagger
Administrator/The Boss
Posts: 6,246
|
Post by Sandbagger on Nov 24, 2016 9:16:08 GMT -5
Once upon a time, transmitter power was specified by the term "input" power. Dates back to 1934 and the legislation that created the FCC. Coax cable had not yet been invented. Measuring RF power directly required a lab instrument that cost a year's pay for a working guy with a ham radio. But Joe ham could afford a DC current meter, to put in line with the power feeding the final amplifier stage of his transmitter. Multiply that current times the voltage that powers the tube, and you get that "input power". And that's what Joe Ham was responsible for measuring, to stay below that 1-kilowatt "input" power limit. Before tubes took the place of spark gaps, you measured the power you pulled from the house current, and the limit for a spark transmitter was 1 kilowatt. When tubes took over, they simply kept that limit in place. A class-C tube final would deliver at best 70 percent of that to the antenna, around 700 Watts of RF. CB radio regulations were originally written this way, limiting the final tube's INPUT power to 5 Watts. Would get you around 3.5 Watts of carrier output. Transistors came around some time after that, and they could deliver as much as 80 percent efficiency, for reasons we'll just skip for now. When the rules were updated in the late 70s/early 80s the legal limits were revised to specify OUTPUT power, measured in the RF feedline coming out of the transmitter. This is the "Four Watt" spec we have become familiar with since the rules were rewritten decades ago. But if you find a jumper in a 23-channel AM CB radio where the power feeds into the final stage, that's where you insert a current meter into the power feeding the final stage. Legally you were supposed to measure the final tube's current and calculate that "5-Watt input power", multiplying it by the final's power-supply voltage. As if that's not silly enough, there was a period when SSB was taking over ham radio. There was no AM carrier to limit you to a kilowatt of steady input power to measure. Using the assumption that the ratio of peak-to-average power for SSB was two-to-one, the FCC revised the rule to limit a SSB transmitter to TWO kilowatts of "peak" input power. In my whole life, I have seen exactly one amplifier that would display the final tube's "peak" current. The "2 kW input" rule was a total fiction, a number that nobody had a way to measure at all. Amplifiers and radios were built with a final-current meter that displayed only the average final current draw. But "2 kW" sounds a lot better then one kilowatt, and manufacturers use that number to promote their legal-limit amplifiers to this day. Two just sounds better than one. Even now, that the ham limit has been described as "1.5 kW peak output" for decades. And where did the FCC come up with "12 Watts PEP" for a SSB CB? Never have gotten an answer to that one. 73 The thing about measuring input power to calculate output is that it assumes you are totally in resonance when you make your measurement. If not, then you are actually drawing more power than you would otherwise be putting out, and your efficiency will be far less. There was a lot of consternation in the ham radio community over power ratings, when they switched from input to PEP output. The AM guys were aiming for that 1.5 KW max as their carrier power, and after a bit of a back and forth battle, the FCC clarified that the 1.5 KW was to be peak modulation power, which meant 375 watts carrier max (for 100%). They were not happy.... As for the 12 watt CB SSB rating, my theory on that is that if you use a typical peak reading wattmeter, 100% modulation on AM usually shows up as 3 times the carrier power, or for a 4 watt radio, it shows as 12 watts of peak power. But if you read it on a scope, you actually have 16 watts of peak power, as you can display the real 4:1 peak:carrier ratio. I assume that the FCC went with 12 watts for SSB, as it was more common for the average tech to set power by a wattmeter rather than a scope. Of course, I could be completely wrong for assuming the FCC had any method to their madness, and it might have just been an arbitrary value chosen. |
|
|
|
Post by renegade357 on Dec 14, 2016 12:31:43 GMT -5
I agree, what ever the radio puts out is barefoot. Even back when I had purchased my 1988 President Lincoln others stated it was a barefoot radio.
|
|
