I've lost me mind

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Jerry-n5ugw:
I can find it I just have to think about where I put it longer now.

KB2WIG:
Thats OK. I let my mind wander and it still hasn't come back ...............  klc

WA5VGO:
Quote from: k4kyv on April 15, 2008, 12:24:35 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

Opcom:
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.

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.

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