"The only thing that shows gross lack of knowledge is not asking the question for which you need the answer." [Cal Poly Physics Professor whose name escapes me but whose class I remember as a personal struggle].
To know the net rate of heat input [i.e. generation within the tuner] from the temperature change, you need to know the mass of the tuner. Weigh it and a little arithmetic and you have the mass. The RF that doesn't heat the tuner must go up the coax. Weighing has nothing to do with the efficiency itself, it is part of the not-exactly-precise-measurement-method I suggested but don't recommend. For the FM transmitter, we had temperature sensors in the grid compartment on the bottom where the refrigerated air entered, and just far enough above the chimneys where it came out hot. There was a water manometer to measure the pressure difference between the air inlet and the vent that took the hot air outside. The pressure differential was very low so I assumed that the air got hot at a constant pressure. This was an important assumption because at that time I didn't know enough calculus for the alternative. I probably don't remember now either. I got up very early one morning [was 17 and living at the TX], and turned on the filaments. When the temperatures had stabilized, and knowing the filaments were turning 600W of electricity into almost 600W of heat, I could calculate the mass rate of the air flowing through the chimneys. Sign on came, I let the temps stabilize at 5.3 KV and 3.5A plate current, and calculated the heat input to give those temps. That power blew out the vent, the rest went up the 3 1/8" rigid coax to the antenna, I assumed. Turned out we were a little overpower, almost 12KW for about 70% efficiency and the 4-1000 plates were fairly bright. OK, really bright. For the case of the tuner, it's not so simple and I skillfully tried to skate past the effect of radiation from the "black body" [i.e. the "black" tuner which, while black, probably isn't a real black body] as the RF heats it. While I know the first six digits of Boltzmann's Constant [138065 -- it used to be the master unlock password for a UHF repeater I maintain], I've forgotten some of the physics and math I used to know and it's guaranteed that, were I to attempt that calculation on this list, a countable infinity of people would correct me and then each other ... likely forever or until Eric stepped in. It was a e-nerd semi-joke, which I've found are not often funny except to other e-nerds. Undaunted however, I continued. Cookie's comment about measuring the efficiency of tuners being hard is very true, and you can't do it with a Micronta SWR meter from Radio Shack. It will involve some math, maybe even calculus, and quite a bit of expensive test equipment. I would trust ARRL's numbers, and those of a few others like Sherwood, I'll remain a little skeptical of the Mfr's numbers, if they even publish them. 73, Fred K6DGW - Northern California Contest Club - CU in the 2012 Cal QSO Party 6-7 Oct 2012 - www.cqp.org On 3/9/2012 3:30 PM, Ian Kahn - Ham wrote: > This probably shows my gross lack of knowledge of the physics involved > here, but what does the weight of the tuner have to do with its efficiency? ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
