[Elecraft] WHY HIGH RF OUTPUT??? (c/o AD6XY)
JIM DAVIS
nn6ee at astound.net
Sat Feb 7 14:07:22 EST 2009
On Sat, 7 Feb 2009 02:38:36 -0800 (PST)
AD6XY <m.j.willis at rl.ac.uk> wrote:
>
> It is a common misconception that Bird Thrulines are a always accurate.
>
> They are good when operated into a matched load and when the signal does not
> have a high harmonic content. If there is reflected power you need to make a
> correction. If there are harmonics, even if at a low level, the sensor can
> read much higher power than is actually present, even into a well matched
> load. Bird Slugs can become damaged, mechanically or electrically and I have
> even come across ones with the wrong label.
>
> So, I dispute any claim of accuracy of a power meter just because it is a
> good make. All power meters can on occasion give incorrect readings.
>
> The Bird 43 claims 5% of FSD accuracy. On a 250W slug an error of 12W. 180W
> could, within the meter specification be 170W. Then the 250H slug also has a
> frequency response.
>
> To the problem in hand:
>
> The low pass filtering in the K3 should prevent any over-reading being the
> harmonics, unless there is a problem in the filters and assuming there is
> not a mis-match, we have to assume this power is real.
>
> Specs indicate approx 18A at 13.8V, which is 250W input for 100W output. To
> get 170W or even 180W output is possible, but I think the PA is unlikely to
> be linear or long lived if used in this state. If the K3ALC is not working
> the PA may well develop this much power. I would re-visit the power
> calibration using the K3 utility. If that fails there is probably a fault.
>
> A linear amplifier designed for SSB will normally be capable of much more
> power than it's linear specification. Quite possibly double on the lower
> bands where the efficiency may be higher. While the amplifier can produce
> that power, the device may not survive the extra thermal stress.
>
> Mike
******************************************************************************
Mike OC,
Many, many thanks for a logical/definitive explanation!!!
Appreciated it greatly!
Jim/ee
S/N 2406
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