Re: my uBitx Power

Bill Cromwell

Hi Joe,

You could separate the brown wire that feeds the Drains of the finals and measure just that current. It will probably not be substantially different from the way you did it - subtracting the receive current.

The power you are measuring that way is the DC power *input* to your finals. In the olde dayes the TX power and the vacuum tube ratings were defined in terms of *input* power. That is always going to be higher than the RF output power. The difference will be accounted for by the efficiency. If the finals are 50 percent efficient (a reasonable possibility) and you calculated say 24 watts then your RF output power would be about 12 watts. One details that is good to know is the efficiency of your finals. You will need to measure the actual RF output power and calculate the DC input power as you already have done. Dived theout put power by the input power and get a decimal number less than 1. If that number is 0.5 then your efficiency is 50 percent. It could be less. Probably not much more. Some tube amps made greater than 75 percent! But you could not use them for SSB. If you know the efficency then you can calculate output power by measuring that DC input power and leave your fancy, expensive RF wattmeter in the case at home when you take your radio to Field Day.


Bill KU8H

On 11/01/2018 02:07 PM, Joe Puma wrote:
Hey guys,

I will probably have a watt meter in the coming weeks but I still haven’t measured my power out on the uBitx. So with a dummy load hooked up I took some power measurements with my DMM. I am not sure if this is a good way to tell power output but here are some measurements.

Voltage is 12.67 Radio idle and 12.45 while Tx’ing. not sure which one matters most when calculating power or if the difference is negligible but I calculated wattage from the 12.45v

band current watts
80 2.18 27.14
60 1.50 18.67
40 1.97 24.52
30 1.42 17.67
20 1.65 20.54
17 1.22 15.18
15 1.15 14.31
10 1.0 12.45

If I take into consideration the .33a for radio idle (4w) is my RF wattage 4w less then my measurements.

bark less - wag more

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