[Elecraft] Measuring Losses in an ATU

Thu Nov 3 23:16:52 EDT 2016

Ha, ha, Ed... excellent comment! I tend to lean toward empirical measurements so, since there are so many variables in the isolated ATU experiment my approach is to let the system stabilize at some temperature and then open it and allow it to return to ambient. Then I seal it up again and energize a resistor (light bulb or resistor) that had been previously included in the enclosure and reach equilibrium at the same temperature with no RF applied. Simple current X volts to the lap calculation will show exactly how much power is required. That's the power being lost. 

It's tedious and time consuming. 

I have not done that with an ATU but I have testing other so-called "passive" devices. That's why I call passive devices power loss devices, Hi! 

Being lazy, I, too, would have bribed the superintendent. 

73, Ron AC7AC

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Dauer, Edward
Sent: Thursday, November 3, 2016 4:13 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] Measuring Losses in an ATU

I loved Ron’s (AC7AC’s) alternative method for measuring power losses in an ATU (reprinted below.)  But if I remember my high school physics correctly, wouldn’t one have to know the specific heat, and the mass, of every bit of matter in the enclosure that participates in the thermal equilibrium in order to calculate the energy loss from the temperature rise?  That made me wonder if Ron offered it tongue-in-cheek.

That suspicion in turn called to mind the classic story of the bored physics class, in which the students were given a barometer and a battery-powered clock and asked to describe how they would determine the height of a nearby building.  One answer was to drop the barometer from the roof, use the clock to measure how long it took to hit the ground, and then working backwards from the known rate of gravitational acceleration calculate the distance it traveled.  Another was to lower the barometer on a string from the roof just to the point where it missed grazing the ground, start it swinging and then measure the period of the pendulum which is, friction ignored, a constant function of its length.  Third (for the pilots in the crowd), measure the barometric pressure at the roof and at the ground and, using the standard barometric pressure reduction rate and assuming a standard temperature lapse rate, calculate the difference between the two altitudes.  Finally, one fellow who was not destined to become a physicist but rather something else entirely, scoffed at having to climb to the roof.  He said, we’ll just go one flight down to the basement – where we give the superintendent the barometer and the clock as a bribe for him to tell us how tall the building is.

I know it’s OT.  Sorry.  But I haven’t had an excuse to retell that one in years. 

Ted, KN1CBR

On 11/3/16, 3:16 PM, "Elecraft on behalf of elecraft-request at mailman.qth.net" <elecraft-bounces at mailman.qth.net on behalf of elecraft-request at mailman.qth.net> wrote:

    A more direct approach would be to isolate the ATU in a very well insulated
    enclosure, transmit, and measure the temperature rise until it stabilizes.
    You can then calculate how much energy is being dissipated by the ATU and
    becoming heat. That requires the ATU be carefully isolated from the rest of
    the KX3 and be in a very well insulated enclosure to avoid loss of heat to
    the environment, something not practical to do with a KX3. It is, however, a
    valid way to determine losses in external devices like an RF transformer
    (e.g. "balun").

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