[Amps] PA efficiency

[Dr. David Kirkby]

On 05/19/11 02:17 PM, Ron Youvan wrote:
>> On 18 May 2011 13:20, Carey Lockhart, KC5GTT<kc5gtt at gmail.com>   wrote:
>>> I was afraid of that. 58.3%. my gs31 2 meter amplifier i use for a standby
>>> isn't much more efficient than my gs-35 that just croaked. i have been using
>>> these yu1aw designs. have yet to get the rated operating parameters listed. i
>>> don't even have a clue where to start. i am wondering if there is a more
>>> proven design better suited to my skill level. any suggestions?
>
>>> Carey, kc5gtt
>
>> It's totally pointless stating the efficiency to 3 significant figures
>> (58.3%). Whilst if you use a DVM you can read DC voltages and currents
>> to well under 1%, you wont be able to measure the RF power to anything
>> like that accuracy. So your efficiency is probably somewhere between
>> 48% and 68%. So worrying about the odd 1 percent is totally pointless
>> unless you use professional, laboratory quality test equipment to
>> measure the RF power.
>
>> In fact, I doubt your high voltage probe is sufficiently to measure
>> the voltage to better than 1%.
>
>> Dave
>
>     I measure the Voltage with my Tektronix 475B.  That's why I bought it.

I don't know what one of those are, but the biggest problem is measuring RF 
power accurately. Let's be honest, it makes very little practical difference if 
you are running 90 W or 110 W, so a power meter that says 100 W and is accurate 
to +/- 10% is probably ok for most purposes. If however you want to start 
stating efficiency and giving 3 significant figures, it becomes a whole new ball 
game.


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