K5LAD - 50 Years of Ham Radio Memories

Volume XXII

“I wanna git me one of them thar Hopper tubes”

My, but times have changed.  Back in the late 1950s, when I got my first ham license, I was just a green Novice.  If you’d placed all the electronic knowledge I had on one side of a balance scale and placed all I needed to know about radios on the other side, the “don’t know” side would have been so high as to be up in the nose-bleed section.   I’ve already admitted to many of my early areas of “unknowledge” but I was learning much and learning quickly (I hope). 

 Back in those earlier days, few hams owned the equipment to accurately measure the output power of their transmitters.   There were the famous Bird wattmeters available but most were exiled to the laboratories and hamshacks of only the well-to-do hams and I didn’t know any of those guys.  Those Birds were the things that most hams dreamed about owning but doubted that they ever would.

Instead of bragging about the output of your new home-brewed or commercial transmitter or amplifier, you talked about the “input” for that device because it was easily measured.  Power input was defined as the plate voltage (in volts) times the plate current (in amps) of the final stage of the device.   For example, a transmitter running 900 volts at 150 milliamps (on the final amplifier)  would have an input power of 135 watts (900 x .150).  Both the voltage and the current were easily measured by available meters so the input could be easily calculated. If you did have access to a Bird wattmeter, you could place it between the transmitter/amplifier output and the antenna and it would read the power output.   The output was always lower than the input because some of that power would have been used up as heat and/or mismatches in the output stage.  Hams often talked about the plates on their final tube/s glowing cherry red --- heat.  The difference between the input and the output showed the efficiency of the tube and the circuit.

Take, for example, a transmitter that displayed on the meters, a plate voltage of 662 volts and a plate current of 151 milliamps (or .151 amps).  Rounding up a bit gets you 100 watts input.  If the output efficiency was 60%, and you had that Bird wattmeter, you would read approximately 60 watts output.  Input time efficiency is the output.

Back then, the FCC rules reflected this way of power calculation and most hams were allowed 1000 watts input on CW and AM and later allowed 1500 watts PEP (peak envelope power) for SSB (single sideband).  Novice licensees were only allowed, by law, 75 watts input.

There was a local Novice ham who was also near the bottom of the hill in his electronics knowledge.  Ordinarily, I would not identify him by name but since the name is a part of the story, I must let you know that his last name was Hopper.  I’ll provided no more identity clues to him as he might some day see this. We young hams often got together to discuss our ham activities as well as current and proposed projects.  On one occasion, we were having one of our group discussions and the topic turned to power and what was legal for Novices.  This local Novice said something to the effect of, “Well, the FCC says we can only run 75 watts input but they don’t say anything about output.  That means we can run as much output as we want.”  The discussion stopped while the other participants looked at each other. I don’t know how many times, in our later years that, we’ve discussed building a transmitter with some of those ‘Hopper tubes’, an obvious miracle of electronics which allowed the user to run more output than input.  That’s no small feat, either.  Gee, I wonder why the handbooks and textbooks never elaborated on those amazing devices…………. must be some kind of evil plot.

In later years, when devices for measuring power output became more obtainable by the average ham, the FCC changed the rules to show the maximum power usable by a United States ham to be 1500 watts.  There are other countries who permit only lower amounts and a few that allow a full 2KW output.

An entry from Wikipedia on Amateur Radio licenses says:

The amount of output power and amateur radio licensee may legally use varies from country to country. For example, the highest license classes are permitted: 2 kilowatts in most countries of the former Yugoslavia. 1.5 kilowatts in the United States, 1 kilowatt in Belgium and Switzerland, 750 watts in Germany, 500 watts in Italy, 400 watts in India, Singapore, Australia, & United Kingdom, and 150 watts in Oman. Lower license classes are often restricted to lower power limits. For example, the foundation license class in the United Kingdom has a limit of just 10 watts.

Output power may also depend on the mode of transmission. In Australia, for example, although 400w Peak Envelope Power may be used for SSB transmissions, FM and other modes are limited to 120 watts. http://en.wikipedia.org/wiki/Amateur_radio_license

Our nearby neighbors, the Canadians, can run up to 2000 watts.  That benefit must be a trade-off perk given because they also have curling as a major sport.