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Title: I've lost me mind Post by: Jerry-n5ugw on April 15, 2008, 08:09:20 AM Ok I know I know this, it just has escaped..
I'm trying to determine wether my meter is totally out of whack. I have 1600vdc @150ma into a 50ohm load= ?W My brain is totally toast... Help Title: Re: I've lost me mind Post by: w3jn on April 15, 2008, 08:41:09 AM I presume you aren't dumping 1600VDC into a 50 ohm load, you're talking about the plate voltage and current from a tube final of some sort?
Depends entirely on the efficiency of the amp. 1600*.150 = 240 W from your PS. 50% efficient would be 120W output, for example. Title: Re: I've lost me mind Post by: Jerry-n5ugw on April 15, 2008, 08:45:40 AM Yep I just totally lost all continituity in the ol brain this morning. Thanks.. 1600vdc x.15ma Plate to three 572b's. into 50 ohm dummy load. Gota re cal the meter.
Title: Re: I've lost me mind Post by: k4kyv on April 15, 2008, 12:24:35 PM 1600*.150 = 240 W from your PS. 50% efficient would be 120W output, for example. And pretty typical for amateur transmitters. Rarely does one see that 75% or 80% efficiency as listed in the tube data sheets. The given power output figure is the output at the plate of the tube, and doesn't take into account the losses in the tank circuit, antenna tuner (if used) and feedline. Most amateurs would be disappointed if they were to take an accurate reading of their output power as measured at the feed point to the radiating elements of the antenna. Title: Re: I've lost me mind Post by: KB2WIG on April 15, 2008, 01:25:23 PM “What a terrible thing to have lost one's mind. Or not to have a mind at all. How true that is.” D. Quayle Title: Re: I've lost me mind Post by: Jerry-n5ugw on April 15, 2008, 01:59:33 PM I can find it I just have to think about where I put it longer now.
Title: Re: I've lost me mind Post by: KB2WIG on April 15, 2008, 02:13:58 PM Thats OK. I let my mind wander and it still hasn't come back ............... klc
Title: Re: I've lost me mind Post by: WA5VGO on April 15, 2008, 08:45:33 PM And pretty typical for amateur transmitters. Rarely does one see that 75% or 80% efficiency as listed in the tube data sheets. The given power output figure is the output at the plate of the tube, and doesn't take into account the losses in the tank circuit, antenna tuner (if used) and feedline. Most amateurs would be disappointed if they were to take an accurate reading of their output power as measured at the feed point to the radiating elements of the antenna. Generally speaking, I've got to agree. I've checked a number of commercial amateur transmitters using a Bird wattmeter and a 50 ohm dummy load. The worst offenders are the novice transmitters that double in the final on 10 meters. Their efficiency at that frequency are typically about 30%. The 100 watt class rigs do better with efficiencies in the low 60% on 80 meters dropping to about 50% on 10 meters. Two standouts are the Viking 500 and the KW-1. Both had efficiencies of close to 75% on 80 meters and better than 60% on 10 meters. Darrell Title: Re: I've lost me mind Post by: Opcom on April 16, 2008, 11:19:07 PM It is as interesting to look at overall efficiency as well as plate efficiency because the slight differences in RF PA efficiency are often eclipsed by the overall electrical efficiency of the equipment. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Even the commercial stuff does not fare too well and has wide variations. RCA BTA-250L - 1500V/250mA DC - 375W DC plate input at 250W carrier output - 66.7% - 1825W 120VAC consumed at 100% modulation of the 250W carrier - about 27%? Link 250-UFS (VHF-Low band FM XMTR with 250TH) - 2KV/250mA DC - 500W DC plate input at 250W output - 50% - 1100W 120VAC consumed at 250W output - 22.7% Maybe the Collins and other specific sets are the exception. |