Today in broadcast we generally rate transmitters by AC in to RF out. For AM transmitters that figure is in the low 90 percent range and the current FMs run at about 74% AC in to RF out.
Sent from my iPad > On Aug 17, 2018, at 11:48 AM, Fred Jensen <k6...@foothill.net> wrote: > > Well, only if you've figured out a way to divide by zero. [:-) > > The term "amplifier efficiency" must have changed dramatically since I worked > in broadcast nearly a lifetime ago. Then, it was the ratio [expressed as a > percentage] of the RF power delivered to the 3 1/8" hardline divided by the > DC power supplied to the amplifier plate circuit. Power to the filaments was > generally excluded by manufacturers seeking to have higher efficiency > numbers. One 10 KW FM transmitter I helped build used four 4-1000A's in > parallel and the filament power was 600 watts. Efficiency, including filament > power was just over 70%. > > To measure the efficiency of a KPA1500 [or 500, or KXPA100, or KPA2] one > would measure the key down RF output and divide it by the key down DC input > power. If it was water-cooled, I suppose one should include the input power > to the pump(s), but no one ever did. SS amplifiers like the KPA(1)500 > probably run class AB<mumble> or its equivalent and have substantial DC input > power even at zero RF input. > > RF output power vs RF input power defines the amplifer's transfer function, > not its efficiency. > > 73, > > Fred ["Skip"] K6DGW > Sparks NV DM09dn > Washoe County > > PS: I really don't recommend trying to get four parallel 4-1000A's to work > anything close to "well" at 90.7 MHz. Apparently, it seemed like a good idea > at the time. [:-) > >> On 8/17/2018 6:24 AM, Charlie T wrote: >> Think zero output with zero drive = zero efficiency. >> Apply some drive, read some output and the efficiency goes up from there. >> >> 73, Charlie k3ICH >> > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to w...@w2xj.net ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
