Dr. David Kirkby wrote:
> Alex Eban wrote:
>
>> Guys:
>> +/- 10% equals 0.4dB error. I don't know of many general purpose instruments
>> that are better than +/- 1dB which is about 20%. Don't go too far. The Air
>> Force and the army use either Birds or Philco-Sierra power meters for
>> testing military and airborne equipment and it's good enough. When you go
>> into single digit percent figures, you're talking about tenths or hundredths
>> of dB less than the thickness of the meter's pointer on an analogue meter.
>> It's meaningless from a practical standpoint. Be reasonable!
>> Alex 4Z5KS
>>
>
> I am being reasonable. In one of my earlier posts I said:
>
> "I can't really think why a ham needs to know RF power very accurately. In
> which
> case, Bird 43's are fine."
The answer for most hams is..They don't need to know how much power they
are running out except for a reference...IOW the rig isn't putting out
as much as it used to.
But for those running power there are two reason I can think of if they
want to stick strictly within the regulations.
When operating the full legal limit to be strictly legal you need to
take into account meter errors. IOW if running 1500 out and the meter is
only 10% you'd want to err on the low side or never run more than 1350
watts indicated.
Also, when doing exposure limit calculations you either need to know the
power into the antenna accurately or err on the high side of
measurement. IOW treat it as if the meter reads high instead of low.
Here, it calculates out that I'd be limited to 360 watts continuous
carrier, but on SSB with a 20% duty cycle plus the on time, I could run
the legal limit. With CW it'd be 900 watts but if I take into account
the "on time" I could still run the legal limit. OTOH with FM or
digital, I'd have to stick with the 360 watts into the antenna as I
sometimes tend to get long winded. You do have to take into account feed
line losses as well.
So in these cases, IF the ham wants to stay legal for exposure limits,
yet run the maximum possible power in the controlled and uncontrolled
areas they need to know the power out of the rig fairly close.
Yes, I know this splitting hairs, but as I run just shy of "tilt" for
power, I want to know how much is there with a degree of accuracy better
than 20%, or even 10% even though the person on the other end would be
unable to detect the difference...theoretically.<:-))
Then there is the most important reason of all... bragging rights <:-))
73
Roger
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